Fatima Belhadj

Zahira Kibou

Mohammed Benabdallah

Mohammed Aissaoui

Mohammed Nadjib Rahmoun

Didier Villemin

Mohammed Nadjib Rahmoun

Noureddine Choukchou-Braham

Synthesis and Biological Evaluation of New Chromenes and Chromeno[2,3-d] pyrimidines

est destinée au dépôt

Introduction

The fusion of chromene fragments with different heterocycle scaffolds gives rise to a new class of hybrid heterocycles: 5H-chromeno [2,3-d] pyrimidine. These motifs are wellestablished in the literature as important biologically effective heterocyclic compounds. 1,[START_REF] El-Wahab | Synthesis, reactions and evaluation of the antimicrobial activity of some 4-(p-Halophenyl)-4H-naphthopyran, pyranopyrimidine and pyranotriazolopyrimidine derivatives[END_REF][START_REF] Karimi | Synthesis of new 3H-chromeno[2,3-d] pyrimidine-4,6(5H,7H) diones via the tandem intramolecular Pinner/Dimroth rearrangement[END_REF][START_REF] Haggam | Synthesis of pyrano[2,3-d]pyrimidine-2,4-diones and pyridino[2,3-d]pyrimidine-2,4,6,8-tetraones: Evaluation antitumor activity[END_REF][START_REF] Ghahremanzadeh | Chromeno[2,3-d] pyrimidine-triones synthesis by a three-component coupling reaction[END_REF] These compounds are the subject of many research studies due to their large potential for pharmacological activities. These activities include antitumoral, [START_REF] Eiden | Synthesis of CNS-activity of pyran derivatives: 6, 8-dioxabicyclo (3, 2, 1) octane[END_REF] antibacterial, [START_REF] El-Wahab | AHF Synthesis of some new pyrano[END_REF] anti-fungicidal, analgesic, [START_REF] Meepagala | New class of algicidal compounds and fungicidal activities derived from a chromene amide of Amyris texana[END_REF] anti-allergic, [START_REF] Kitamura | In: European Patent 163599[END_REF] cardiotonic, hepatoprotective, [START_REF] Churchill | Improved synthesis of substituted pyrido[2,3-d]pyrimidinediones[END_REF] antihypertensive, [START_REF] Johannes | Zrcatalyzed kinetic resolution of allylic ethers and Mo-catalysed chromene formation in synthesis. Enantioselective total synthesis of the antihypertensive agent (S, R, R, R)-Nebivolol[END_REF] activity.

In continuation of our efforts toward constructing heterocyclic compounds, [START_REF] Belhadj | Convenient access to new 4-substituted aminopyrido [2, 3-d] pyrimidine derivatives[END_REF][START_REF] Benabdallah | Advances in spirocyclic hybrids: chemistry and Medicinal actions[END_REF][START_REF] Kibou | Easy solventless synthesis of new mono and bis amino-5Hchromeno [3, 4-c] pyridin-5-one derivatives[END_REF][START_REF] Villemin | Solventless convenient synthesis of new cyano-2-aminopyridine derivatives from enaminonitriles[END_REF] the present work reports an efficient process for the synthesis of 5H-chromeno [2,3-d] pyrimidines derivatives. The key step in our strategy is based on the condensation of 2-amino-3-cyano-4H-chromenes with formamidine acetate. The structures of these new compounds were characterised by spectroscopic analysis and evaluated for their antioxidant and antibacterial activities.

Results and Discussion

The synthesis of the new 5H-chromeno[2,3-d] pyrimidine derivatives was obtained through a two-step method, as shown in Scheme 1. The first step was based on the synthesis of 2-amino-3-cyano-4H-chromenes (3a-h). This step was followed by cyclisation and condensation to the 5H-chromeno [2,3-d] pyrimidines in the second step.

Synthesis of 2-amino-3-cyano-4H-chromenes (3a-h)

The general synthesis of 2-amino-3-cyano-4H-chromenes includes the reaction of arylidene malononitriles and β-dicarbonyl compounds in the presence of piperidine, [START_REF] Eszter | Application of ionic liquids in synthetic procedures leading to pharmaceutically active organic compounds[END_REF] triethylamine, [START_REF] Martin | The use of some activated nitriles in heterocyclic syntheses[END_REF] Ca(OH) 2 [START_REF] Raokolla | Ca(OH) 2 -mediated efficient synthesis of 2-amino-5-hydroxy-4H-chromene derivatives with various substituents[END_REF] or TFE. [START_REF] Khaksar | A facile and efficient synthesis of 2-amino-3-cyano-4H-chromenes and tetrahydrobenzo[b] pyrans using 2,2,2-trifluoroethanol as a metal-free and reusable medium[END_REF] Most of these methods involve the use of volatile solvents, expensive reagents and require longer reaction times. We found that these reactions can be carried out without a base and a catalyst. Consequently, 2-amino-3-cyano-4H-chromenes (3a-h) were obtained by condensation of stoichiometric amounts of substituted resorcinol, malononitrile and aromatic aldehydes under microwave for 5 min (Scheme 2).

The results obtained for the preparation of compound 3a-h, with excellent yield (82-97%), are reported in Table 1. The use of microwave allowed us to reduce the reaction time from 24 h to 5 min. NMR spectra of 3a-h showed characteristic signals for 4H-chromenes: singlets at δ H 4.49-4.67 ppm in the 1 HNMR and at δ C 54.87-56.97 ppm in the [START_REF] Benabdallah | Advances in spirocyclic hybrids: chemistry and Medicinal actions[END_REF] CNMR. The IR spectra showed a CN stretch at n 2197-2223 cm -1 , NH 2 stretch at n 3420-3362 cm -1 , CO stretch at n 1670-1675 cm -1 and OH at n 3420-3446 cm -1 . For all the compounds, the mass spectra gave additional evidence for the proposed structures.

The proposed mechanism for the formation of 2-amino-3cyano-4H-chromenes (3a-h) is described in Scheme 3.

Synthesis of 4-amino-5H-chromeno[2,3-d] pyrimidines (4a-h)

Different synthetic methods of 4-amino-5H-chromeno[2,3-d] pyrimidines have been reviewed. [START_REF] Desale | p-Dimethylaminopyridine (DMAP): A highly efficient catalyst for one pot, solvent free synthesis of substituted 2-amino-2-chromenes under microwave irradiation[END_REF][START_REF] Malviya | One-pot three-component synthesis of chromeno [2,3-d] pyrimidine derivatives: Novel, simple, and efficient electrochemical approach[END_REF][START_REF] Mobinikhaledi | Synthesis of some novel chromenopyrimidine derivatives and evaluation of their biological activities[END_REF][START_REF] Ebrahimi | Synthesis of benzo[f]chromeno[2,3-d]pyrimidines via the tandem intramolecular Pinner/Dimroth rearrangement and their antibacterial and antioxidant evaluation[END_REF] In this context and in order to obtain new bioactive heterocyclic compounds, the formamidine acetate was added to the 2-amino-3-cyano-4Hchromenes (3a-h) (Scheme 4) via microwave heating. The originality of our synthetic strategy is based on the use of formamidine acetate as a cyclisation agent. This reagent is a very useful intermediate in synthesising various heterocycles, especially pyrimidine synthesis, through its reaction with unsaturated 2-aminonitriles.

The results obtained for the synthesis of compound 4a-h with good yield (85-95%) are summarised in Table 2.

The treatment of 2-amino-3-cyano-4H-chromenes (3a-h) with formamidine acetate, without solvent and under microwave irradiation for 15 min, gave the corresponding 4-amino-5Hchromeno [2,3-d] pyrimidines (4a-h) with good yields. The IR spectra showed the absence of CN and the appearance of (C=N) at n 1645-1649 cm -1 , NH 2 stretch at n 3465-3402, 3356-3324 cm -1 and CO stretch at n 1671-1675 cm -1 . The structures of the compounds 4a-h were confirmed based on 1 H NMR, [START_REF] Benabdallah | Advances in spirocyclic hybrids: chemistry and Medicinal actions[END_REF] C NMR and MS data.

The mechanism proposed for forming 4-amino-5Hchromeno [2,3-d] pyrimidines (4a-h) was described in Scheme 5. The reaction begins with the formation of the intermediate I.

The latter undergoes a nucleophilic addition of the NH 2 group Scheme 3 Proposed mechanism for the formation of 2-amino-3-cyano-4H-chromenes derivatives (3a-h) The antibacterial activity was evaluated using the broth microdilution method to estimate the Minimal Inhibitory Concentration (MIC) according to the Clinical and Laboratory Standards Institute (CLSI) recommendations (CLSI, 2012). A series of two-fold dilutions from 1024 to 2 µg ml -1 were prepared in a 96 well sterile microplate. These dilutions were inoculated with 100 µl of a solution containing 10 6 colony forming units (CFU).

Gentamicin and Ciprofloxacin were used as positive controls. The microplate was incubated at 37°C for 24 h. The MIC was defined as the low concentration in which there was no turbidity.

Scavenging activity

In our study, the scavenging activity of the compounds was carried out by the technique of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging. The effect of each compound on DPPH was measured by the procedure described by Da Silva Pinto et al. [START_REF] Gupta | An eco-safe approach to benzopyranopyrimidines and 4H-chromenes in ionic liquid at room temperature[END_REF] A volume of 5 µl of various concentrations of each compound was added to 1950 µl of the methanol solution of DPPH. The negative control was prepared by mixing 50 µl of methanol with 1950 µl of the methanol solution of DPPH. The absorbance was measured at 517 nm against a blank of each concentration. These measurements were done after incubation in the dark for 30 min, using a spectrophotometer. The positive control was a solution of the synthetic antioxidant butylated hydroxyanisole (BHA) with concentrations ranging from 0.02 to 0.2 mg ml -1 . The absorbance was measured in the same conditions as the samples. The results were expressed taking into account the average of three measurements obtained for each sample, and the percentage of DPPH reduction was calculated using the formula:

DPPH(%) = (A Control -A Sample ) _____________ A Control ×100
where DPPH (%): Reduction percentage of DPPH.

A Control : Absorbance of the negative control tube. A Sample : Absorbance of the sample.

The IC 50 value is the concentration that was reduced to 50% of the radical DPPH. It was determined graphically for each compound from the curve of the percentage reduction depending on the concentration.

Ferric reducing antioxidant power assay (FRAP)

The reducing power was determined by the measurement of absorbance at 700 nm. [START_REF] Silva Pinto | Bioactive compounds and quantification of total ellagic acid in strawberries (Fragaria × ananassa Duch[END_REF] A volume of 0.1 ml of our compounds in different concentrations (initial) was mixed with 0.25 ml of sodium phosphate buffer (0.2 M; pH = 6.6) and 0.25 ml of potassium ferricyanide 1% (w/v), and the mixture was incubated at 50°C for 20 min. After 0.25 ml of trichloroacetic acid (TCA), 10% (w/v) were added, the mixture was centrifuged at 650 g for 10 min the supernatant (0.5 ml) was mixed with 0.5 ml distilled water and 0.1 ml ferric chloride solution (FeCl 3 ) 0.1% (w/v). [START_REF] Oyaizu | Antioxidative activities of products of browning reaction prepared from glucosamine[END_REF] The IC 50 value (mg compound/ ml) is the effective concentration at which the absorbance was 0.5 for reducing power and was obtained by interpolation from linear regression analysis. For the same conditions, BHA and ascorbic acid were used as a positive control for comparison.

Total antioxidant capacity (TAC)

The total antioxidant capacity of our compounds was evaluated with the phosphor-molybdenum technique. [START_REF] Karagozler | Antioxidant activity and proline content of leaf extracts from Dorystoechas hastata[END_REF] An aliquot of 0.2 ml of different concentrations of our compounds was combined with 2 ml of reagent solution (0.6 M sulfuric acid, 28 mM sodium phosphate and 4 mM ammonium molybdate). The tubes were incubated in a thermal block at 95°C for 90 min. The absorbance of each solution was measured at 695 nm against a blank. The antioxidant capacity was expressed in milligram equivalent of ascorbic acid per gram of compound (mg EAA g -1 C). The range of the calibration curve of the ascorbic acid was 0.10 to 0.80 mg ml -1 (Table 3).

