Ekaterina Glebova
email: katrina.glebova@universite-paris-saclay.fr

Anna Gerke
email: agerke@audencia.com

Book chapter: The Transformational Role of Technology in Sports Events

Keywords: sport event, technology, transformation, security, fan engagement, broadcasting, connected stadium, sustainable sport

The rapid uptake of various technological products and services transforms many fields of human life, including the sports industry. In the current chapter we discuss the process of technological transformation in sports for different stakeholders, and the role of particular innovations in this ongoing phenomenon. It extends the literature on the intersection of sport management and technology, followed by vivid cutting-edge examples from the field. In greater detail, we explain how and why new technology innovations are disseminated and used, affecting sports training, performance, judging, and spectating. Consequently, it reshapes tools, and strategies for event and sport management, bringing, on one hand, uncertainty and ambiguity, but, on the other hand, new marketing and management opportunities for all stakeholders. However, to use these opportunities and to turn them into an advantage, sport management professionals have to profoundly understand the nature, trajectory, and impact of the current technology-centered transformation in the industry. In this chapter we define and describe all these constructs, providing a deep explanation of the transformational role of technology in sports events and the sports ecosystem in general. It is addressed to a wide range of readers: students, scholars, sports, and technology professionals. Complementary, we define the perspective directions and agenda for future research.

Introduction

The use of technological applications is now widespread across the world by all sports fans, teams, brands, associations, coaches, and athletes and the adoption of these tools to gain a 'competitive advantage' is an increasingly important feature of sports (Giblin et al., 2016). Nowadays technologies are ready to offer to all stakeholders new ways to manage and experience sports events. Many digital, technical, and social aspects of today's sports marketing environment have served as a contextual frame for this chapter on the emergence of new mobile applications (apps), the Internet of things, (IoT), Immersive technologies (XR), 5G, hardware and software, which demonstrates the emergence of new forms of sports marketing, management and consumption.

The current chapter focuses on the drastic role of technology in modern sports events, explaining in detail different aspects of impact, contributing to understanding how technologies change and will change sports events.

As a result of this chapter, the readers will:

• Understand the nature, trajectory, and roles of technologies in sport events • Be aware of developing issues and trends that affect the present and future technologies deployment in sports entertainment • Appreciate factors that contribute to transforming and enhancing sports performance, analytics, and spectating • Recognize the importance of technologies' wide dissemination and their effect on event management • Recognize the need for research, data analysis, and accountability when planning, deploying, and managing technologies in spectators' experiences (SSCX) • Understand how sports events are transforming through technology • Comprehend the importance of emerging technologies in terms of nowadays sports • Foresee the future research and development paths and directions

Theoretical background and key constructs

Recent academic research focuses mostly on the intersection of technologies and sports performance and exercising, but the understanding of the role of technologies in sports spectacle and event management attracts attention as well [START_REF] Glebova | Sport et technologies numériques: vers de nouvelles expériences spectateur (Sport and digital technologies: towards new spectator experiences)[END_REF]Glebova & Desbordes, 2021b).

There is a large array of technological innovations and tools available to fans, brands, coaches, and sports performers. This paired with the increased desire to collect and process information rapidly and at minimum cost to the user leads towards the growth of technologically highly sophisticated products. Hence, fundamental transformations happen in sports ecosystems, more specifically in the interactions of the provider with the user.

The role of technologies in the sports ecosystem is constantly growing, including for events at all levels and scales. Glebova and Desbordes (2021b) see technology as the main driver of improving the customer experiences of sports spectators. Moreover, technologies change the way how sports events are organized and managed [START_REF] Rai | Information Technology in Sports Management-An Overview[END_REF]. At the same time, with the influx of technologies being adapted to the sport, there is a critical need in addressing the issues arising from the integration of these innovations [START_REF] Mallen | Introduction to emerging technologies and their implications in sport management: Implications for Sport Management[END_REF].

Technology was defined as the most dramatic change and a "Game Changer" in the service field [START_REF] Ostrom | Service Research Priorities in a Rapidly Changing Context[END_REF]. Merriam Webster Dictionary simply defines technology as 1a: the practical application of knowledge especially in a particular problem b: a capability is given by the practical application of knowledge 2: a manner of accomplishing a task, especially using technical processes, methods, or knowledge 3: the specialized aspects of a particular field of endeavor According to Rotolo (2015), all emerging technologies share five key attributes: radical novelty, relatively fast growth, coherence, prominent impact, uncertainty, and ambiguity. Thus, all technologies we discuss in the current chapter may be considered emerging.

The theoretical construct "technology" is unclear in literature and sometimes it is used misleadingly. Often "technology" conveys "technology-based products/services". For this chapter, it seems to be important, because technology is a manner of accomplishing a task, but a technological product/service is a product/service based on this technology. For example, AI is a technology, but an AI-based service robot is a technological product, the Internet is a technology, but a mobile phone connected to the internet is a technology-based product (Glebova & Desbordes, 2021a).

In order to define the nature, courses, and impact of technologies in sports, Glebova and Desbordes (2021a) have developed a typology of technology innovations in sports, based on the three aspects: context, consumer, innovation nature. Furthermore, it explains the circle (evolution continuum) of the interrelation of sport technology innovation and cultural aspects of the sport, embracing the key elements: cultural perspectives of sports business, ecosystem, innovation, and sport technology innovations.

All sports events are different in many terms. [START_REF] Gammon | Sports events: typology, people and place[END_REF] distinguishes the following types of sports events: (1) special, (2) mega, (3) hallmark, (4) sports heritage, (5) parades and festivals, (6) small scale/community. Any kind of sports event involves a number of stakeholders (a person or entity with an interest or concern related to a particular event or business process; Glebova & Desbordes, 2021b). In a sporting event, typically, there are key stakeholders (Table ): spectators/ fans, athletes/ teams, sports organizations, sponsors, sports brands, employees/ volunteers, among others. The development and roles of stakeholder relationships through three phases in the development and delivery: pre-event, event time, and post-event [START_REF] Kristiansen | Stakeholder Management of Temporary Sport Event Organizations[END_REF]. Each stakeholder has its own role(s), often overlapping. For example, there are a few stakeholders, who can be defined as a consumer in the framework of a sporting event. Notably, Shank (2005) stated that the sports industry seeks to satisfy the needs of three distinct types of consumers: spectators, participants, and sponsors.