The MIC results of the synthesis products against references bacteria are shown in Table 4.

The higher activity against gram-negative bacteria was obtained toward Pseudomonas aeruginosa. The product 4e showed a MIC equal to 16 µg ml -1 . The products 3e, 3b and 3c showed MICs equal to 64 µg ml -1 . Compound 3d showed a MIC equal to 256 µg ml -1 . However, other gram-negative bacteria exhibited resistance to products tested. For grampositive bacteria, low MICs were obtained by the products 3b and 3c and 4e against the Bacillus cereus strain; the MICs range was 32 to 128 µg ml -1 . The compound 3e showed a MIC equal to 128 µg ml -1 against Bacillus cereus and Staphylococcus aureus.

The products 3b and 3c have Cl or Br halogen groups respectively at the 4-position, while the 3e has two Cl located in the 2-and 4-positions on the aromatic (phenyl) ring. The products with the electron-withdrawing groups in position 4 showed antibacterial activity with respect to gram-positive and -negative bacteria. These results are in accordance with the work of Nirav et al., [START_REF] Barek | Phenolic contents, antioxidant, and antibacterial activities of the Algerian Genista saharae solvent extracts[END_REF] which focused on the synthesis and evaluation of the antimicrobial activity of a new series of 4H-chromenes against Staphylococcus aureus (S. aureus), and Bacillus subtilis (B. subtilis). The best result has been observed with chromene, which has a chlorine group. In the study of Sudhan and Mansoor, [START_REF] Shah | Synthesis of 2-amino-4H-chromene derivatives under microwave irradiation and their antimicrobial activity[END_REF] the synthesis and evaluation of the antimicrobial activity of a new series of 7,8-dihydro-2-(2-oxo-2H-chromen-3yl)-5-aryl-cyclopenta[b]pyranopyrimidine-4,6-5H-dione were investigated; the results suggest that aromatic substituents strongly influence antibacterial and antifungal activities.

In the chromeno[2,3-d] pyrimidines, the products 4e, 4c, 4d and 4b showed interesting activities against Bacillus cereus (B. cereus) and Pseudomonas aeruginosa (P. aeruginosa). The best results were obtained with compound 4e, where the structure of the chromeno pyrimidine is composed of two fused heterocyclic units, namely, the substituted 4H-chromene and the pyrimidine. The pyrimidine has an amine in the 4-position of the ring. Chlorine is well known to have good bacterial activities, as shown in the case of 4e.

These results agree with the work of Agrod, [START_REF] Sudhan | Facile synthesis and antimicrobial activity of a novel series of 7,8-dihydro-2-(2-oxo-2H-chromen-3-yl)-5-aryl-cyclopenta[b]pyrano-pyrimidine-4,6-5H-dione derivatives catalysed by reusable silica-bonded N-propyl diethylenetriamine sulfamic acid[END_REF] who found that the chlorine group linked to chromenopyrimidine heterocycles has good antibacterial activities compared to their analogues. The modification of the 4H-chromene structure through the chromenopyrimidine products allowed the improvement of the antibacterial activity.

In the study of Sankappa et al., [START_REF] El-Agrody | Synthesis and antimicrobial activities of 2-substituted 12H-chromeno[3,2-e][1,2,4]triazolo[1,5-c] pyrimidines, 3-ethoxycarbonyl-12H-chromeno[3,2-e][1,2,4] triazolo [1,5-c] pyrimidine-2-one and ethyl 2-formylamino-and 2-acetylamino-4Hchromene-3-carboxylates[END_REF] the new series of synthesised chromeno[2,3-d] pyrimidine compounds did not exhibit activity against: Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa.

In the antioxidant study, two products (3e and 3d) of the 4H-chromenes family showed good DPPH scavenging activity. The products 3b and 3c have Cl or Br respectively at the 4-position, while the 3e has two Cl located in the 2-and 4-positions of the aromatic (phenyl) ring. The grafting of electron-withdrawing halide substituents in position 4 improve the DPPH trapping activity. In iron reduction and antioxidant capacity, the situation is reversed; products 3b and 3c showed the most interesting reduction.

Concerning chromenopyrimidines, the 4c product showed the most interesting DPPH and iron reduction trapping activity. The grafting of electron-withdrawing halide substituents on the phenyl nucleus seems to improve this activity. The most important antioxidant capacity was obtained with 4e. It seems that the grafting of the electron-donating groups improves this activity.

Finally, we can say that the importance of this research work lies in the possibility that an in-depth investigation of the structure-activity relationship, toxicity and biological effects of these compounds may be useful for designing more potent oxidising agents at higher concentrations for therapeutic purposes.

Experimental

The melting points were measured using a Bank Kofler HEIZBANK apparatus standard WME 50-260°C and were uncorrected. IR spectra were obtained with solids with a Fourier transform Perkin Elmer Spectrum One with ATR accessory. Only significant absorptions are listed in the results. The 1 H NMR spectra were recorded at 400 MHz on a Brüker AC 400 Table 4. MIC values of the synthetic compounds spectrometer, and [START_REF] Benabdallah | Advances in spirocyclic hybrids: chemistry and Medicinal actions[END_REF] C NMR spectra were recorded on the same spectrometers at 100.6 MHz. Samples were dissolved in DMSO-d 6 , values for δ are in parts per million relative to tetramethyl silane (TMS) as an internal standard. Mass spectra were recorded on a QTOF Micro (Waters). Microwave irradiation experiments use a microwave reactor (Biotage). The multiplicities are reported as s (singlet), d (doublet), t (triplet), q (quartet) and m (multiplet).

Synthesis

General procedure 1 for the synthesis of 2-amino-3-cyano-4H-chromenes (3a-h)

A mixture of the aromatic aldehyde (2a-e) (10 mmol), substituted resorcinol (1a-b) (10 mmol), malononitrile (10 mmol), H 2 O (2 ml) and carbonate of ammonium (0.5 g) was irradiated in a single-mode microwave at 300 W for 5 min under 12 bar pressure. The completion of the reaction was determined by thin-layer chromatography (TLC). After the completion of the reaction, the residue that formed was diluted with 30 ml of CH 2 Cl 2 . The organic layer obtained was washed with water (3 × 20 ml), then with a solution of saturated NaCl (10 ml), dried over MgSO 4 , filtered and evaporated under vacuum. The compounds 3a-h were obtained as white solids.

General procedure 2 for the synthesis of-amino-5H-chromeno[2,3-d] pyrimidines (4a-h)

A mixture of 3a-h (5 mmol) and formamidine acetate (15 mmol, 1,56 g) was irradiated in a single-mode microwave at 300 W for 15 min and under 12 bar pressure. TLC determined the completion of the reaction. After the completion of the reaction, the residue that formed was diluted with 30 ml of CH 2 Cl 2 . The organic layer obtained was washed with water (3 × 20 ml), then with a solution of saturated NaCl (10 ml), dried over MgSO 4 , filtered and evaporated under vacuum to afford desired compounds 4a-h.

2-amino-4-(bromophenyl)-3-cyano-7-hydroxy-4H-chromene

(3c) was obtained, according to procedure 1 using 4-bromobenzaldéhyde (10 mmol; 1.83 g), resorcinol (10 mmol; 1.10 g) and malononitrile (10 mmol; 0.66 g), as white solid; 89% a , 93% b , or 97% c ; mp 251°C.

Conclusions

In conclusion, we have successfully developed a novel and efficient approach for synthesising new chromenes and 5H-chromeno [2,3-d] pyrimidines derivatives under solventfree conditions and microwave irradiations with high yields. The originality of our synthetic strategy is based on the use of formamidine acetate as cyclisation agents. This easy to execute methodology with rapid access and good yields open a new route for synthesising various substituted nitrogen heterocycles of biological and pharmaceutical. Evaluating the antioxidant and antibacterial activity of the various compounds tested against three bacterial strains showed good activity.

  First, we have the formation of alkene I by the Knoevenagel condensation of aromatic aldehyde and malononitrile. A 1,4-Michael addition of II with alkene I form intermediate III. This intermediate is converted to intermediate IV by intramolecular cyclisation. A rearrangement of intermediate IV produces the expected 2-amino-4H-chromenes.

Scheme 4 Scheme 5

 45 Scheme 4 Synthesis of 4-amino-5H-chromeno[2,3-d] pyrimidines (4a-h)

  Inhibitory Concentration (µg ml -1 )

Table 1

 1 Results of synthesis of 2-amino-3-cyano-4H-chromenes (3a-h)

	R R1	Products	Yield (%)	Mp Found	°C Reported
		C 6 H 5		95	235	234-237 20
		4-ClC 6 H 4		97	162	161-162 21
	H	4-BrC 6 H 4		97	224	224-226 21
		4-MeC 6 H 4		96	184	183-186 20

Table 2

 2 Results of synthesis of 4-amino-5H-chromeno[2,3-d] pyrimidines (

4a-h)

	R R1	Products	Yield (%)	Mp	°C
		C 6 H 5		90	197
		4-ClC 6 H 4		93	202
	H	4-BrC 6 H 4		91	240
		4-MeC 6 H 4		90	210
		2,4-diClC 6 H 3		95	250
		C 6 H 5		85	206
	Me	4-ClC 6 H 4		89	232
		4-BrC 6 H 4		91

Table 3

 3 Results of the antioxidant activity of the synthetic compound

	Compounds	P. aeruginosa	E. coli	S. typhimurium K. pneumoniae	C. freundii	S. aureus	E. flaecalis	B. cereus

1 H NMR (DMSO) δppm :

  : 9.80 (1H, s, OH); 7.58 (1H, d, J H-H = 2.10 Hz, H arom ); 7.40 (1H, dd, J H-H = 2.10 Hz, J H-H = 2 Hz, H arom ); 7.21 (1H, d, J H-H = 12 Hz, H arom ); 6.98 (2H, s, NH 2 ); 6.72 (1H, d, J H-H = 8.40 Hz, H arom ); 6.49 (1H, dd, J H-H = 2.40 Hz, J H-H = 2.40 Hz H arom ); 6.42 (1H, d, J H-H = 2.00 Hz, H arom ); 5.13 (1H, s, H pyran ).

	(10 mmol; 1.10 g) and malononitrile (10 mmol; 0.66 g), as
	white solid; 88% A , 90% B , 95% C ; mp 256°C.
	13 C NMR (DMSO) δppm : 160.95 (C-OH); 157.95 (C-O-CNH 2 ); 149.49
	(C-NH 2 ); 142.37-120.63(9 × C arom ); 113.5(CN); 112.33 (C=C-O);
	102.74 (C=C-CN); 54.87 (CH-Ph).
	IR (neat cm -1 ): 3417; 3342; 2198; 1647; 1595.
	Results: C 16 H 10 Cl 2 N 2 O 2 M+H 333.1760. Found 333.1762.
	4-amino-5-(4-bromophenyl)-8-hydroxy-5H-chromeno[2,3-d]
	pyrimidine (4c) was obtained, according to general procedure
	2 using 3c (5 mmol, 1.71 g), as white solid; 91%; mp 240°C.
	1 H NMR (DMSO) δppm : 9.98 (1H, s, OH); 9.80 (1H, s, H pyrimidine );
	7.49 (2H, d, J H-H = 8.40 Hz, H arom ); 7.13 (2H, d, J H-H = 8.40 Hz,
	H arom ); 6.91 (2H, s, NH 2 ); 6.78 (1H, d, J H-H = 8.40 Hz, H arom );
	6.54 (1H, dd, J H-H = 2.40 Hz, J H-H = 2.40 Hz H arom ); 6.42 (1H, d,
	J H-H =2.40 Hz, H arom ); 4.64 (1H, s, H pyrane ).
	13 C NMR (DMSO) δppm : 162.84 (C-O); 160.72 (C-NH 2 ); 157.66 (C-
	OH); 149,26 (-N-C=N-); 146,18 (C=C-N); 132.77-120.22 (9 ×
	C arom ); 113.57 (C=C-Ph); 112.96 (C=C-N); 102.72 (CH-Ph).
	IR (neat cm -1 ): 3439; 3440; 1669; 1569.
	Results: C 17 H 12 BrN 3 O 2 M+H 370.0191. Found 370.0203.
	4-
	9.80 (1H, s, OH); 7.49 (2H, d, J H-H =
	8.40 Hz, H arom ); 7.13 (2H, d, J H-H = 8.40 Hz, H arom ); 6.91 (2H, s,
	NH 2 ); 6.78 (1H, d, J H-H = 8.40 Hz, H arom ); 6.49 (1H, dd, J H-H =
	2.40 Hz, J H-H = 2.40 Hz H arom ); 6.41 (1H, d, J H-H = 2 Hz, H arom );
	4.64 (1H, s, H pyran ).
	13 C NMR (DMSO) δppm : 160.72 (C-OH); 157.60 (C-O-CNH 2 );
	149.26 (C-NH 2 ) ; 146.18-120.22 (9 × C arom ); 113.57 (CN); 112.96
	(C=C-O); 102.72 ( C=C-CN); 56.52 (CH-Ph).
	IR (neat cm -1 ): 3457; 3340; 2220; 1645; 1597.
	Results: C 16 H 11 BrN 2 O 2 M+H 343.1703. Found 343.1704.
	2-amino-3-cyano-7-hydroxy-4-p-tolyl-4H-chromène (3d) was
	obtained according to general procedure 1, using
	4-methylbenzaldehyde (10 mmol; 1.20 g), resorcinol (10 mmol;
	1.10 g) and malononitrile (10 mmol; 0.66 g), as white solid;
	85% a , 90% b or 96% c ; mp 184°C.
	1 H NMR (DMSO) δppm : 8.39 (1H, s, OH); 7.11 (2H, d, J H-H =
	8.40 Hz, H arom ); 7.07 (2H, d, J H-H = 8.40 Hz, H arom ); 6.81 (2H,
	s, NH 2 ); 6.78 (1H, d, J H-H = 8.40 Hz, H arom ); 6.52 (1H, d, J H-H =
	8.40 Hz, H arom ); 6.47 (1H, dd, J H-H = 2.40 Hz, J H-H = 2.40 Hz
	H arom ); 4.49 (1H, s, H pyran ); 2.26 (3H, s, CH 3 ).
	13 C NMR (DMSO) δppm : 160.20 (C-OH); 157.53 (C-O-CNH 2 );
	149.88 (C-NH 2 ); 143.36-120.96 (9 ×C arom ); 113.87 (CN); 112.81
	(C=C-O); 103.00 ( C=C-CN); 56.94 (CH-Ph); 21.06 (CH 3 ).
	IR (neat cm -1 ): 3420; 3416; 2217; 1649; 1622.
	Results: C 17 H 14 N 2 O 2 M+H 278.3099. Found 278.3101.
	2-amino-4-(2,4-dichlorophenyl)-3-cyano-6-hydroxy-4H-
	chromene (3e) was obtained, according to general procedure 1
	using 2,4-dichlorobenzaldehyde (10 mmol; 1.75 g), resorcinol

1 H NMR (DMSO) δppm

amino-8-hydroxy-5-p-tolyl-5H-chromeno[2,3-d] pyrimidine (4d

	13 C NMR (DMSO) δppm : 163.08 (C-O); 162.81(C-NH 2 ); 157.57
	(C-OH); 156.86 (-N-C=N-); 150.40 (C=C-N); 142.54-113.13(9
	× C arom ); 112.73 (C=C-O); 103.40 (C=C-N); 96.66 (CH-Ph);
	20.99 (CH 3 ).
	IR (

) was obtained, according to general procedure 2 using 3d (5 mmol, 1.39), as white solid; 91%; mp 210°C. 1 H NMR (DMSO) δppm : 9.68 ( 1H, s, OH); 8.08 ( 1H, s, H pyrimidine ); 7.14 (2H, d, J H-H = 8.00 Hz, H arom ); 7.04 (2H, d, J H-H = 8.00 Hz, H arom ); 6.95 (1H, d, J H-H = 8.40 Hz, H arom ); 6,72 (2H, s, NH 2 ); 6.53 (1H, dd, J H-H = 2.40 Hz, J H-H = 2.40 Hz H arom ); 6.50 (1H, d, J H-H =2.40 Hz, H arom ); 5.09 (1H, s, H pyran ); 3.19 (3H, s, CH 3 ).

neat cm -1 ): 3444

  ; 3413; 1647; 1595. Results: C 18 H 15 N 3 O 2 M+H 305. 3334. Found 305.333 4

-a m i n o -5 -( 2 , 4 -d i c h l o r o p h é n y l ) -8 -h y d r o x y -5 H - chromeno[2,3-d] pyrimidine (4e) was

  obtained, according to general procedure 2 using 3e (5 mmol, 1.66 g), as white solid; 95%; mp 250°C.

1 H

NMR (DMSO) δppm :

  9.78 ( 1H, s, OH); 8.12( 1H, s, H pyrimidine ); 7,52 (2H, d, J H-H = 8 Hz, H arom ); 7.39 (1H, d, J H-H = 8 Hz, H arom ); 6.89 (1H, d, J H-H = 8 Hz, H arom ); 6.53 (1H, dd, J H-H = 2.40 Hz, J H-H = 2.40 Hz H arom ); 6.48 (1H, d, J H-H =2.40 Hz, H arom ); 6.33 (2H, s, NH 2 ); 5.51 (1H, s, H pyran ). 13 C NMR (DMSO) δppm : 163.11(C-O); 163.02 (C-NH 2 ); 158.08 (C-OH); 157.30 (-N-C=N-); 150.50( C=C-N); 140.41-112.84(9 × C arom ); 112.84 (C=C-O); 103.27 (C=C-N); 94.60 (CH-Ph). IR (neat cm -1 ): 3379; 3427; 1647; 1585. Results: C 17 H 11 Cl 2 N 3 O 2 M+H 360.0307 Found 360.0309

Acknowledgements

The authors wish to thank Karine Jarsalé for the mass spectroscopy spectra. We gratefully acknowledge financial support from the 'Ministère de la Recherche et des Nouvelles Technologies', CNRS (Centre National de la Recherche Scientifique), the 'Region Basse-Normandie' and the European Union (FEDER funding). The authors acknowledge the financial support of the French Agence Nationale de la Recherche (ANR) through the program 'Investissements d'Avenir' (ANR-10-LABX-09-01) LabEx EMC. We thank DGRSDST and the University of Tlemcen-Algeria for funding this work.


Florian S U Fischer

Navaphun Kayunkid

Daniel Trefz

Sabine Ludwigs

Martin Brinkmann

Structural models of poly(cyclopentadithiophene-altbenzothiadiazole) with branched side chains: impact of a single fluorine atom on the crystal structure and polymorphism of a conjugated polymer

Abstract

This study describes the impact of a single fluorine atom substitution in the conjugated backbone of poly(cyclopentadithiophene-alt-benzothiadiazole) on the structure and the polymorphism of the polymer bearing 2-ethylhexyl side chains. Controlled growth of the non fluorinated and fluorinated polymers by solvent vapor annealing (SVA), meltcrystallization on oriented poly(tetrafluoroethylene) and high temperature rubbing yield highly crystalline and/or oriented films of a thermodynamically stable polymorph called form I. The single-crystal hk0 and the oriented fiber patterns are obtained in films prepared by SVA and aligned films, respectively. Form I involves a high symmetry packing of four chains in an orthorhombic cell (P c c n space group) with pseudohexagonal symmetry. The chains are paired into dimers with a 3.6-3.8 Å inter-chain stacking distance and a segregated mode of stacking of cyclopentadithiophene and benzothiadiazole (BT). A single H/F substitution on the BT unit modifies the orientation of the dimers in the unit cell of form I. Absorption and structural properties of this new polymorph are discussed with respect to the classical -stacking structure obtained from solvent-additive processed films. Evidence of yet another polymorph (form II) highlights the polymorphism of these alternated donor-acceptor copolymers.

I. Introduction.

Alternating copolymers made of donor and acceptor units in the backbone have attracted much interest due to the possibility to tune their electronic properties by the adequate combination of donor and acceptor units. [1][2][3][4] This strategy has been particularily fruitful to control opto-electronic properties e.g. the band gap of the active layers in organic photovoltaic cells. From a structural standpoint, the alternation of donor and acceptor units implies different possibilities of -stacking between them, the extreme cases corresponding to segregated and to fully mixed stacking. 5,6 As recently reported for Poly[N,N'-bis(2octyldodecyl)-1,4,5,8-naphthalene-dicarboximide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene) (P(NDI2OD-T2)) and earlier for Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole), two different polymorphs corresponding to these two stacking modes were identified and the consequences in terms of optical and device properties were uncovered. [5][6][7] However, to establish structure-property correlations in such complex macromolecular systems, it is necessary to generate high order and crystallinity, which is challenging. A major breakthrough has been achieved by using solvent vapor annealing that leads to highly crystalline films as illustrated recently for -conjugated polymers such as regioregular poly(3hexylthiophene) (P3HT) and Poly [2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT). 8,9 Other approaches to induce high crystallinity and orientation were proposed such as zone casting 10 , epitaxy 11 or hightemperature rubbing. 12 Most semiconducting polymers made of a conjugated backbone bearing alkyl side chains have a "layered" structure made of an alternation of -stacked backbones and layers of more or less ordered side chains. 13 This is the case for major polymers such as regioregular poly(3alkylthiophene)s and poly(2,5-bis(3-dodecyl-2-yl)-thieno [3,2-b]thiophene) (PBTTT). 13,14 However, this type of "smectic-like" ordering is not the only one observed. In the case of the alpha form of poly(9,9'-dioctylfluorene) (PF8) and the gamma form of poly(9,9'diheptylfluorene) (PF7), the chains are grouped into dimers that ultimately form an ordered orthorhombic structure with high symmetry (P n b 21 for PF8). 15,16 In these systems, and contrary to P3HT or PBTTT, no long-range -stacking of the chains is observed.

Regarding the structure of PCPDTBT, several studies by Grazing Incidence X-ray Diffraction (GIXD) on marginally crystalline films obtained by spin-coating suggest that PCPDTBT should also present a layered structure similar to P3HT. In particular the presence of additives such as 1,8-diiodooctane (DIO) in the processing solvent induces these layered structures. [17][18][19][20][21] Such structures were hypothesized from the presence of an in-plane reflection at 3.8 Å and an out-of-plane reflection in the range 10.5 Å -12.0 Å. Recent work showed that highly crystalline PCPDTBT films can be prepared by solvent vapor annealing (SVA) in chlorobenzene (CB). The structure of these PCPDTBT crystals was analyzed by electron diffraction (ED) and a tentative model was proposed for the polymer without taking into account the side chains and using only the hk0 single-crystal pattern. 22 The extinction rules in this ED pattern were compatible with a P n 2 n space group and four chains per unit cell. To our surprise, a packing mode similar to that of -PF8 and -PF7 could be evidenced with pairs of PCPDTBT chains packed in an orthorhombic unit cell. However, in the absence of ED patterns giving information along the chain direction, no precise packing scheme of the chains in the dimer could be proposed. In particular the type of stacking between cyclopentadithiophene and benzothiadiazole could not be clarified.

With respect to optical properties, it was found that the layered structures formed in the presence of DIO exhibit a strong absorption band around 800 nm, which is attributed to stacking. [17][18][19][20][21] The highly crystalline SVA films on the other hand exhibit a blue-shifted absorption and no absorption around 800 nm. 22 (in F-PCPDTBT, one hydrogen atom on the BT unit is replaced by fluorine regio-randomly, see scheme 1). From the point of view of device performance, the introduction of fluorine in the backbone of PCPDTBT results in improved efficiencies in OPV cells. 23 To address the structure of these polymers, highly crystalline samples were prepared by SVA, leading to terrace-like domains with essentially standing chains and typical [0 0 1] ED patterns.