Technologies in sports events

Different technologies play different roles in sporting events for different stakeholders. Subsequently, to define a role of a particular technology in modern sport event management, the function of technology and its impact from the stakeholders' perspective matters (Friedman & Miles, 2002). Particularly, the transformation can be seen in terms of security, fan engagement, efficiency and effectiveness of resources use and allocation, sustainability, accessibility and inclusion, and sport video broadcasting (Figure 1; Figure 3).

Security

It is difficult to underestimate the importance of security and safety in sporting events at all levels. Security includes a complicated, specialized, long-term preparation process and planning, involving all stakeholders directly or indirectly. Nowadays, with digital technologies, many security tasks become simplified and automatized. However, it also raises new issues: ethics and cyber security.

The majority of the modern security technologies are based on data: camera surveillance, identification, profiling, and analytics involving pieces of personal data. On one hand, it can be seen as a powerful tool for security management and control, but on the other hand, it is not in compliance with legislation in terms of data collection and proceeding [START_REF] David | New Digital Technologies: Privacy/Property, Globalization[END_REF][START_REF] Quach | Digital technologies: tensions in privacy and data[END_REF]. By way of illustration, in France, the president of the CNIL (fr: Commission nationale de l'informatique et des libertés1 ) has issued a warning to the sport society which was assessing the use of a system of facial recognition in order to automatically identify people subjected to commercial prohibition into the stadium (CNIL, 2021). This system aims to detect lost objects, recognize people subjected to commercial ban into the stadium, among other security purposes. The technology is based on biometric data processing, precisely physical or biological human characteristics (for example, DNA, footprints, hand contour). Sure enough, according to the General Data Protection Regulation (GDPR) and the Data Protection Act, any collection and management of human personal data are forbidden. Thus, the implementation of facial recognition and other personal identity technologies by sports associations are illegal without special legislative disposals or a regulation.

Fan engagement

Fan engagement is the process of delivering an end-to-end customer experience (throughout the duration of the customer-product interaction, re-entering at various touchpoints) to a sport spectating audiences at all stages of their customer journey (before, during, and after an event). Beyond sport events, fan engagement involves all types of fans' networking and communications. It is often confused or mixed up with 'involvement', which implies 'doing to', whilst 'engagement' means 'doing with' [START_REF] Harrigan | Customer engagement and the relationship between involvement, engagement, self-brand connection and brand usage intent[END_REF].

By leveraging the new technological innovations in data analytics, sport managers can enhance the emotional experience and take fan engagement to exciting new levels. Today, it seems difficult to make an exhaustive list to outline the full vast multiplicity of various technologies integrated with the sports industry: big Data, Immersive technologies, the Internet of things (IoT), Blockchain, Social Media, Mobile applications (apps), Service robots, Digital assistants, Artificial intelligence (AI), among others. All these technologies (and technology-based products and services) are often linked to each other, overlapping in terms of nature, deployment, and usage. That's why in today's sports marketing context technologies should be considered holistically, inseparable one from another. The proliferation and infusion of rapidly advancing technologies has attracted much attention from both research and industry, and fundamentally changed the way customers and the service field communicate and interact in the following points:

• Interactive and engaging ways to deliver experiences • Delivering "smooth" experiences becomes easier for sport management professionals • Easily accessible information, anytime from anywhere • Improving the quality of content • Personalization

• Transformation of the social aspect of fandom in terms of an opportunity to virtually reach people at a physical distance • Sports spectating becomes more and more inclusive, embracing female fans, kids, disabled people

Principally, the advancements in data collection and analysis lead to a personalization of experiences.

Today we observe an unprecedented growth of immersive technologies (common abbreviation: XR for eXtended Reality) development, particularly, virtual reality (VR), augmented reality (AR), mixed reality (MR), and immersive environments (IE). Immersive can be seen as the main tool or as a supplementary channel to enhance SSCX and deliver a piece of information to an end-user. For example, the Minnesota Vikings museum invites sports fans to experience virtual competitions with professional players through VR. Indeed, it illustrates a trend of gamification of fan experiences as a part of the engagement strategy.

In the framework of IoT and internet coverage technology helps fans to buy tickets, find their seats, check toilets' availability, find parking, and order food, making X more comfortable. However, the term "Connected Stadium" is not embracing technology or infrastructure only. For example, Postmates is the exclusive on-demand food delivery partner of the Yankees Stadium. Implementation of this concept means that food and beverage choice is no longer limited by an in-stadium offer. A fan may choose and order any restaurant they want and order delivery right to the stadium. Obviously, Food and Beverage (F&B) is an essential part of the basic in-stadium experience [START_REF] Parry | Who ate all the pies? The importance of food in the Australian sporting experience[END_REF]. And Posmates illustrates the smart and simple solution to a complicated problem. By the way, as a part of technological transformation, the evolution of additional in-stadium services opens many questions. For example, how it may impact stadium attendance, in-stadium sales, customer satisfaction? Nowadays, this question does not have any univocal single answer, it always depends on a particular case.

The majority of technological advances in terms of user experiences (UX) are integrated through mobile apps, consolidating all user data. Smartphones have taken over the traditional laptops and tablets, and are becoming more and more versatile in terms of usage [START_REF] Glebova | Sport et technologies numériques: vers de nouvelles expériences spectateur (Sport and digital technologies: towards new spectator experiences)[END_REF][START_REF] Zandt | Majority of Internet Traffic Created on the Go[END_REF]. Accordingly, the mobile app industry is evolving and uptake all possible fields of life and activity, for example, reservations, gaming, gambling, paying bills, ordering tickets, communications, broadcastings, search, and leisure time. Consumers' use of mobile applications (apps) poses multiple challenges for research in consumer behavior (e.g., ….) and companies have seen them as a new way to communicate with customers. The sports industry and event management have been benefiting from this development. Nowadays, athletes, sports teams, and organizations employ App Marketing (i.e., development and management of marketing campaigns that communicate with fans at every stage of their customer journey; [START_REF] Lee | Enhancing customers' continued mobile app use in the service industry[END_REF][START_REF] Guo | Enhancing mobile app user understanding and marketing with heterogeneous crowdsourced data: a review[END_REF][START_REF] Glebova | Sport et technologies numériques: vers de nouvelles expériences spectateur (Sport and digital technologies: towards new spectator experiences)[END_REF]) which is showing great marketing results [START_REF] Sung | The effects of augmented reality mobile app advertising: Viral marketing via shared social experience[END_REF].