Additional ED patterns were obtained from oriented films of these polymers prepared either by high-T rubbing or by epitaxy on oriented poly(tetrafluoroethylene) (PTFE) substrates.

Absorption spectroscopy of the oriented films revealed a blue-shifted absorption without the 800 nm band, similar to the SVA samples. Two polymorphs are evidenced for both polymers and structural models of the form I are proposed. Chlorobenzene (CB) solvent vapor annealing was employed to obtain highly crystalline samples of PCPDTBT and F-PCPDTBT. The detailed CB-annealing procedures for PCPDTBT have been described elsewhere. 22 For the annealing procedure pre-cast films (CHCl 3 , 3 mg/ml, spin coated) on glass substrates were used. The CB vapor atmosphere and the substrates were heated to 50°C and 40-42°C, respectively and the films swollen to a solution-like state at a vapor pressure of 80-90%. Recrystallization was subsequently induced by slowly decreasing the vapor pressure down to 73 -70%.

The CB-annealing method was slightly modified for F-PCPDTBT due to its stronger aggregation behavior which prevented a swelling of the pre-cast films. The substrates were covered inside the solvent vapor chamber with a CB solution (0.1 mg/ml) and equilibrated for 10 min by purging the chamber with a CB vapor of 92% and holding the substrate and vapor at 42°C and 50°C, respectively. During this time a thin homogenous film of the solution was formed which was afterwards recrystallized by reducing the vapor pressure to 74%. Within 900 min the film was recrystallized completely and could be quenched by pure nitrogen.

c) Melt-crystallization on friction transferred PTFE substrates

Oriented PTFE substrates were prepared by friction transfer on clean glass slides using the protocol described in the literature. 24 Thin polymer films (3 mg/ml, CB) were cast on oriented PTFE substrates and melt-recrystallized in a Linkam hot stage (THMS 600) under argon atmosphere (melting at around 290°, cooling at 0.25 K/min to 280°C for 4 hrs, final cooling at 0.25 K/min to room temperature).

d) High temperature rubbing

High temperature rubbing was performed following the procedure described in the literature. 12 For the rubbing experiments thin films were prepared by doctor-blading from a 8 mg/ml CB solution. For the alignment of the films, a home-made rubbing machine was used in a glove box (Plas-Labs Inc.) under nitrogen atmosphere. It is composed of a rotating cylinder (4 cm diameter) covered by a microfiber cloth. The rubbing is performed by applying the rotating cylinder with a 2 bar pressure on the translating sample holder (1 cm/s). The sample holder can be heated at controlled temperatures during the rubbing process. The sample temperature is allowed to equilibrate for 1-2 min before rubbing. In the following, R designates the rubbing direction. Post-alignment thermal annealing was done in a THMS600 Linkam hot stage under nitrogen atmosphere at the required temperature for 1 min. Heating and cooling rates were 20 K/min and 0.5 K/min, respectively. e) Structural analysis TEM: Oriented areas were identified for TEM analysis by optical microscopy (Leica DMR-X microscope). The polymer films were coated with a thin amorphous carbon film and removed from the glass substrate by floating on a diluted aqueous HF solution (5 wt%) and subsequently recovered on TEM copper grids. TEM was performed in bright field, high resolution and diffraction modes using a CM12 Philips microscope equipped with a MVIII (Soft Imaging System) Charge Coupled Device camera. Calibration of the reticular distances in the ED patterns was made with an oriented PTFE film.

Molecular modelling was performed on a Silicon Graphic station using the Cerius2 program (Accelrys). A trial-and-error procedure was used to refine the crystal structure of PCPDTBT and F-PCPDTBT, following the same methodology as used previously to refine the crystal structures of P3HT, PF8 and poly(3-hydroxy-p-methylphenylvalerate) 15,25,26 as well as some conjugated co-oligomers 27 . For each step of the trial-and-error method, the molecular geometry was optimized using the "clean" procedure of the Cerius2 3.0 Program.

The starting point of the CPDT-BT monomer structure was obtained from the published structure of the oligomer CPDT-BT-CPDT. 28 For the single crystal diffraction calculations, a thickness of 30 nm was used. A 10% intensity threshold was used for the calculations of the fiber patterns using a precision symmetry (additional information on this procedure is available in the User's guide on Modeling Environment).

Results and discussion.

Lamellar crystals of form I of PCPDTBT and F-PCPDTBT.

Solvent vapor annealing of PCPDTBT and F-PCPDTBT in CB, hereafter called CBannealed films, resulted in thin films with highly crystalline domains as illustrated in Figure 1.

The polymorph obtained under these conditions is named form I for both polymers. Overall the [0 0 1] patterns of F-PCPDTBT bear striking similarity with that of -PF8 crystals (see Figure 7 of reference 15). In -PF8, chains form dimers that are arranged in an orthorhombic unit cell. The corresponding pattern of PF8 reflects the following arrangement: it shows the reflections associated with the overall packing of the dimers in the unit cell (corresponding to large reticular distances, typically > 10Å), and two intense reflections corresponding to the inter-chain distance in the dimer (around 5Å). The ED patterns of PCPDTBT and F-PCPDTBT show similar characteristics. They consist of a set of 6 intense reflections in a quasi-hexagonal lattice with reticular distances in the range of 9-11Å and a set of two intense reflections indexed as ±1 5 0 and ±3 1 0 for PCPDTBT and F-PCPDTBT, respectively. These characteristics suggest a high symmetry packing of chains into dimers with short 3.6-3.8 Å -stacking distance (in PF8 and PF7 no -stacking is evidenced in the dimers). Although both polymers imply a pairing of chains into dimers, the arrangement of the dimers in the unit cell are different for F-PCPDTBT and PCPDTBT. First, both structures show slightly different unit cell parameters (see Table 1). Second, the intense reflections corresponding to the inter-chain distance in the dimer are differently indexed. As demonstrated in our structural modelling below, the plane of the conjugated backbone is parallel to the a-axis for PCPDTBT and to the b-axis for F-PCPDTBT. This first result is remarkable and shows that the substitution of a single hydrogen atom by fluorine in the backbone of the polymer modifies significantly the packing of polymer chains in the crystal of form I. Further structural differences between PCPDTBT and F-PCPDTBT will be highlighted from the structural modeling (vide infra).

In-plane orientation of PCPDTBT and F-PCPDTBT chains.

To propose a valid structural model and in particular to establish the stacking mode between BT and CPDT in the dimers, characteristic fiber patterns showing multiple 00l reflections are needed. They were obtained from highly aligned films prepared by high-T rubbing or melt-crystallization of the polymers on friction transferred PTFE substrates. The ED patterns in Figure 2 of both the rubbed F-PCPDTBT and the epitaxied PCPDTBT film on PTFE are very detailed with numerous layer lines (up to the 10 th ). For each of the two polymers, the observed reflections can be clearly attributed to the form I evidenced in the CB-annealed films. In F-PCPDTBT, three major reflections of form I appear on the meridian: the 0 2 0 reflection at 10.55 Å, a 1 1 0 reflection at 9.7 Å and the 3 1 0 reflection at 3.7 Å (Supporting Figure S1). In PCPDTBT, two dominant equatorial reflections of form I are observed: the 1 1 0 at 10.5 Å and the 1 5 0 at 3.7 Å. The presence of several hk0 reflections on the equator indicates that the rubbed and epitaxied films have a typical fiber symmetry such that c PCPDTBT // c PTFE and c F-PCPDTBT //R. Of importance for the subsequent structural analysis is the intensity distribution of the reflections along the chain direction. Along the meridian of the ED patterns, strong reflections are observed on the 4 th , 6 th and 10 th layer lines of PCPDTBT and on the 4 th and 10 th layer line of F-PCPDTBT (a few more diffuse and weak reflections exist on intermediate layer lines).

In both patterns, the most intense meridional reflection is observed at 5.9 Å in PCPDTBT and 5.8 Å in F-PCPDTBT. It corresponds to the 0 0 4 reflection of form I. Thus, the patterns allow to extract the c axis parameter for both polymers : c=23.6±0.5Å for PCPDTBT and c=23.2±0.5 Å for F-PCPDTBT. Most importantly, no (0 0 2n+1) reflection is present on the meridian.

To conclude, the oriented fiber patterns of both polymers yield additional important structural informations that will be used for the subsequent structural refinement of form I dealing with the relative arrangement of the polymer chains along the chain direction.

Moreover, they allow to complete the unit cell parameters of form I determined from the [0 0 1] zones in CB-annealed samples. Table 2 summarizes the unit cell parameters for the form I of F-PCPDTBT and PCPDTBT.

Table 2. Lattice parameters for the orthorhomic form I of PCPDTBT and F-PCPDTBT and their calculated densities r calc . Z is the number of repetition units (CPDTBT) per unit cell. The absorption spectrum of form I of PCPDTBT is characterized by two dominant components at 680 nm and 740 nm (see Figure 3a, blue line). 22 The melt-annealed PCPDTBT film on PTFE shows a very similar absorption spectrum (see Figure 3 a, black line). On the other hand, films prepared by following the device processing protocol from literature, i.e.

spin coating from CB solution with 2w% DIO as solvent additive (hereafter called CB/DIOfilms), reveal a strong 800 nm band and a shoulder at 740 nm. In the literature [18][19][20] , the 800 nm band has been correlated with the presence of long range -stacking within an edgeon morphology, in analogy to P3HT. Temperature-dependent absorption and photoluminescence spectra and a detailed Franck-Condon analysis proved the aggregated nature of these films. 29 We suggest that the absence of the 800 nm absorption band in form I films can be explained by the absence of any long-range -stacking in the CB-annealed and the melt-annealed aligned films. The structural analysis further supports this finding (vide infra).

In the case of F-PCPDTBT, the same trend is visible: CB/DIO-films show a distinct absorption maximum at 800 nm whereas both the spectrum of the CB-annealed and the high temperature rubbed films are notably blue-shifted (see Figure 3). This suggests that two polymorphs can also be obtained in F-PCPDTBT: one that is described in the literature as due to -stacking and form I which is comparable to PCPDTBT. In literature all absorption spectra of F-PCPDTBT films show the characteristic 800 nm absorption. It is suggested that in F-PCPDTBT the 800 nm band is also correlated to an edge-on morphology comprising a long range -stacking similar to that in PCPDTBT. 23 This is further supported by GIWAXSresults by Jen et al. 30 Interestingly, simple spin coating from CB already results in similar spectra as the CB/ DIO-films. It was suggested that this is due to a stronger stacking tendency of F-PCPDTBT as compared to PCPDTBT. 23 Both TEM and UV-vis spectroscopy demonstrate that several preparation protocols (melt-annealing, HT-rubbing and solvent vapor annealing) all lead to the same polymorph, i.e.

form I which involves pairing of chains into dimers. The fact that slow crystallization methods such as melt-crystallization or solvent vapor annealing lead to the form I polymorph suggests that it is the thermodynamically stable structure and not a solvent-induced structure.

Structural models of form I.

First, it is worth to stress that, although sophisticated methods of crystallization were used for both polymers, the number of reflections extracted from the ED patterns is much more limited than for -conjugated polymers such as P3HT or polyfluorenes (PFO and PF2/6). This sets a strong limitation on the details that can be extracted from the ED patterns.

For instance, the exact side chain conformation cannot be determined precisely but only an approached conformation that yields the required electronic density distribution in the unit cell to properly account for the observed ED patterns. The side chain conformation shown in the refined models is only tentative but must be included in order to reproduce correctly the intensities in the 00l layers of the fiber patterns. In addition, the structural models use only one conformation of the 2-ethylhexyl side chain whereas four stereoisomers of the CPDT monomer (SS, RR, and two SR) should be present in the chains. For the structural modeling, we have chosen arbitrarily the SS conformation of the monomer (the choice of the stereoisomer was found to impact only marginally the calculated intensities of the reflections in the ED patterns).