In terms of sports events, a mobile application is a multi-purpose technology-based product. It is supposed to connect a customer with absolutely all aspects of the event. For example, in terms of safety, through a mobile application, stadium visitors can anonymously report safety concerns, suspicious activity, and unattended packages directly to the stadium's security officials. Thus, it is a way to seek medical assistance, find informational support in critical moments, check parking and toilet availabitlity in real time. Fans are also able to interact with security officials through two-way communications and send photos, videos, and audio to provide specific details. The mobile application essentially allows fans in the venue to be the eyes and ears for security.

An application can also be used to enter the stadium with mobile tickets, order in-seat F&B delivery, order merchandise express pickup and watch instant replays, follow analytics, and do shopping (e.g. fans memorabilia). As such, not only is the mobile application helping to improve the venue security, but it also helps to improve the fan experience.

Events, brands, organizations, venues are developing their mobile app(s) because it's the "place" for all services and customer interactions. Access to all information and services is structured in a single system, easily accessible for consumers. For example, a sport event may include its mobile stores as an online-commerce option in an app. It would help offer an inclusive mobile experience for fans, allowing users to buy club memorabilia through their mobile devices. From all these points of view, mobile apps are versatile powerful marketing tools for sports managers and a useful information source for fans as well.

Social media and communication platforms expand fan experience in the direction of social interactions and information exchange. It is a root of numerous forms of nowadays social media influence at an intersection with sport events: fans' online communities, formation of public opinion, user-generated content, influencer marketing, and CRM (customer relationship management), among others.

Customer relationship management (CRM) can be defined as the technology itself for establishing and maintaining relationships with current and potential customers. Undoubtedly, it involves plenty of technological tools, for example, digital communication, analytics software, algorithms, and communication techniques. Notably, it allows for building customer engagement and intimacy with behavior-based CRM with a featured mobile app front end [START_REF] Jaysinghe | Customer Engagement, CRM and Intimacy: A Study of Mobile App Effectiveness[END_REF]. Furthermore, it is not only allowing for the building of data-driven marketing strategies and conducts enhanced interactions with customers but also puts forward efficiency and effectiveness.

Efficiency and effectiveness of resources use and allocation

Modern technologies allow managing events effectively and efficiently. Artificial Intelligence (AI) tools in sports are continuously emerging all over the industry, covering operations management, financial aspects, advanced performance analysis, and fan experience. Among these tools, there are sensors, wearables, and computer vision-powered cameras to collect data, whereas, natural language processing devices can leverage speech and text recognition to gather insights regarding the audiences. This volume of work is difficult, even impossible, to be done by a human employee. Thus, all these technological tools can be used for the optimization of costs and resources in sport event management to create forecast models, help stakeholders through their decision-making, and automatize operations and processes related to broadcasting and fan experience. However, replacing a human, AI raises ethical issues like, for example, unemployment.

Human work can be automatized for many functions, being replaced by AI, robots, and machines.

Representing AI tools, Virtual assistant referees (VAR) have been used in football for years to provide slow-motion highlights to human umpires, but with the disadvantage of slowing down the game. The new algorithms are addressing this problem by improving VAR to be faster and more accurate in detecting game violations. Content creation can be the next example, since using machine learning and deep learning algorithms, broadcasters can automate numerous content creation functions, including camera position and zoom in on key field actions in real-time.

Sustainability

Generally speaking, sustainable sport events seek to reduce the sport's ecological footprint on the environment. How can sporting events be sustainable? Sustainable events are supposed to address (entirely or partially) 17 of the United Nations Sustainable Development Goals (SDG), thus, they may embrace many overlapping components, for example, carbon awareness, low waste policy, innovative energy solutions. All the sustainable solutions for sport events are primarily based on technology. Event organizers, hosts, consumers, and suppliers share responsibility for implementing and communicating sustainable practices between all stakeholders and technological advancements help in this mission. For example, the Helsinki International Horse Show (the largest indoor sporting event in Finland) has taken part in zero-waste measures, since in 2021 it was fully maintained by electricity generated from horse manure 2 .

The environmental ambitions of the Paris 2024 Olympic Games convey the commitment of the International Olympic Committee (IOC) to become a climate-positive organization by 2024 and further have solitary climate-positive Olympic Games in the future, from 2030 onwards (Figure 2).

Accessibility and inclusion

With constant improvements in digital entertainment systems and internet connectivity occurring all the time, sport fans can build themselves a spectating experience that fits their preferred specifications without any limitations in place, or services. Sport is available to be watched in full digital clarity anytime from anywhere, bringing all sport fans to the "Global Stadium", embracing social media and OTT platforms ("Over The Top", any streaming service that delivers content over the internet). It makes the event accessible for a wide range of people, regardless of their physical location, age, social and financial status, health condition, and disabilities: everyone and everywhere can watch sports events by joining the stream/recording watching provided by modern technologies.

Also, connectivity gives more opportunities to disabled people to enjoy visiting a stadium: digital navigation, parking, and toilet accessibility real-time check, food delivery to a seat. Particularly, for inclusive and universal mobility, mobile applications like Evelity 3 guide people with disabilities through complex places of everyday life, including sport stadia, providing a step-by-step guidance like a pedestrian navigation, both indoors and outdoors. Evelity proposes routes and indications and userfriendly interfaces, customized for each profile (disabled or not).

Sport video broadcasting

Finding new and innovative ways to enhance the experience for absolutely all fans has taken on increased significance, hence, the improvement of spectating is one of the key roles of technology in sporting events. Indeed, technological applications are capable to improve broadcasting for all the stakeholders, including the production team. Notably, AI-powered automatical cameras allow youth sports to employ a high-quality broadcast without an expensive on-site production team. The computer vision is used to identify elements of the game (athlete, equipment, gate, etc), then, autonomously follow the performance, capturing the key moments. Moreover, the customized graphics and data analytics can also be automatically applied to the footage for spectators engagement. It illustrates how AI enables streaming and recording events from an automated camera system without any production team on the field.

Emerging XR technology, for example, metaverse 4 promises an opportunity for fully immersive virtual experiences. In terms of sport events, it can be a feeling and experience of a physical presence in a stadium without being there. It opens absolutely new perspectives on sport spectating and it will definitely reshape and shift the sports economy. In this regard, nowadays XR seems to be one of the most interesting research paths and themes for further development at the intersection with the sports industry and event management.

Conclusion

As we described in this chapter, technologies can be seen as a key, tool, and catalyst for transforming sport events. Technologies of different types play a crucial role for all the stakeholders, in terms of security, fan engagement, efficiency and effectiveness of resources use and allocation, sustainability, accessibility and inclusion, sport video broadcasting (Figure 3).