In our previous work 22 , a first tentative model of form I PCPDTBT without sidechains was proposed based on the sole [0 0 1] pattern, i.e. with no information on the relative arrangement of the chains along the chain direction contained in the fiber patterns. With the addition of the newly obtained fiber patterns, the different ED patterns can be used for the determination of the space group by establishing the selection (extinction) rules. For the form I of both polymers, the same set of selection rules was determined:

(h 0 0) with h =2n (0 k 0) with k=2n, (h k 0) with h+k=2n and (0 0 l) with l=2n.

These rules are compatible with several orthorhombic space groups. To mention but a few: P n 2 n, P n c n, C c c 2 and P c c n. [START_REF]International Tables for Crystallography[END_REF] The first space group generates 4 asymmetric units in a unit cell contrary to 8 for the latter two. Given the refined unit cell parameters, 8 asymmetric units, i.e. 8 monomers must be present in the unit cell to obtain a reasonable crystal density around 1 g/cm³. Therefore, the space groups with superior symmetry P n c n, C c c 2 and P c c n are considered hereafter (the lower symmetry group P n 2 n group was retained in our previous study because, in the absence of information along the chain direction, a set of two monomers in trans conformation was used). The fiber patterns allow to further discriminate between these three space groups. Indeed, in the case of the C c c 2 group, the arrangement of the chains in the unit cell corresponds to a segregated stacking of BZ and CPDT units (see Figure S3). In C c c 2 symmetry, the relative arrangement of the chains in the unit cell is such that the alkyl chains are located around 0 0 2 planes. Such a packing would result in a strong 0 0 2 reflection in the fiber patterns. However, the experimental fiber patterns do not show any 0 0 2 reflection, thus ruling out the C c c 2 space group. Therefore, only the P n c n and P c c n space groups are retained. These two space groups lead to two radically different molecular packings of the chains in the dimers as illustrated in Figure S3. Several arguments allow to retain the dimer conformation obtained for the P c c n space group, i .e. the segregated stacking mode of BT and CPDT. First, the models with a P n c n symmetry leading to the best agreeement between calculated and experimental ED patterns correspond to a mixed stacking of BT and CPDT units which results in unrealistic short interatomic contacts between the chains in the dimer. Second, a strong argument for the proposed model with P c c n symmetry concerns the arrangement of BTs in the dimers. A recent study on a CPDT-BT-CPDT oligomer has demonstrated a faceto-face stacking of the BT units. 28 The choice of the P c c n space group is further important since it allows the backbones of PCPDTBT and F-PCPDTBT to -stack despite the presence of the sterically-demanding 2-ethylhexyl side chains. Let us analyze the major structural features of both models. First, we observe that the backbones of both PCPDTBT and F-PCPDTBT can be considered as planar although a small dihedral angle between the planes of CPDT and BT might be possible (in the CPDT-BT-CPDT oligomer, the BT and CPDT units are not perfectly copolanar 28 ). Second, for both polymers, the chains form dimers with a segregated stacking of CPDT and BT. The evidence

Conclusion.

Two distinct polymorphs (form I and form II) for PCPDTBT and F-PCPDTBT have been observed that differ from the structure observed in spin coated films from CB solution with 2w% DIO that are used in photovoltaic devices. The refined structures of form I are distinct from the classical layered structure where layers of -stacked backbones alternate with layers of alkyl side chains. In addition to form I, electron diffraction gives evidence for a second polymorph (form II) which is a priori isostructural for PCPDTBT and F-PCPDTBT.

Form I has been obtained by various crystallization methods, i.e. SVA, melt-crystallization on oriented PTFE or high-T rubbing, indicating that it is a thermodynamically stable structure that is not induced by a specific solvent. The characteristic UV-vis absorption signature of this stable form has been determined for both polymers. The hk0 and fiber-like ED patterns were used to generate tentative structural models of form I for both polymers. Form I involves pairing of chains into dimers arranged in an orthorhombic lattice (space group P c c n) with a pseudo-hexagonal symmetry. For both, PCPDTBT and F-PCPDTBT, a segregated stacking of BT and CPDT units is uncovered with BT units in anti-parallel face-to-face configuration.

Our modeling suggests that the backbones of PCPDTBT and F-PCPDTBT are essentially planar, although a small twist between successive monomers cannot be fully excluded.

Despite fairly similar unit cell parameters, the dimers of PCPDTBT and F-PCPDTBT are differently oriented in the unit cells leading to two distinct structures. These results demonstrate that a single H/F substitution in the backbone of a conjugated polymer can

Figure for title of content 3

 3 Figure for title of content

Scheme 1 .

 1 Scheme 1. Chemical structures of PCPDTBT and F-PCPDTBT.

  bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3benzothiadiazole)] (PCPDTBT) was purchased from 1-Material. The M w is 23 kg/mol with a PDI of 1.7 as measured by HT-SEC (160°C, trichlorobenzene, against PS standards). Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(5-fluoro-2,1,3-benzothiadiazole)] (F-PCPDTBT) was synthesized by the group of S. Janietz at the Fraunhofer Institut für Angewandte Polymerforschung in Potsdam. A molecular mass of M w = 10.8 kg/mol and a PDI of 1.6 was obtained by HT-SEC (160°C, trichlorobenzene, against PS standards). All solvents (chlorobenzene, CHCl 3 ,) were purchased from Sigma Aldrich (p.a. grade) b) Solvent vapor annealing

  Representative Selected Area Electron Diffraction (SAED) patterns of flat-on morphologies are shown in Figure 1.c and 1.d (the corresponding BF areas are shown in Figure 1.a and 1.b)for PCPDTBT and F-PCPDTBT respectively. PCPDTBT forms terrace-like flat-on features whereas F-PCPDTBT yields more elongated fiber-like flat crystals (FigureS2). (see BF image in Fig.1.b). SAED yields for both polymers well defined ED patterns with high symmetry and rather sharp reflections. However, the F-PCPDTBT patterns always display sharper reflections than PCPDTBT. From the flat-on morphology of the diffracting areas, we infer that the ED patterns correspond to domains with standing chains, i.e. the ED patterns correspond to the [0 0 1] zone. Accordingly, both ED patterns can be indexed using the parameters : a=12.4 Å and b=19.3 Å for PCPDTBT and a=11.0 Å and b=20.6 Å for F-PCPDTBT.

Figure 1 .

 1 Figure 1. Bright field images (a, b), experimental ED patterns (c, d) and calculated ED

Figure 2 .

 2 Figure 2.a and 2.c show BFs and the corresponding fiber-like patterns (Figure 2.b and

Table 1 .Figure 2 .

 12 Figure 2. Bright field images (a and b), experimental ED patterns (c and d) and calculated ED

3 . 3

 33 Absorption spectra of different polymorphs.The previous structural investigations by ED indicate that form I of PCPDTBT and F-PCPDTBT can be generated either by solvent vapor annealing in CB, high-T rubbing and melt-crystallization on PTFE substrates, although with different morphologies and orientations of crystalline domains on the substrates. UV-vis absorption spectroscopy is used to further confirm this result.

Figure 3

 3 Figure 3 Absorption spectra of thin films prepared by different techniques. a) PCPDTBT absorption

Figure 4

 4 Figure4shows the projections of the refined crystal structures of PCPDTBT and F-

  of a specific pairing of PCPDTBT and F-PCPDTBT chains into dimers with segregated stacking is an interesting finding from several points of views. First, such a dimerization prevents long-range -stacking as observed in semi-conducting polymers such as P3HT or PBTTT for which chains can -stack over large length scales (for instance in micrometer-long crystalline nanofibrils formed in p-xylene or anisole). This should also have implications on charge transport in such polymers. Second, the dimers are packed in an orthorhombic unit cell with b2a i.e. close to a hexagonal packing. This suggests that dimers may form first in solution and assemble afterwards in a hexagonal lattice when the films are in a swollen state in the presence of chlorobenzene. Finally, upon deswelling of the films, the unit cell becomes orthorhombic because of the side chain ordering. It is in this final step that the structures of F-PCPDTBT and PCPDTBT differ. Despite fairly close unit cell parameters, a remarkable difference in the packing of the dimers in the unit cells of PCPDTBT and F-PCPDTBT is observed: the backbone plane is parallel to (a,c) in PCPDTBT and (b,c) in F-PCPDTBT. It is however yet unclear how such a strong difference in the packing of the dimers can be linked to the presence/absence of a single fluorine atom in the backbone of the polymer. The [0 0 1] experimental pattern of F-PCPDTBT shows a characteristic streaking along 3 k 0 (see Figure 1.e) (mainly visible for the 3 1 0 reflection). Similar streaked features were observed previously in single crystal ED patterns of syndiotactic polypropylene (sPP) under certain crystallization conditions and/or tacticity of the polymer. Streaking in sPP crystals is observed along h 1 0. It is characteristic of stacking defects corresponding either to extended rows of chains displaced by b/4 or to groups of such rows displaced by b/4.[START_REF] Lotz | [END_REF]33 In F-PCPDTBT, the streaking is observed essentially for the 3 1 0 and 3 3 0 reflections. It is absent from other layer lines. Therefore, it is proposed that this streaking arises from disorder in the chain arrangement within the dimers rather than disorder in the packing of the dimers in the crystal. In PCPDTBT structural disorder does not result in streaking but rather in a blurring of the 1 5 0 and 4 2 0 reflections. It is considered as a fingerprint of structural disorder within the PCPDTBT dimers.Disorder in the arrangement of PCPDTBT and F-PCPDTBT is not unexpected when considering the recent structural investigations on a cyclopentadithiophene-benzothiadiazole oligomer.28 Indeed, the thiadiazole tip of the BT unit was found to point equiprobably in two possible directions in the crystal of this oligomer. In the case of F-PCPDTBT, this would mean that the sulfur tip of BT could point either along b or -b in the absence of strong steric hindrance by the surrounding alkyl side chains. A further source of disorder in both polymers is related to the coexistence of four stereoisomers (RR, RS, SR and SS) of CPDT since the 2ethylhexyl side chain contains an asymmetric carbon. These four stereoisomers are expected to occur at random in the chains, leading expectedly to some packing disorder of the chains within the dimers.

Figure 4 . 3 . 4 .Figure 5 )

 4345 Figure 4. Projections along the a,b and c unit cell axes of the structural models refined from

Figure 5 .

 5 Figure 5. a) and b) show ED patterns taken from the highly crystalline almost transparent

significantly affect the chain packing in the crystal structure. As opposed to form I, the unit cell of form II contains two chains that are not paired as dimers.

ASSOCIATED CONTENT

Supporting information.

Enlarged electron diffraction pattern of F-PCPDTBT, microscopy images of CB-annealed F-PCPDTBT samples, comparison of the stacking of CPDT and BTZ unit in a dimer of PCPDTBT for the structures with different space groups, comparison of the calculated [0 0 1] patterns for the form I of F-PCPDTBT taking or not taking into account the 2-ethylhexyl side chains. PDB files of the refined structural models of PCPDTBT and F-PCPDTBT.

AUTHOR INFORMATION

Corresponding authors: * E-mail : Martin.brinkmann@ics-cnrs.unistra.fr sabine.ludwigs@ipoc.uni-stuttgart.de + Present Address: College of Nanotechnology, King Mongkut's Institute of Technology Ladkrabang (KMITL), Bangkok, 10520, Thailand

ACKNOWLEDGMENTS.

M. B. acknowledges financial support by the European commission under contract Interreg

Rhin-Solar (C25). We thank Silvia Janietz for synthesizing and giving us the F-PCPDTBT material. P. Martinoti is acknowledged for supplying the Plas-Labs glovebox. M. Schmutz and C. Blanck are acknowledged for technical support in TEM. Bernard Lotz is gratefully acknowledged for fruitful discussions. FF, DT and SL thank the DFG for funding within the priority program "Elementary processes in organic solar cells" (SPP1355) and the Emmy Noether Program.