Figure

  Figure 1: Technologies in sport events in the contemporary context

Figure 2 :

 2 Figure 2: Sustainability becomes central to the Olympic Movement's vision of "building a better world through sport" (Olympic Games 2024, official website, infographic)

Figure 3 :

 3 Figure 3: Technological transformation of sport events

  evelity.com/en/ [last access: 01/04/2022] 4 https://about.facebook.com/meta/ [last access: 01/04/2022]

		Engage ment	Security
		Sport
	Broad casting	Events Tech Transfor	Efficiency
		mation
	Inclusion		Sustain ability

The CNIL is an independent French administrative regulatory body whose mission is to ensure that data privacy law is applied to the collection, storage, and use of personal data: https://www.cnil.fr/en/cnils-missions


Dzmitry Melnikau

Alexander A Govyadinov

Ana Sánchez-Iglesias

Marek Grzelczak

Igor R Nabiev

Luis M Liz-Marzán

Yury P Rakovich
email: yury.rakovich@ehu.eus

Ana Sánchez-Iglesia

Double Rabi Splitting in a Strongly Coupled System of Core-Shell Au@Ag Nanorods and J-Aggregates of Multiple Fluorophores

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multimode hybridization and energy transfer, which is of considerable interest in both fundamental and applied science. Here we demonstrate that three different components such as core-shell Au@Ag nanorods and J-aggregates of two different dyes, can be integrated into a single hybrid structure, which leads to strong collective exciton-plasmon coupling and double-mode Rabi splitting totaling 338 meV. We demonstrate strong coupling in these multicomponent plexitonic nanostructures by means of magnetic circular dichroism spectroscopy, and demonstrate strong magneto-optical activity for the three hybridized states resulting from this coupling. The J-aggregates of two different non-magnetic dyes interact with metal nanoparticles effectively, achieving magnetic properties due to the hybridization of electronic excitations in the three-component system.

TOC GRAPHICS

KEYWORDS Strong coupling, double Rabi splitting, J-aggregates, plexciton, magneto-optical activity, magnetic circular dichroism.

The interaction of organic and inorganic materials in a strong coupling regime significantly changes the characteristics of the individual components, yielding a hybrid system with new physical and chemical properties. It has been recently demonstrated that strong coupling can affect the rate of chemical reactions [START_REF] Hutchison | Modifying Chemical Landscapes by Coupling to Vacuum Fields[END_REF] , pathways of energy-and electron-transfer [START_REF] Coles | Polariton-mediated energy transfer between organic dyes in a strongly coupled optical microcavity[END_REF][START_REF] Wiederrecht | Control of Molecular Energy Redistribution Pathways via Surface Plasmon Gating[END_REF] , fluorescence [START_REF] Melnikau | Splitting in Photoluminescence Spectra of Hybrid Systems of Gold Nanorods and J-Aggregates[END_REF][START_REF] Dong | Generation of molecular hot electroluminescence by resonant nanocavity plasmons[END_REF] , conductivity [START_REF] Orgiu | Conductivity in organic semiconductors hybridized with the vacuum field[END_REF] and magnetic properties [START_REF] Melnikau | Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures[END_REF] of integrated materials.

The strong coupling regime is achieved when the rate of coherent energy exchange between excitons and plasmons exceeds the dissipation rate in the plexcitonic system [START_REF] Wiederrecht | Coherent Coupling of Molecular Excitons to Electronic Polarizations of Noble Metal Nanoparticles[END_REF] . This leads to the formation of new hybrid plexciton states (which causes spectral Rabbi splitting) with remarkable mixed properties in the assembled materials, thereby providing new opportunities for various applications in the fields of information processing [START_REF] Kurizki | Quantum technologies with hybrid systems[END_REF][START_REF] Reithmaier | Strong coupling in a single quantum dot-semiconductor microcavity system[END_REF][START_REF] Hennessy | Quantum nature of a strongly coupled single quantum dot-cavity system[END_REF] , sensing [START_REF] Melnikau | Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures[END_REF] and being at the core of plasmonic switches based on the strong coupling effect [START_REF] Ming | Resonance-Coupling-Based Plasmonic Switches[END_REF] .

Apart from "classical" double-component strongly coupled systems, another direction with significant untapped potential in the field of light-matter interactions is the study of strongly coupled multicomponent systems. The emergence of multiple Rabi splitting in such systems is of considerable interest and relevance for both fundamental and applied science, providing remarkable opportunities for studies of multimode hybridization and energy transfer [START_REF] Coles | Polariton-mediated energy transfer between organic dyes in a strongly coupled optical microcavity[END_REF][START_REF] Hakala | Vacuum Rabi Splitting and Strong-Coupling Dynamics for Surface-Plasmon Polaritons and Rhodamine 6G Molecules[END_REF][START_REF] Wang | Multimode Coherent Hybrid States: Ultrafast Investigation of Double Rabi Splitting between Surface Plasmons and Sulforhodamine 101 Dyes[END_REF][START_REF] George | Multiple Rabi Splittings under Ultrastrong Vibrational Coupling[END_REF][START_REF] Melnikau | Strong plasmon-exciton coupling in a hybrid system of gold nanostars and J-aggregates[END_REF] . Moreover, multimode strong coupling can open the way to multipartite entanglement and the implementation of quantum computing devices using multi-quasiparticle boson systems [START_REF] Hensen | Strong Coupling and Entanglement of Quantum Emitters Embedded in a Nanoantenna-Enhanced Plasmonic Cavity[END_REF][START_REF] Hartmann | Quantum simulation with interacting photons[END_REF] .

The development of strongly coupled multicomponent systems, namely two Jaggregated cyanine dyes incorporated in a microcavity, have led to the discovery of an efficient and ultrafast pathway for the energy-transfer between two exciton states 2 . Multiple spectral splittings for molecular vibrations coupled with a set of infrared cavity modes have also been reported [START_REF] George | Multiple Rabi Splittings under Ultrastrong Vibrational Coupling[END_REF] . Despite the fact that plasmon nanostructures (i.e. nanoresonators) are considered to be an alternative to microcavities for achieving a strong coupling regime [START_REF] Dovzhenko | Light-matter interaction in the strong coupling regime: configurations, conditions, and applications[END_REF] , so far there are no convincing reports on multiple Rabi splittings in coupled exciton-plasmon systems. In the only work we have found on this topic, double Rabi splitting was observed in the extinction spectra of a complex system comprising gold nanostars and J-aggregates of two dyes [START_REF] Melnikau | Strong plasmon-exciton coupling in a hybrid system of gold nanostars and J-aggregates[END_REF] . However, the strong interaction of the fluorophores with plasmonic nanostructures was not convincingly demonstrated.