Shashank Mishra
email: shashank.mishra@ircelyon.univ-lyon1.fr

Erwann Jeanneau

Liang Tian

Ioana Nuta

Elisabeth Blanquet

Deobrat Singh

Rajeev Ahuja

Catherine Marichy

Stéphane Daniele

Asymmetry-Induced Redistribution in Sn(IV)-Ti(IV) Hetero-Bimetallic Alkoxide Precursors and Its Impact on Thin-Film Deposition by Metal-Organic Chemical Vapor Deposition

come

have become the predominant single-source precursors for oxide-based ceramic materials, mainly through sol-gel processing and MOCVD, respectively, because of their commercial availability, high solubility in routinely used organic solvents, and easy tunability of their hydrolytic characteristics and mass-transport properties. [START_REF] Bradley | Alkoxo and Aryloxo derivatives of Metals[END_REF][START_REF] Turova | The Chemistry of Metal Alkoxide[END_REF][START_REF] Condorelli | Engineering of molecular architectures of βdiketonate precursors toward new advanced materials[END_REF][START_REF] Tiitta | Volatile Metal β-Diketonates: ALE and CVD Precursors for Electroluminescent Device Thin Films[END_REF] Another important axis of the molecular engineering is the synthesis of bi-and higher metallic derivatives with appropriate properties. [START_REF] Gahlot | Molecules versus nanoparticles: Identifying a reactive molecular intermediate in the synthesis of ternary coinage metal chalcogenides[END_REF][START_REF] John | Synthesis of Heterometallic Compounds with Uncommon Combinations of Elements for Oxide Nanomaterials Using Organometallics[END_REF][START_REF] Chen | Direct synthesis of hexagonal NaGdF4 nanocrystals from a single-source precursor: Upconverting NaGdF4:Yb 3+ ,Tm 3+ and its composites with TiO2 for near-IR-driven photocatalysis[END_REF][START_REF] Wei | Volatile Heterometallic Precursors for the Low-Temperature Synthesis of Prospective Sodium Ion Battery Cathode Materials[END_REF][START_REF] Mishra | A single source precursor route to group 13 homo-and heterometal oxides as highly active supports for gold catalyzed aerobic epoxidation of t-stilbene[END_REF][START_REF] Mishra | Novel heterometal-organic complexes as first single source precursors for up-converting NaYF4:Yb 3+ , Er 3+ /Tm 3+ nanomaterials[END_REF][START_REF] Mishra | Aminoalkoxo-supported heteroleptic hexanuclear gallium(III) wheel as a synthon for group 13 heterometallics: A rare sol-gel precursor for mixed Al-Ga oxide as a support for gold catalysts[END_REF][START_REF] Mishra | Heterometallic Na-Y(Ln) trifluoroacetate diglyme complexes as novel single source precursors for upconverting NaYF4 nanocrystals co-doped with Yb and Er/Tm ions[END_REF] These single-source precursors simultaneously provide two or more metals in an accurate stoichiometry, allowing complex ceramic materials to be generated in one step by eliminating the prerequisite of matching the reaction rates in a multicomponent precursor mixture. [START_REF] Lu | The use of mixed-metal single source precursors for the synthesis of complex metal oxides[END_REF][START_REF] Schubert | Heterobimetallic sol-gel precursors and intermediates[END_REF][START_REF] John | Synthesis of Heterometallic Compounds with Uncommon Combinations of Elements for Oxide Nanomaterials Using Organometallics[END_REF][START_REF] Matthews | Structure, photochemistry and applications of metal-doped polyoxotitanium alkoxide cages[END_REF][START_REF] Szafert | Well-defined polynuclear heterobimetallic complexes as precursors for ceramic and magnetic materials[END_REF] Among the various properties desired in MOCVD precursors, the most important ones are the high volatility and good thermal stability for efficient transport, as well as high reactivity to easily obtain the desired material. [START_REF] Hatanpää | Precursors as enablers of ALD technology: Contributions from University of Helsinki[END_REF][START_REF] Emslie | Metal ALD and pulsed CVD: Fundamental reactions and links with solution chemistry[END_REF][START_REF] Potts | Bis(cyclopentadienyl) zirconium(IV) amides as possible precursors for low pressure CVD and plasma-enhanced ALD[END_REF] One of the important tactics to enhance volatility is to introduce heterolepticity in the molecules, which usually makes them loosely packed in the lattice and hence more volatile. However, the impact of the asymmetric structure of a bi-metallic precursor on its volatility as well as the composition and the quality of the deposited material is poorly studied.

Previously, we have reported synthesis of a heterometallic derivative [SnCl4(µ-OEt)2Ti(OEt)2(HOEt)2] (A) in quantitative yield by a convenient reaction between commercially available reagents SnCl4 and Ti(OEt)4. [START_REF] Mishra | A convenient and quantitative route to Sn(IV)-M [M = Ti(IV), Nb(V), Ta(V)] heterobimetallic precursors for dense mixed-metal oxide ceramics[END_REF][START_REF] Mishra | Novel heteroleptic heterobimetallic alkoxide complexes as facile single source precursors for Ta 5+ -doped TiO2-SnO2 nanoparticles[END_REF] This work was motivated by the potential usefulness of the TiO2-SnO2 system as eco-friendly oxide-based thermoelectric materials. [START_REF] Dynys | Thermoelectric Properties of Undoped and Doped (Ti0.75Sn0.25)O2[END_REF][START_REF] Hochepied | Aqueous Coprecipitated Ti0.5Sn0.5O2 Nanopowders as Precursors for Dense Spinodally Decomposed Ceramics[END_REF] Besides, the mixed tin-titanium oxides are also promising materials for the photovoltaic and photocatalytic applications. [START_REF] Xu | Fabrication of one-dimensional heterostructured TiO2@SnO2 with enhanced photocatalytic activity[END_REF][START_REF] Ponja | Aerosol assisted chemical vapour deposition of hydrophobic TiO2-SnO2 composite film with novel microstructure and enhanced photocatalytic activity[END_REF][START_REF] Shinde | 2 nanowall-arrays coated with rutile-TiO2 nanoneedles for high performance dye-sensitized solar cells[END_REF] While the use of above single-source single molecular precursors in sol-gel process ensured the synthesis of mixed nanoparticles of rutile Ti0.5Sn0.5O2 without the generation of pure SnO2 grains (which are hard to be sintered to high density) and thus allowing complete densification at low temperature by the spark plasma sintering (SPS) process, the spinodal decomposition in the TiO2-SnO2 system produced nanoscale TiO2/SnO2-rich lamellae, where the high density of the well-organized interfaces reduced the thermal conductivity of the ceramic. To make above Sn-Ti heterometallic complexes more suitable for deposition by MOCVD method, we have now modified it with a sterically hindered β-diketonate (2,2,6,6-heptane-3,5-dione, abbreviated as thdH) to obtain a couple of novel molecular precursors and studied their thermal and vapor pressure behavior to assess the suitability of these complexes as precursors for the vapor phase production of TiO2-SnO2, Ti-doped SnO2 or Sn-doped TiO2 thin films.

The reaction of SnCl4 with Ti(OEt)4 provides a practical and quantitative approach to a heterobimetallic Sn(IV)-Ti(IV) derivative with the simple addition formula [SnCl4(µ-OEt)2Ti(OEt)2(HOEt)2] (A), [START_REF] Mishra | A convenient and quantitative route to Sn(IV)-M [M = Ti(IV), Nb(V), Ta(V)] heterobimetallic precursors for dense mixed-metal oxide ceramics[END_REF] which in subsequent reactions in toluene with 2,2,6,6-heptane-3,5dione (thdH) in 1:1 and 1:2, stoichiometry gives access to heteroleptic mixed species of alkoxo-βdiketonato, [SnCl4(µ-OEt)2Ti(thd)(OEt)(HOEt)] (1) and [SnCl4(µ-OEt)2Ti(thd)2] (2), respectively (Scheme 1). Both compounds are highly soluble in chloroform, dichloromethane and ethanol, but show slightly less or poor solubility in toluene and n-pentane, respectively. Given the simple addition nature of the obtained products and excellent yield (typically above 90%), these reactions are easily scalable to the multigram scale. It assumes importance in view of large amounts (typically 5-10 g) of precursors needed for optimizing vapor pressure measurements and film deposition processes. These compounds are also more stable to moisture than the precursor compound A. At higher temperatures, however, compound 1 rearranges to produce a mixture of A and 2, as shown by the isolation and structural characterization of the solvated dichloromethane species [SnCl4(µ-OEt)2Ti(thd)2]•CH2Cl2 (2a) from the products obtained after 1 was maintained at 80°C for a few hours, followed by crystallization from dichloromethane. The new compounds were thoroughly characterized by elemental analysis, spectroscopic (FT-IR, [START_REF] Brune | Influence of the Choice of Precursors in the Synthesis of Two Dimensional Transition Metal Dichalcogenides[END_REF] H and 119 Sn NMR) and single crystal X-ray diffraction (XRD) studies. While solvated species 1 showed broad absorption and weak shoulder in the region 3200-3400 cm -1 and 1660 cm -1 for ν O-H and δ O-H, respectively, the absence of such absorption bands in the FT-IR spectra of 2 and 2a confirmed the formation of non-solvated species. The FT-IR spectra of 1, 2 and 2a exhibited characteristic bands of the alkoxy and β-diketonate groups attached to the metal in the 1200-400 cm -1 region (Figure S1). Although the room temperature 1 H NMR spectra of these complexes were deceptively simple due to their fluxional behaviour, they confirmed the integration ratio between the ethoxide and heptanedionate ligands. The 119 Sn NMR of 1, 2 and 2a showed only a sharp peak at δ -548 to -600 ppm, which was consistent with values in the literature for the 6-coordinate Sn(IV) centre. [START_REF] Verchère | Heteroleptic Tin(IV) Aminoalkoxides and Aminofluoroalkoxides as MOCVD Precursors for Undoped and F-Doped SnO2 Thin Films[END_REF][START_REF] Mishra | Synthesis and spectroscopic (IR, 1 H, 13 C, and 119 Sn NMR) characterization of mono-and diorganotin(IV) complexes containing sterically hindered Narylsalicylaldiminate groups[END_REF] The molecular structures of [SnCl4(µ-OEt)2Ti(thd)(OEt)(HOEt)] ( 1) and [SnCl4(µ-OEt)2Ti(thd)2] (2) consist of Sn(IV) and Ti(IV) six-coordinated centres bridged by two ethoxo groups (Figure 1). Except for the fact that the complex 2a crystallizes with a solvated dicloromethane molecule, the molecular structure of the 2 and 2a are quite similar. Therefore, structure of 2a is presented in Supporting Information only (Figure S2). The overall molecular geometry of all these structures can be described as a fusion of two octahedra built about Sn(IV) and Ti(IV) via a common edge (O1 and O2). The six-coordination sphere around the titanium atom consists of all oxygen atoms, whereas the tin atom has a O2Cl4 environment. The Ti-O distances in 1, 2 and 2a vary from 1.742 (4) to 2.075(4) Å, the bond involving terminal OEt groups in 1 Thermogravimetric analysis was used to estimate the thermal stability and volatility of the new precursors and to provide a first validation of the potential use of these metal-organic precursors for MOCVD (Figure 2a). The curves for compounds A and 1 had common characteristics with an onset of weight loss at low temperature (around 100°C) and residues of 40% and 25%, respectively (as compared to theoretical residues of 40 and 34% for SnTiO4). These data demonstrated very low thermal stability and non-volatility of these two compounds. Compound 2 exhibited higher thermal stability (up to 200 °C), which is usually the case when β-diketonate ligand is added in the metal coordination sphere. Nevertheless, with a 40% final residue, it did not appear that the volatility of the modified precursor improved a lot. These studies indicated that the thermal characteristics of the new precursors at atmospheric pressure are not very favorable for their use in the conventional MOCVD. In order to more accurately assess the volatility of the compounds, vapor pressure studies were conducted on compounds A, 1 and 2. The vapor pressure values are given in the Supporting Information. Their temperature dependence (Figure 2b) is obtained by linear least-squares treatment of the data and fitted using the equation log (p/Pa) = A/(T/K) + B (Table 1). The results obtained show that the progressive addition of the thd ligand makes it possible to obtain increasingly volatile compounds 1 and 2. For [SnCl4(µ-OEt)2Ti(thd)(OEt)(HOEt)] ( 1), the change of the slope trend at about 373 K shows that it must be thermally unstable. Indeed, the difference in slope in Figure 2b for the temperature range 357-370 K suggested that it underwent a redistribution of ligands to transform into compound [SnCl4(µ-OEt)2Ti(thd)2] (2). Subsequent crystallization of the products from dichloromethane obtained after 1 was maintained at 80°C for a few hours and structural determination by single crystal X-ray studies, which showed the isolated species as the solvated dichloromethane species [SnCl4(µ-OEt)2Ti(thd)2]•CH2Cl2 (2a), further confirmed the above redistribution of 1 into A and 2 (Figure S3). Using van't Hoff equation, it was obtained the enthalpy of sublimation and the entropy of the studied precursors (Tables S2 andS3). The DFT calculations on the precursors provided further confirmation on above redistribution of 1 into A and 2. The optimized structures of these compounds showed geometrical parameters which were largely consistent with their single crystal X-ray data (see supplementary information, Table S1). The cohesive energy of reactant 1, calculated from the ab initio molecular dynamics (AIMD) simulations at 353 K, was found to be -4.33 eV/ atom, which is slightly less than the cohesive energy of the products of above redistribution (-4.37 eV/atom), indicating that the products were more stable than the reactant at 353 K. Although the vapour pressures obtained (around 0.1 Pa at 323 K) were slightly lower than the typical values used in MOCVD or ALD processes, [START_REF] Ritala | Handbook of Thin Film Materials[END_REF] the most volatile and stable compound 2 was tested in mixed TiO2-SnO2 thin-film deposition by CVD. Film deposition was performed at 330 °C on Si wafer or Si/SiO2 substrates under low pressure conditions with the precursor container maintained at 150 °C. The Scanning Electron Microscopy (SEM) images of the deposited films exhibited a nano-structured granular layer that was not dense but uniformly covered and continuous (Figure 3). Depending upon substrate's position in the reactor and deposition time, the film thickness varied in the range 10-170 nm, as indicated by the ellipsometry measurements (please see Supporting Information for more details). However, XRD and Energy-Dispersive Xray spectroscopy (EDX) studies at different points in the film showed varying Ti and Sn ratio with the compositions changing in the range Ti0.33Sn0.66O2 to SnO2 (one particular XRD is displayed as Fig. 3c). For gaining a deeper knowledge of the composition and chemical state of the elements present, X-ray photoelectron spectroscopy (XPS) studies were conducted on a representative sample (Fig. 3d-f). The survey spectra revealed that besides containing tin, titanium and oxygen, these films also had a high carbon content upto 28% because of incomplete decomposition of the precursor. Quantitative analysis of the sample revealed an Sn/Ti stoichiometry close to 2. In the core level spectra, the presence of Ti 4+ is indicated by the binding energies at 458.4 eV and 464.2 eV, due to Ti 2p3/2 and Ti 2p1/2, respectively, [START_REF] Gahlot | Room-temperature conversion of Cu2-xSe to CuAgSe nanoparticles to enhance the photocatalytic performance of their composites with TiO2[END_REF][START_REF] Gahlot | Precursor-mediated synthesis of Cu2-xSe nanoparticles and their composites with TiO2 for improved photocatalysis[END_REF] whereas the electron binding energy (BE) value for Sn 3d5/2 appears at 486.6 eV, indicating the presence of an oxygen-deficient SnOx (with 2 ≥ x ≥ 1). These results suggest that the asymmetric structure of the bi-metallic compound led to a fragmentation of the molecule under CVD conditions (eq. 1), thus resulting in an asymmetry of reactivity with a multi-halogenated fragment being much more reactive than the fragment containing the β-diketonate ligands. Indeed, both Ti and Sn fragments have been employed