Also we would like to note that recently double Rabi splitting was observed in dark-field scattering spectra using a plasmonic nanostructure interacting with two types of excitons (charged and neutral) in WS 2 with decreasing temperature [START_REF] Cuadra | Observation of Tunable Charged Exciton Polaritons in Hybrid Monolayer WS2-Plasmonic Nanoantenna System[END_REF] .

Here we unambiguously show that strong collective coupling can be reached in a system made of Au@Ag nanorods (NRs) and J-aggregates of two different dyes, which form a single nanosystem with unique multiple spectral features. We demonstrate magnetooptical activity for three hybridized plexciton states resulting from strong excitonplasmon coupling in multilayer nanostructures, in which the plasmonic component induces magnetic properties in non-magnetic organic fluorophores. Our findings are of significance for the development of new sensing systems based on magneto-optical activity, while significantly expanding the portfolio of materials that can be used for information storage and processing.

The extinction spectra of J-aggregates of 5,5′,6,6′-Tetrachloro-1,1′,3,3′-

tetraethyl-imidacarbocyanine iodide (TCI) and 2-[3-[1,1-dimethyl-3-(4-sulfobutyl)- 1,3-dihydro-benzo[e]indol-2-ylidene]-propenyl]-1,1-dimethyl-3-(4-sulfobutyl)-1H- benzo[e]
indolium hydroxide (DBI) dyes show narrow peaks (so called J-bands) red-shifted with respect to the respective monomer peaks (Figure 1a). Formation of J-bands and associated spectral shift upon aggregation of monomers is caused by the delocalization and migration of the exciton energy over a large number of aggregated dye molecules [START_REF] Kirstein | J-aggregates of amphiphilic cyanine dyes: Self-organization of artificial light harvesting complexes[END_REF] . The absorption maxima of J-bands are observed at 587 nm and 637 nm, with a full-width at half-maximum of 24.4 and 20 nm for TCI and DBI dyes, respectively. The synthesized Au@Ag NRs have rather wide plasmon resonance bands (200-300 eV) corresponding to the longitudinal modes, which are located in the spectral region of J-bands of TCI and DBI dyes (Figure 1a). We would like to note, that the width of plasmon peaks observed in our case in the spectra of ensembles of nanorods is dominated by the inhomogeneous broadening due to the dispersion of the of nanorods. As reported in previous studies, typical linewidths for single nanorods with the aspect ratios close to that of our samples were found to be, for example, 23-83 [START_REF] Novo | Contributions from radiation damping and surface scattering to the linewidth of the longitudinal plasmon band of gold nanorods: a single particle study[END_REF] , 75 [START_REF] Muskens | Quantitative Absorption Spectroscopy of a Single Gold Nanorod[END_REF] and 68 meV [START_REF] Heylman | Optical microresonators as single-particle absorption spectrometers[END_REF] .

In contrast to our previous work [START_REF] Melnikau | Splitting in Photoluminescence Spectra of Hybrid Systems of Gold Nanorods and J-Aggregates[END_REF] , in the present experiments we control the spectral position of the longitudinal surface plasmon resonance in the samples, not by changing the NR length but by varying the thickness of the Ag shell deposited on the Au NR core. Increasing the thickness of the Ag layer, which is known to preferentially grow on the sides of the Au NRs [START_REF] Gómez-Graña | Au@Ag Nanoparticles: Halides Stabilize {100} Facets[END_REF] , the aspect ratio (AR, the ratio of lengthto-width of NR) was varied from 3 to 2.5 (Figure 1a). Such an AR modification leads in turn to a shift of the longitudinal LSPR, from 655 nm to 610 nm (Figure 1a). Thus, an ideal overlap of the localized surface plasmon resonance (LSPR) band with the spectral position of the J-bands of both dyes can be ensured, providing the best conditions for a strong exciton-plasmon interaction in the developed nanostructures.

The double Rabi splitting in the extinction spectra of the hybrid structures was achieved as a result of the sequential assembly of TCI J-aggregates on Au@Ag NRs, followed by deposition of DBI J-aggregates. The interaction of two oppositely charged fluorophores stimulated the formation of a hybrid system comprising Au@Ag NRs coated with two layers of different J-aggregate dyes. It is also important to note that any attempt to create a separate hybrid system of bare Au@Ag NR and J-aggregates of DBI fluorophore, possessing strong coupling properties, was not successful. This is likely related to the efficient interaction of DBI dye with free (non-bound to NR surface) surfactant (benzyldimethylhexadecylammonium chloride, BDAC), which seems to be only weakly bound to the surface of the plasmon particle, thereby preventing efficient plasmon-exciton coupling. Interaction of DBI dye with BDAC was assumed on the basis that the positively charged polyelectrolytes, i.e. BDAC, hexadecyltrimethylammonium bromide (CTAB), poly(diallyldimethylammonium) chloride (PDDA) or polyethyleneimine (PEI), can trigger the formation of DBI dye aggregates.

In the extinction spectra of TCI/Au@Ag nanostructures, strong coupling effects manifest themselves as a pronounced dip in the region of the J-band (590-595 nm) with two plexciton peaks, associated to so-called upper (URs) and lower (LRs) resonances (indicated by arrows in Figure 2a). With an increase in the AR, a shift of both resonances is observed: the UR approaches the spectral position of the J-band, while the LR moves away from the absorption band of the excitons. As noted above, due to the specific chemical structure and polarity of DBI, J-aggregates of this dye do not form a bound complex with bare Au@Ag NRs, which would show spectral properties related to strong coupling. However, it turned out that the presence of an oppositely charged layer of TCI J-aggregates on the NRs surface triggers the formation of a multilayer hybrid system made of DBI J-aggregates with a NRs/TCI structure (see Methods for more information). We should emphasize that, as indicated in Methods, the simultaneous presence of two separate systems, namely one made of NRs covered only with J-aggregates of DBI, and another of NRs covered with only J-aggregates of TCI, is not possible.

Remarkably, the spectra of this new hybrid complex show double Rabi splitting for all NRs, regardless of their AR, with three plexciton peaks located at 560-567 nm, 614-626 nm and 660-688 nm, respectively, to which we further refer to as upper resonance (URd), medium resonance (MRd) and lower resonance (LRd). In between these plexciton peaks, two pronounced dips are also observed, with minima at 590-595 and 640-647 nm. These dips coincide with the spectral positions of the J-bands of TCI and DBI, but in both cases redshifted by several nanometers relative to the extinction maxima of J-aggregates. We attribute this effect to a Lamb shift caused by adsorption of J-aggregates on the NRs surface [START_REF] Melnikau | Splitting in Photoluminescence Spectra of Hybrid Systems of Gold Nanorods and J-Aggregates[END_REF] .

As shown in Figure 2b, the lineshapes in the spectra of both NRs/TCI and NRs/TCI/DBI structures for NRs with different ARs are properly described by the theoretical model (see details in the Supporting Information, SI), which takes into account the coating of gold NRs with two layers of J-aggregates of different dyes.

The dips observed in the spectra of the hybrid plasmon-exciton structure are due to the formation of two distinct hybridized states (plexcitons), which leads to Rabi splitting in optical spectra [START_REF] Melnikau | Splitting in Photoluminescence Spectra of Hybrid Systems of Gold Nanorods and J-Aggregates[END_REF][START_REF] Melnikau | Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures[END_REF] . To sum up the data on exciton-plasmon coupling in the system of Au@Ag NRs with different aspect ratios and TBI and DBI J-aggregates, we plotted the spectral position of the hybridized plexciton states as a function of the position of the plasmon peak in the spectra of bare NRs for the case of single (Figure 3a) and double Rabi splitting (Figure 3b).

Correlating the theoretical and experimental data obtained for the NRs/TCI hybrid structure (Figure 3a), we revealed an anti-crossing effect as a result of the strong coupling between the NRs plasmon and the exciton of J-aggregates, which leads to a considerably large Rabi splitting 175 meV. The value of was ℏΩ 𝑅 ≈ Ω 𝑅 evaluated as the difference between the UR and LR energies at zero detuning (intersection of dashed lines in Figure 3a) by fitting the theoretical model, adopted from Ref. [START_REF] Abe | Surface plasma resonance and magneto-optical enhancement in composites containing multicore-shell structured nanoparticles[END_REF] (solid lines in Fig. 3a,b) and described in SI, to the experimental data. Figure 3b also shows the theoretical results (solid lines, see SI for modeling details) for Ag@Au NRs with two J-aggregates fitted to the experimental data obtained for the hybrid plexiton states in the case of double Rabi splitting. Using this model to interpolate/extrapolate the experimental data (symbols in Figure 3b) to zero detuning allows for estimating the Rabi splitting values to be 175 ℏΩ 𝑅1 ≈ and 163 meV. These values of Rabi splitting for the Au@Ag/TCI/DBI ℏΩ 𝑅2 ≈ hybrid structures are comparable to the data reported for two different Jaggregated molecular dyes incorporated in a microcavity [START_REF] Coles | Polariton-mediated energy transfer between organic dyes in a strongly coupled optical microcavity[END_REF] . Moreover, in our system, where all three components are involved in the strong interaction in a concerted manner, the total value of 338 meV reflects the onset of collective extended energy splitting between the states of the lower and upper plexitons (Figure 3b,d).

Another striking result of this study is the detection of a strong magneto-optical (MO) activity of the collectively interacting three-component exciton-plasmon system. It has been shown that the metal nanoparticles themselves possess MO activity [START_REF] Pineider | Circular Magnetoplasmonic Modes in Gold Nanoparticles[END_REF] . It was intriguing to check whether all three components of the system show the MO response when interacting in the strong coupling regime. If so, this will be another proof that all components of the system are strongly coupled to each other, working in unison.

To get a deeper insight in this issue, the MO properties of Au@Ag NRs, integrated with the J-aggregates of two different dyes, were studied. In these experiments, magnetic circular dichroism (MCD) spectra (the difference between the absorbance of left-and right-hand polarized light, ΔA(λ), under an applied magnetic field) were recorded for all samples. The results are plotted in Figure 4. different aspect ratios (blue line), (ii) hybrid structure consisting of Au@Ag NRs and TCI J-aggregates (red line) and (iii) hybrid structures of Au@Ag/TCI/DBI (green line). The MCD spectra were obtained by applying magnetic fields B= 1T (solid lines) and B= -1T (dashed lines).

First, in our experiments a strong MO response was found for bare Au@Ag NRs with different ARs and for the hybrid structures of Au@Ag/TCI J-aggregates (Figure 3, blue and red curves, respectively), which is consistent with previous reports 7, [START_REF] Sepúlveda | Highly sensitive detection of biomolecules with the magneto-optic surface-plasmonresonance sensor[END_REF][START_REF] Pineider | Circular Magnetoplasmonic Modes in Gold Nanoparticles[END_REF][START_REF] Artemyev | Low-field magnetic circular dichroism in silver and gold colloidal nanoparticles of different sizes, shapes, and aggregation states[END_REF] . A change in the polarity of the magnetic field leads to a sign reversal for all MCD spectra. The magnetic properties of plasmonic nanoparticles can be described by a simple model that considers the circular motion of free electrons inside nanoparticles caused by the Lorentz force under the influence of an external magnetic field, with a cyclotron frequency proportional to the magnetic field [START_REF] Armelles | Magnetoplasmonics: Combining Magnetic and Plasmonic Functionalities[END_REF][START_REF] Fan | Magnet-controlled plasmons[END_REF] . As a result of this effect, in the case of bare Au@Ag NRs, the application of a magnetic field leads to different absorption for the left-and right-hand circular polarized light, resulting in a rather strong MCD signal. The MO response of the hybrid structures of Au@Ag/TCI J-aggregates arises from the strong plasmonexciton coupling, as described in detail in our previous work [START_REF] Melnikau | Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures[END_REF] .

For the hybrid NRs/TCI/DBI structures, the MCD spectral features correlate well with those in the absorption spectra of the system constituents and for each NRs AR show three distinct peaks in the spectral regions of UR d (around 550-565 nm), MR d (around 610-622 nm) and LR d (664-688 nm). The reversal of the MCD sign of all the peaks of the hybrid NRs/TCI/DBI structure in the MCD spectra observed for the opposite polarity of the magnetic field (Figure 3, dashed lines) clearly demonstrates the magnetic nature of these peaks. It is of paramount importance that the J-aggregates of both TCI and DBI dyes themselves do not exhibit any pronounced magnetic properties in region of the J-band (SI Figure S1).

Nonvanishing MCD signal near the TCI and DBI excitons is the ultimate verification of the strong coupling in the system and unambiguously indicates that the plexitons of two different J-aggregates acquire magnetooptical activity due to coupling to the plasmonic nanostructure. The MCD spectra, normalized at the extinction maximum for 𝐴 max NRs with AR 3, are presented in Figure S2 and show that MO (ΔA/A max ) for three plexciton states of the hybrid NRs/TCI/DBI structure have similar values and are comparable in magnitude to MO of bare NRs. This comparable strength of MO actively confirms our conclusion of the strong coupling regime of interaction.