separately in CVD experiments for the deposition of TiO2 and SnO2, respectively. While the closely related compound [Ti(OPr i )2(thd)2] is commercially available and bench-mark precursor for the CVD deposition of TiO2, [START_REF] Bhakta | MOCVD of TiO2 thin films and studies on the nature of molecular mechanisms involved in the decomposition of [Ti(OPr i )2(tbaoac)2[END_REF] the tin fragment SnCl4 has also been employed frequently for the deposition of SnO2. [START_REF] Molloy | Precursors for the formation of tin(IV) oxide and related materials[END_REF] As the above Ti precursor requires higher temperature (~500 °C) than SnCl4, it is no surprise that under our CVD conditions (substrate temperature 330 °C) a majority of Ti-species is pumped off leaving behind Sn-rich films.

The AIMD calculations on 2 at 623 K further confirmed its dissociation into two homometallic components i.e. Ti(thd)2(OEt)2 and SnCl4, as indicated by high energy fluctuation for 2 below 4 ps in the Figure 4, which smoothens gradually after the dissociation (the dissociated SnCl4 shown in dotted red circle in Fig. 4). The associated negative dissociation energy (-0.83 eV) indicates exothermic nature of the reaction and, therefore, an energetically favorable transformation. 41 In conclusion, the thermal behavior of a series of bi-metallic Ti-Sn precursors was evaluated in terms of their molecular structure resulting from the progressive addition of the thd ligand. The thd ligand improved the volatility of the precursors but also generated a strong asymmetry in the structure, which is consisted of SnCl4 and Ti(thd)(OEt)(EtOH) or Ti(thd)2 fragments bridged through two ethoxo groups. During gas phase deposition, this structural asymmetry led to different reactivities of the two metallic fragments and the deposition of a tin-rich layer. These results show that having a volatile bimetallic precursor is not a guarantee of film homogeneity by MOCVD, as it is equally important to ensure that the reactivity of each metal center is not too different.

ASSOCIATED CONTENT

Supporting

Scheme 1 .

 1 Scheme 1. Synthesis of heteroleptic alkoxo-β-diketonato bimetallic Sn-Ti species and redistribution of 1 into A and 2.

[ 1 .Figure 1 .

 11 Figure 1. Perspective views of (a) [SnCl4(µ-OEt)2Ti(thd)(OEt)(HOEt)] (1) and (b) [SnCl4(µ-OEt)2Ti(thd)2] (2) with displacement ellipsoids drawn at the 30% probability level. H atoms are

Figure 2 .

 2 Figure 2. (a) TGA curves and (b) temperature variation of vapor pressure of [SnCl4(µ-OEt)2Ti(OEt)2(HOEt)2] (A) ( ), [SnCl4(µ-OEt)2Ti(thd)(OEt)(HOEt)] (1) ( ) and [SnCl4(µ-OEt)2Ti(thd)2] (2) ( ). The fit parameters of the linear trends are given in theTable 1. Erreur !

Figure 3 .

 3 Figure 3. Characterization of thin films deposited on Si wafers using the precursor 2: (a and b) Representative surface and cross-sectional SEM images, (c) XRD, and (d-f) XPS spectra.

Figure 4 .

 4 Figure 4. The ab initio molecular dynamics (AIMD) simulations of 2 at 623 K.

  Information Available. Experimental details of synthesis of new precursors, their characterization, vapor pressure measurements, MOCVD deposition and DFT calculations, FT-IR Laurence Burel (IRCELYON) for SEM images. D.S. and R.A. thanks the Swedish Research Council (VR-2016-06014 & VR-2020-04410) and J. Gust. Richert stiftelse, Sweden (2021-00665) for financial support. SNIC and HPC2N are acknowledged for providing the computing facilities.

Table 1 . Erreur ! Source du renvoi introuvable.Table 1 .

 11 Sublimation parameters from the vaporization of A, 1 and 2.

			Log (p/Pa) = A/(T/K) + B
	Precursor	T range /K
			A	B
	(A)	340 to 420	-1919 ± 232	3.869 ± 0.623

spectra of new precursors, single crystal structure of 2a, digital images of precursor 1 before and after heating as well as ellipsometry parameters on selected samples. This material is available free of charge via the Internet at http://pubs.acs.org.

Accession Codes

CCDC1558712, 1558713 and 1558714 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

The following files are available free of charge.

Cif files of 1, 2 and 2a (file type, i.e., cif) Supplementary information (file type, i.e., PDF)

AUTHOR INFORMATION

Corresponding Author

* Shashank Mishra, E-mail: shashank.mishra@ircelyon.univ-lyon1.fr; Fax : (+33) 472445399.

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT S.M. is grateful to (the late) Prof. R. C. Mehrotra, (the late) Prof. L. G. Hubert-Pfalzgraf and Prof.

A. Singh for introducing him to the fascinating world of metal alkoxides. Authors thank Ms.

FOR TABLE OF CONTENTS USE ONLY

Asymmetry

Synopsis

The introduction of sterically crowded thdH ligand in the Ti-Sn heterometallic precursors improves the volatility of the precursors significantly, but also generates a strong asymmetry in the structure, leading to different reactivities of the two metallic fragments during MOCVD and the deposition of a tin-rich layer.


Ziani Hanane

M 'hamed Kaid

Ikhou Djamila

Abdelkader Ammam

D Villemin

Preparation, characterization and antibacterial applications of ZnAl-LDH with the diaminododecylphosphonic acid intercalation

Layered double hydroxides (LDHs) have been widely investigated in a wide range of applications in health, in the pharmaceutical industry and in the material of biotechnology industries. This material can be considered as a group of promising materials in the development of new health applications. The combination of phosphonic acid with LDHs material create a new hybrid material with new properties.In this work the synthesis of Zn/Al double layered hydroxides by chemical co-precipitation method (molar ration 2) and grafted with Diamino Dodecyl Phosphonic Acid (DDPA) via anion-exchange mechanism. The samples were characterized and confirmed by X-ray diffraction (XRD), and the presence of diamino dodecyl phosphonic acid (DDPA ) was verified by Elemental analysis, BET analysis, and infrared spectroscopy. Both of the samples were found to be showing antibacterial activity. The zone diameters of Zn-Al-LDH were 40 mm and 25 mm for Escherichia coli(ATCC 25922) and Streptococcus (ATCC 25922)and 20 mm for bacillus (ATCC 25922) whereas the same for hybrid LDH (Zn-Al-DDPA) were43 mm , 32 mm and 25 mm for the same bacteria showing stronger antibacterial activity of the grafted material over the material itself. The experimental results confirm the application of Zn-Al-DDPA in the field of antibacterial activities and may offer a promising antibacterial elucidation to the society.

Introduction

Layered double hydroxides (LDHs) are one such potential inorganic matrices, containing sheets succession [START_REF] Kadari | Selective study of elimination of Cd (II) and Pb (II) from aqueous solution by novel hybrid material[END_REF] they are layered compounds by metal hydroxide sheet with positive charge and interlayer space filled with anion with negative electric charge. They can be expressed by the general formula [M II 1-x M III x (OH) 2 ] x+ [A n x/n . mH 2 O] x--. [START_REF] Cheng | A novel antimicrobial composite: ZnAl-hydrotalcite with phydroxybenzoic acid intercalation and its possible application as a food packaging material[END_REF]in which M 2+ (Mg 2+ , Ca 2+ , Zn 2+, Cu 2+ , Co 2+ , Ni 2+ , etc.) and M 3+ (Al 3+ , Fe 3+, Ga 3+ , Cr 3+ ) are divalent and trivalent cations and An - (Cl -, CO 3 2-, NO 3 -, etc)is an anion, thus having positive or negative charge layers [START_REF] Marcato | New hybrid material based on layered double hydroxides and biogenic silver nanoparticles: antimicrobial activity and cytotoxic effect[END_REF][START_REF] Totaro | Dual chain extension effect and antibacterial properties of biomolecules interleaved within LDH dispersed into PBS by in situ polymerization[END_REF].Depending up on the nature of cations and their molar ratios M(II)/M(III), and so the anions type, many compounds, with vast difference, can be obtained. The range 0.2 ≤x ≤ 0.33 is generally acknowledged to be suitable for the synthesis of LDH compounds i.e. the ratio of M 2+ /M 3+ is in between 2:1 to 4:1 (Mishra et al.,2013;[START_REF] Zümreoglu-Karan | Layered double hydroxidesmultifunctional nanomaterials[END_REF].These anionic clays, has been noticed to be of considerable uses due to their fascinating properties in compositional flexibility, anion and cation exchangeability, in many technologically in catalysis, separation technology, optics, medical science, low toxicity, superior biocompatibility, synthesis of films and coatings for anticorrosion, sensing and antibacterial applications [START_REF] Ryu | Layered double hydroxide as novel antibacterial drug delivery system[END_REF][START_REF] Chen | Self-assembled Fe 3 O 4-layered double hydroxide colloidal nanohybrids with excellent performance for treatment of organic dyes in water[END_REF][START_REF] Mei | A bottom-up synthesis of rare-earth-hydrotalcite monolayer nanosheets toward multimode imaging and synergetic therapy[END_REF]Mishra et al., 2018).