In summary, we have shown that all components of a hybrid NR/J-aggregate system are involved in strong interactions in a concerted manner, so that strong coupling between a plasmon and two excitons of J-aggregates of different dyes in multi-layer nanostructures, can lead to double Rabi splitting, significantly expanding the region of energy splitting between the states of plexcitons. All presented experimental results, supported by theoretical modeling, convincingly demonstrate a remarkably strong interaction of J-aggregates of two dyes and the plasmon system in the developed structures.

Exciton-plasmon strong coupling in a complex system consisting of two layers of J-aggregates of different dyes on Au@Ag NRs surface, is confirmed not only by theoretical modeling, but also by the results of MO activity in the same hybrid structures, which is the ultimate verification of the strong coupling in the system for each type of excitons. The manifestation of pronounced magnetic properties for the three plexciton states indicates that the plexitons of J-aggregates of two non-magnetic dyes effectively acquire "magnetic" properties from the plasmonic nanostructure, as a result of interactions in the strong coupling regime. Since in such a system, all hybrid plexciton states exhibit magneto-optical activity, MO can be used to study the fundamental properties of hybrid organic/inorganic systems in the strong coupling regime, which may also have great implications for biosensing, which is intrinsically insensitive to the organic background and thus offers a significant advantage over conventional spectroscopy methods. The development of a multi-component system with extended Rabi splitting represents a new paradigm for various applications even beyond sensing and opens up ample opportunities for research of multimode hybridization and fast and effective energy transfer between two excitons strongly coupled to plasmonic nanostructures.

METHODS

Cyanine dye 5,5′,6,6′-Tetrachloro-1,1′,3,3′-tetraethyl-imidacarbocyanine iodide, tetrachloroauric acid (HAuCl 4 ), sodium borohydride (NaBH 4 ), CTAB, BDAC, silver nitrate (AgNO 3 ), hydrochloric acid (HCl) and ascorbic acid (AA) were purchased from Sigma-Aldrich. Fluorophore

2-[3-[1,1-dimethyl-3-(4-sulfobutyl)-1,3-dihydro- benzo[e]indol-2-ylidene]-propenyl]-1,1-dimethyl-3-(4-sulfobutyl)-1H- benzo[e]
indolium hydroxide, inner salt, sodium salt S 2165 was obtained from FEW Chemicals. Gold NRs were prepared using Ag-assisted seeded growth [START_REF] Liu | Mechanism of silver(I)-assisted growth of gold nanorods and bipyramids[END_REF] . Seeds were prepared by the reduction of HAuCl 4 (5 mL, 0.25 mM) with NaBH 4 (0.3 mL, 10 mM) in aqueous CTAB solution (100 mM). An aliquot of seed solution (0.12 mL) was added to a growth solution containing CTAB (50 mL, 100 mM), HAuCl 4 (0.5 mL, 50 mM), ascorbic acid (0.4 mL, 100 mM), AgNO 3 (0.6 mL, 10 mM) and HCl (0.95 mL, 1000 mM). The mixture was left undisturbed at 30 ºC for 2 h. The solution was centrifuged twice (8000 rpm, 30 min) and redispersed in BDAC (10 mM) to obtain a final concentration of gold equal to 0.25 mM. The maximum of LSPR band of initially obtained gold NRs was 860 nm.

Core-shell

Au@Ag NRs were synthesized using benzyldimethylhexadecylammonium chloride (BDAC) as the capping agent [START_REF] Gómez-Graña | Au@Ag Nanoparticles: Halides Stabilize {100} Facets[END_REF] .

The typical reaction involved the addition of different amounts of AgNO 3 (10 mM) and ascorbic acid (100 mM) to the solution of gold NRs (10 mL, 0.25 mM) at 60 ºC. Larger amounts of silver caused more pronounced LSPR blue shifts. Addition of 1.0 mL, 0.9 mL, or 0.8 mL of AgNO 3 (10 mM), while maintaining the molar ratio of Ascorbic Acid to Ag + equal to 4, enabled us to reach LSPR maxima at 609 nm, 618 nm, or 655 nm, respectively. The solutions were left for 3 hours at 60 ºC under magnetic stirring. Finally, the solutions were centrifuged twice (6000-9000 rpm, 40 min) and redispersed in BDAC (2 mL, 15 mM).

J-aggregates of the TCI dye were formed spontaneously upon dissolution of this dye in aqueous NaOH or NH 3 solution (pH=8) [START_REF] Melnikau | Strong plasmon-exciton coupling in a hybrid system of gold nanostars and J-aggregates[END_REF][START_REF] Melnikau | Strong plasmon-exciton coupling in a hybrid system of gold nanostars and J-aggregates[END_REF] , while the formation of Jaggregates of DBI dye required addition of a positively charged polyelectrolyte, such as PEI, PDDA, or BDAC.

Hybrid structures of Au@Ag NRs and J-aggregates of TCI dye were obtained by addition of 10 µL of a concentrated ethanol solution of dye to 1 mL of an aqueous solution of NRs in the presence of ammonia (pH=8), followed by gentle stirring for 20 minutes. To separate J-aggregates bound to NRs from monomer dye molecules and free J-aggregates, the solution was centrifuged at 3500 rpm for 5 minutes and redispersed in water. Despite the fact that the concentration of the stabilizing agent BDAC is significantly reduced after centrifugation, the layer of TCI J-aggregates on the surface of Au@Ag NRs protects them from aggregation, thus providing a stable colloidal dispersion.

To form the hybrid system of Au@Ag NRs and J-aggregates of two different fluorophores, we used the electrostatic interaction between cationic groups of TCI and anionic groups of DBI dyes. In this procedure 3 µL of a concentrated aqueous solution of DBI dye was added to the previously prepared solution of hybrid structures of Au@Ag NRs and TCI J-aggregates followed by gently stirring the solution for 5-10 minutes. In turn, the presence of hybrid structures of Au@Ag/TCI J-aggregates in solution triggers the formation of J-aggregates of DBI dye.

Optical extinction spectra were measured using a Cary 50 spectrometer (Agilent Technologies). Transmission electron microscopy (TEM) images of NRs were obtained using a transmission electron microscope FEG-TEM, JEOL JEM-2100F UHR. For MCD experiments, a Jasco J-815 spectropolarimeter equipped with a water cooled GMW 3470 electromagnet (providing a static magnetic field of up to 1 T) was used.

The total value of magnetic circular dichroism was calculated as ,

Δ𝐴 0 = 𝜃/ ( ln10 4 )
where is the measured ellipticity, is the sum of CD due to molecular 𝜃 Δ𝐴 0 symmetry and MCD induced by the magnetic field. In this case, the CD was measured as the signal at zero magnetic field ( ), which was then subtracted 𝐵 from , yielding the MCD ( -the difference in absorbance between the right Δ𝐴 0 Δ𝐴)

and the left hand polarized light induced by an external magnetic field [START_REF] Sutherland | Magnetic Circular-Dichroism of Biological Molecules[END_REF] . ∆𝐴 depends on the absorbent concentration and can be expressed as: [START_REF] Mason | A practical guide to magnetic circular dichroism spectroscopy[END_REF]

ASSOCIATED CONTENT

The following files are available free of charge: (PDF)

Calculation of the absorption and MCD spectra for a nanorods solution coupled with J-aggregates. Absorption and MCD spectra pure TCI J-aggregates pure DBI J-aggregates (green line). Experimental and theoretical extinction and MCD spectra of core-shell Au@Ag NRs, hybrid core-shell Au@Ag/J-aggregates TCI structure and hybrid structure of core-shell Au@Ag/TCI/DBI NRs.

Figure 1 .

 1 Figure 1. (a) Experimental extinction spectra of an aqueous dispersion of core-

Figure 2

 2 Figure2shows that, for NRs with all considered AR, the LRs in the spectra of

Figure 2 .

 2 Figure 2. Experimental (a) and theoretical (b) extinction spectra of aqueous

Figure

  Figure 3c gives a simple schematic representation of the energy states in the

Figure

  Figure 3d illustrates the formation of hybridized plexciton states caused by the

Figure 3 .

 3 Figure 3. (a) Positions of LR (blue circles) and UR (red circles) in the

Figure 4 .

 4 Figure 4. Experimental (a) and theoretical (b) spectra of (i) MCD of Au@Ag NRs with

  , ∆𝐴 = ∆𝜀 𝑀 𝑐𝑙 where is the optical path length through the sample, is the molar concentration, 𝑙 𝑐 and is the differential molar extinction. To correctly compare the MCD ∆𝜀 𝑀 response in samples of different concentrations, the MCD signals were normalized at the absorption maximum , according to , 𝐴 max ∆𝐴(𝜆)/(𝐴 max 𝐵) ∝ Δ𝜀 𝑀 where is the absorption maximum for the particular sample. Such a 𝐴 max normalization essentially yields the intrinsic MCD parameter . In this work, we Δ𝜀 𝑀 consider the extinction spectra measured by our spectrometer as absorption Page 25 of 38 ACS Paragon Plus Environment The Journal of Physical Chemistry Letters spectra due to the weak light scattering by the used samples. All experiments were performed in ambient atmosphere at room temperature.Theoretical calculations were performed using the tensorial model developed in Ref.26. According to it, the nanorods were represented as several concentric spheroidal shells with the dielectric properties corresponding to Ag, Au and Jaggregated dyes and the experimental aspect ratios. Self-consistent solution of Maxwell's equations in each shell returns the effective dielectric tensor for the solution of particles dispersed in the host medium from which the absorption and the MCD signals can be calculated (see full details in the Supporting Information).

Figure 1 .

 1 Figure 1. (a) Experimental extinction spectra of an aqueous dispersion of core-shell Au@Ag NRs of different aspect ratios (2.5 -3.0) and absorption spectra of J-aggregates of TCI and DBI fluorophores (inset: chemical structures of TCI and DBI fluorophores). (b) TEM images of core-shell Au@Ag NRs with average aspect ratios varying from 2.5 to 3; scale bars are 50 nm. 200x185mm (150 x 150 DPI)

Figure 2 .

 2 Figure 2. Experimental (a) and theoretical (b) extinction spectra of aqueous dispersions of bare core-shell Au@Ag NRs (blue), the hybrid system of J-aggregates of TCI and Au@Ag NRs (red) and the hybrid structure of J-aggregates of two fluorophores (TCI and DBI) and Au@Ag NRs, with different aspect ratios. Experimental (c) and theoretical (d) absorption spectra of J-aggregates of TCI (red) and DBI (green) dyes. 192x192mm (150 x 150 DPI)

Figure 3 .

 3 Figure 3. (a) Positions of LR (blue circles) and UR (red circles) in the experimental extinction spectra of the hybrid structure of Au@Ag NRs and TCI J-aggregates dye, as a function of the plasmon peak position in the spectra of bare NRs. (b) Positions of LRd (blue squares), MRd (green squares) and URd (red circles) in the experimental extinction spectra of the hybrid structure of Au@Ag NRs and J-aggregates of TCI and DBI dyes with double Rabi splitting, as a function of the plasmon peak position in the spectra of bare NRs. The blue, green and red solid curves show the theoretically calculated spectral positions of LRd, MRd and URd, respectively. The horizontal red and green dashed lines indicate the spectral position of the J-band of TCI and DBI, respectively. The diagonal blue dashed lines mark the position of the plasmon resonance. (c) Schematic representation of the strong coupling between the J-aggregates exciton (left) and the NRs plasmon (right), yielding two hybrid plexciton states. (d) Schematic representation of the strong coupling between the excitons of the J-aggregates of TCI and DBI (left) and the plasmon of Au@Ag NRs (right), yielding three hybridized plexciton states and double Rabi splitting. 261x174mm (150 x 150 DPI)

Figure 4 .

 4 Figure 4. Experimental (a) and theoretical (b) spectra of (i) MCD of Au@Ag NRs with different aspect ratios (blue line), (ii) hybrid structure consisting of Au@Ag NRs and TCI J-aggregates (red line) and (iii) hybrid structures of Au@Ag/TCI/DBI (green line). The MCD spectra were obtained by applying magnetic fields B= 1T (solid lines) and B= -1T (dashed lines).215x199mm (150 x 150 DPI)

ACKNOWLEDGMENT This work was supported by MINECO (Ministerio de Economiá y Competitividad), Spain, project Fis2016.80174-P (PLASMOQUANTA) and MAT2017-86659-R (MULTIMAGE). I.N. and Y.R. acknowledge support from the Ministry of Education and Science of the Russian Federation under grant no. 14.Y26.31.0011 and funding from the Basque Government (Grant No. IT1164-19). This work was coordinated under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency (Grant No. MDM-2017-0720).

AUTHOR INFORMATION

Corresponding Author *Yury.Rakovich@ehu.eus