ZnAl hydroxides are effective antibacterial agents for bacteria such as Escherichia coli and Staphylococcusaureus due to the hydroxides (-OH) and the nature of the metallic cations, where Zn 2+ is one of the most active ones, due to its strong oligodynamic features [START_REF] Ferraris | Antibacterial titanium surfaces for medical implants[END_REF][START_REF] Gohi | Preparation of the hybrids of hydrotalcites and chitosan by urea method and their antimicrobial activities[END_REF]. Moreover, Zn ions possess excellent antibacterial ability and were widely used as inorganic antibacterial agents (Hue et al.,2013;[START_REF] Wang | The synergistic antibacterial activity and mechanism of multicomponent metal ions-containing aqueous solutions against Staphylococcus aureus[END_REF]. Also, many hybrid materials, organic hybrids, inorganic hybrids and organic-inorganic hydrids,have been tested and still have a lot ofl applications in biomedical science [START_REF] Gohi | Preparation of the hybrids of hydrotalcites and chitosan by urea method and their antimicrobial activities[END_REF].

. [START_REF] Wang | Intercalation of Ga3+-salicylidene-amino acid Schiff base complexes into layered double hydroxides: synthesis, characterization, acid resistant property, in vitro release kinetics and antimicrobial activity[END_REF] studied the antibacterial and the antimicrobial activity of Mg-Al-NO 3 -LDH with Ga 3+ salicylidene-amino acid Schiff base complex intercalation. [START_REF] Wang | Intercalation of Ga3+-salicylidene-amino acid Schiff base complexes into layered double hydroxides: synthesis, characterization, acid resistant property, in vitro release kinetics and antimicrobial activity[END_REF] In previous works, we have prepared and characterized a new hybrid material (ZnAl-DDPA) by intercalating the double layered hydroxide synthesized in our laboratory (ZnAl-LDH) prepared by coprecipitation method using diamino dodecyl phosphonic acid (DDPA). In this work, Streptococcus, Bacillus (gram negative) and E. Coli (gram positive) antibacterial activity has been studied using a synthesized LDH and its hybrid material.

Experimental

Materials

The reagents used in this study were Zn Al-Cl and ZnAl-DDPA synthesized in the laboratory [START_REF] Villemin | Rapid one-pot synthesis of alkane-α, ω-diylbisphosphonic acids from dihalogenoalkanes under microwave irradiation[END_REF][START_REF] Kadari | Selective study of elimination of Cd (II) and Pb (II) from aqueous solution by novel hybrid material[END_REF], the raw materials used were ZnCl 2 (Riedel-de Haën), AlCl 3 .6H2O (Panreac ) NaOH(99%, Riedel De Haen).

The bacterial stains used in this work are Streptococcus (ATCC 25922 gram negative) and Bacillus (ATCC 25922 gram negative) , E. Coli (ATCC25922 gram positive).

Methods

ZnAl-Cl Synthesis

The ZnAl-HDL with a molar ratio of 2 :1 was synthesized by the co-precipitation method. About 150 ml of ZnCl2.7H2O (0,66M) et de AlCl3.6H2O(0,33M) are added to an reactor initially containing 100 ml of distilled water at 25 °C under stirring. The pH of the reaction was maintained constant at 10.5±0.1 with the addition of 1.5 M NaOH solution under vigorous stirring. Duration of the reaction was 24 h at the ambient temperature (25°C). The precipitate obtained was washed and centrifuged several times and was dried at room temperature then crushed.

Synthesis of ZnAl-DDPA

The intercalation of the diamino dodecyl phosphonic acid (DDPA) was made by the method of exchange of ions by the direct reaction between the DDPA and ZnAl-Cl [START_REF] Feng | Synthesis and characterization of a UV absorbent-intercalated Zn-Al layered double hydroxide[END_REF] . The hybrid material was obtained by mixing the DDPA with ZnAl-LDH. Briefly, 1g of DDPA dispersion (1.736 × 10-3 M) is dissolved in 50 ml of water and mixed with 20 g for LDH [ZnAl-Cl] (Ratio 1/20). The reaction mixture is left under stirring for 24 hours. It is filtered and dried for 48 hours at the ambient temperature.

Characterization techniques 2.3.1. XRD Analyses

The X-ray diffraction (XRD) analysis was performed on a PAN analytical X'PERT Prodiffractometer with CuKa radiation( (1.5405 A°) and with an operating voltage of 40 kv and a sweeping of 2ufrom 5 to 100.

FTIR Analyses

Fourier-transform infrared (FTIR) spectra of the samples were obtained with a Perkin-Elmer Spectrum 16PCequipped with a thermostat. Specific surfaces areas and pore size were analyzed by the Brunauer Emmett Teller (BET) method. Measurements were made by adsorption and thermal desorption of N2 at 77°K and the results were collected by Quantachrome Autosorb-6.

BET analyses

Elementary analyses

Elementary analysis was carried out using a Shimadzu ICPS-7500 inductivly coupled plasma (ICP) atomic emission spectroscopy.

Antibacterial activity

ZnAl-Cl and Zn-Al-DDPA antibacterial activity was examined against three test organisms, namely E. coli (ATCC 25922), Streptococcus (ATCC 25922) and Bacillus (ATCC 25922), by qualitative method [START_REF] Mishra | Orientation of organic anions in Zn-Al layered double hydroxides with enhanced antibacterial property[END_REF]to evaluate the potency of each sample. 0,5 ml of cultures were diluted in 20 ml of Muller Hinton liquid, this last was melted by heating and then cooled before placing in contact with the bacterial suspension. One milligram of each sample was placed at well-marked places on bacterial culture. The mixture was deposited in Petri dishes of 90 mm in the form of wells.

The inhibition zones of each sample around spots at regular intervals after 24h incubation, at 37 °C, were noticed visually.

Results and discussion

X-ray diffraction

The XRD patterns of the hybrid (ZnAl-DDPA) and ZnAl-LDH are presented in the figure 2 ,The basal plane spacing of the pristine LDH (Zn/Al-LDH) is 7.55 A° and an inter metallic distance of 1.53 A°. With a successful intercalation there is an increase in the basal plane of ZnAl-DDPA caused by the intercalation of DDPA, herein the spots can be indexed to a rhombohedral symmetry (space group,R -3m) [START_REF] Mandal | Defluoridation of water using assynthesized Zn/Al/Cl anionic clay adsorbent: Equilibrium and regeneration studies[END_REF]andwere indexed in an hexagonal structure. The (a) and (c) lattice parameters were calculated using ( 110) and ( 003) reflections, respectively.

Fourier transformed infrared spectroscopy analysis (FTIR)

Bands of Fourier transformed infrared spectroscopy (FITR) are shown in Figure3, the band 3458 cm - 1 corresponds to the stretching vibration of the hydroxide groups of the molecules water, The peaks located at 1120 and 1020 cm -1 are attributed to the bending vibration of adsorbed phosphate P=O, P-O respectively [START_REF] Villemin | Rapid one-pot synthesis of alkane-α, ω-diylbisphosphonic acids from dihalogenoalkanes under microwave irradiation[END_REF], showing that the pristine LDH grafted by phosphonic acid (DDPA) and the secondly significant difference between the two spectra is that there are two peaks of low intensity recorded at 2980 and 2857 cm -1 which due respectively to the elongations of -CH 2 asymmetrical and symmetrical.

Elemental analysis and BET analysis

The molar ratio of the synthesized LDH materials was determined with use of AAS elementary analysis, and the results are given in Table 1, it can be distinguished that there are deviations between initial atomic ratios in solution and final atomic ratios were observed. It is observed from the data that some amount of Zn is being replaced by addition of DDPA to the system, and it is remarkable that the absence of Cl -in the composition of LDH hybrid (ZnAL-DDPA) proves the exchange of ions between the chloride ions and the DDPA. Specific surface areas of ZnAl-LDH and ZnAl-DDPA were estimated and presented in Table 2. It is evident from the table that the specific surface area (BET) decreased after DDPA intercalation in ZnAl-LDH.

Antibacterial Tests

The inhibition zones are shown in Figure 4 and the diameters of their sizes are summarized in Figure 5 and Table 3. The experiments were done three times to confirm the obtained results. The results revealed that ZnAl-Cl material sample has excellent antibacterial activity against the mentioned bacteria; presumably for the fact that ZnAl LDH presents a positive charge. This might be as a result of peptide polyglycogene existing in the cell border of gram positive bacteria and operating with plenty of pores that allowed stronger molecules to penetrate into the cell easily [START_REF] Mohamed | Quaternized N-substituted carboxymethyl chitosan derivatives as antimicrobial agents[END_REF]. Another elucidation is zinc ion, it has a magnificent effect on both bacteria [START_REF] Sugarman | Zinc and infection[END_REF] indicating that metallic ion-exchanged LDH diffused in water attracted bacteria by electrostatic forces, which explain the perfect antibacterial activities [START_REF] Dizman | Antibacterial fluoromicas: A novel delivery medium[END_REF][START_REF] Parolo | Antimicrobial properties of tetracycline and minocycline-montmorillonites[END_REF].

Conclusion

Zn-Al LDH an Zn-Al-DDPA synthesized in the laboratory and characterized by XRD, FTIR, BET, and the elementary analysis showed high antibacterial activity against all the tested microorganisms such as E.coli (ATCC 25922), Streptococcus (ATCC 25922), Bacillus (ATCC 25922). The antibacterial activity was evaluated with respect to the inhibition zone size in mm, therefore, this hybrid material exhibited very good antibacterial potency, and such a result gives evidence of the feasibility of the samples as "active antibacterial" materials.

Figure 1 :

 1 Figure 1: diamino dodecylphosphoni acid Molecule.

Figure 2 :

 2 Figure 2: XRD patterns of Zn/Al-LDH and Zn/Al-DDPA.

Figure 3 :

 3 Figure 3: FTIR spectra of ZnAl-LDH and ZnAl-DDPA.

Table 4 :Figure 5 :

 45 Figure 5: Histogram representing the zone of inhibition of bacterial.

Table 1 : Chemical composition of ZnAl-LDH and ZnAl-DDPA.

 1

	Sample composition Zn (wt%)	Al (wt %) Cl (wt%)	P (wt%)	C (wt%)	Zn 2+ /Al 3+ molar ratio
	ZnAl-LDH	44.16	9.08	11.98	11.98		2.0
	ZnAl-DDPA	15.48	3.29	-	-	6.01	1.9
		BETsurface area(m2g-1)	Pore volume(cm3g-1)	Average pore size(nm)
	ZnAl-LDH	62.4854			0.2908		18.6157
	ZnAl-DDPA	10.3297		0.009791		3.7912

Table 2 : Pore properties and specification surface area of ZnAl-HDL and ZnAl-DDPA. Bacterial strains Gram-negative Gram-positive

 2

		E.Coli	Bacillus ATCC 25922	Sterptocoque
		ATCC 25922		ATCC25922
	ZnAl-Cl	40mm+0,5	20mm+0,7	25mm+0,1
	ZnAl-DDPA	43mm+0,05	25mm+0,08	32mm+0,04

Acknowledgements

This work was supported by Dr Moulay Tahar University, Saida, Algeria and "PunchOrga" Network (Pole Universitaire Normand de Chimie Organique), the "Ministère de laRecherche et des Nouvelles Technologies," CNRS (Centre National de laRecherche Scientifique).