The nanoscale manipulation of soft-matter, such as biological tissues, in its native environment has promising applications in medicine to correct for defects (eg. eye cataracts) or to destroy malignant regions (eg. cancerous tumours). To achieve this we need the ability to first image and then do precise ablation with sub-micron resolution with the same setup. For this purpose, we designed and built a multiphoton microscope and tested it on goldfish gills and bovine cells. We then studied light-matter interaction on a hard polymer (PMMA) because the nature of ablation of soft-matter in its native environment is complex and not well understood. Ablation and modification thresholds for successive laser shots were obtained. The ablation craters revealed 3D nanostructures and polarization dependent orientation. The interaction also induced localized porosity in PMMA that can be controlled.

The semiconductor Bloch equations (SBEs) are an insightful and well-established formalism for studying light-matter interactions in solids. When Coulomb interactions between electrons are omitted, the SBEs are simplified to a single particle model. The SBEs in this single electron approximation have been used extensively to model strong-field interactions in condensed matter. The SBEs in the length gauge provide an intuitive and numerically efficient model of high harmonic generation (HHG) in solids. In this approach, the SBEs involve Berry connections and transition dipole moments, which are gauge dependent structural quantities. This thesis studies the role of gauge symmetry in the SBEs, and how it can be exploited to facilitate efficient numerical analysis of HHG in solids. In the length gauge, the macroscopic current describing HHG can be decomposed into physically intuitive contributions. In particular, this leads to a contribution known as the "mixture" current, which has been overlooked by the HHG community until recently. We study the influence of this contribution using the analytic tight-binding model for gapped graphene. We derive an analytic gauge transformation that removes singular behaviour from the gapped graphene model, thus enabling efficient numerical integration of the SBEs. We also present an alternative approach for simulating dynamics in tight-binding models. Instead of simulating the SBEs in the usual basis of Bloch functions, we transform to the basis in which the tight-binding Hamiltonian is represented. The dipole matrix elements necessarily vanish in this basis, and the SBEs can be integrated using only the Hamiltonian matrix elements. We first generalize the SBEs to accomodate a non-diagonal Hamiltonian matrix, and we demonstrate this formalism numerically using two different tight-binding models. Finally, we derive a novel formulation of the SBEs which involve only gauge invariant matrix elements. Specifically, the Berry connections and transition dipole phases are replaced by a gauge invariant quantity known as the shift vector. This yields a fully gauge invariant description of HHG in solids, and the shift vector provides intuitive insight for HHG in systems with broken inversion symmetry. Further, the ability to describe HHG solely in terms of gauge invariant quantities raises new possibilities for tomographic reconstruction of crystal band structure, and this idea is discussed as a possible direction of future work.

<p>Collective behavior in many-body systems, where the dynamics of an individual element depend on the state of the entire ensemble, play an important role in both basic science research and applied technologies. Over the last twenty years, studies of such effects in cold atomic vapors have lead to breakthroughs in areas such as quantum information science and atomic and condensed matter physics. Nevertheless, in order to generate photon-mediated atom-atom coupling strengths that are large enough to produce collective behavior, these studies employ techniques that intrinsically limit their applicability. In this thesis, I describe a novel nonlinear optical process that enables me to overcome these limitations and realize a new regime of collective light-matter interaction.</p><p>My experiment involves an anisotropic cloud of cold rubidium atoms illuminated by a pair of counterpropagating optical (pump) fields propagating at an angle to the trap's long axis. When the pump beam intensities exceed a threshold value, a collective instability occurs in which new beams of light are generated spontaneously and counterpropagate along the trap's long axis. In order to understand the physical mechanism responsible for this behavior, I study first the system's nonlinear optical response when driven below the instability threshold. I find that the incident optical fields produce an optical lattice that causes the atoms to become spatially organized on the sub-wavelength length scale. This organization corresponds to the formation of an atomic density grating, which effectively couples the involved fields to one another and enables the transfer of energy between them. The loading of atoms into this grating is enhanced by my choice of field polarizations, which simultaneously results in cooling of the atoms from T~30 &mu;K to T~3 &mu;K via the Sisyphus effect. As a result, I observe a fifth-order nonlinear susceptibility &chi;^{(5)}=1.9x10^-12 (m/V)^4 that is 7 orders of magnitude larger than previously observed. In addition, because of the unique scaling of the resulting nonlinear response with material parameters, the magnitude of the nonlinearity can be large for small pump intensities (\ie, below the resonant electronic saturation intensity 1.6 mW/cm^2) while simultaneously suffering little linear absorption. I confirm my interpretation of the nonlinearity by developing a theoretical model that agrees quantitatively with my experimental observations with no free parameters.</p><p>The collective instability therefore corresponds to the situation where the cold vapor transitions spontaneously from a spatially-homogeneous state to an ordered one. This emergent organization leads to the simultaneous emission of new optical fields in a process that one can interpret either in terms of mirrorless parametric self-oscillation or superradiance. By mapping out the phase diagram for this transition, I find that the instability can occur for pump intensities as low as 1 mW/cm^2, which is approximately 50 times smaller than previous observations of similar phenomena. The intensity of the emitted light can be up to 20% of the pump beam intensity and depends superlinearly on the number of atoms, which is a clear signature of collective behavior. In addition, the generated light demonstrates temporal correlations between the counterpropagating modes of up to 0.987 and is nearly coherent over several hundred &mu;s. The most significant attributes of the light, though, are that it consists of multiple transverse spatial modes and persists in steady-state. This result represents the first observation of such dynamics, which have been shown theoretically to lead to a rich array of new phenomena and possible applications.</p> / Dissertation

The constantly increasing volume of information in modern society demands a better understanding of the physics and modeling of optical phenomena, and in particular, optical waveguides which are the central component of information systems. Two ways of advancing this physics are to push current technologies into new regimes of operation, and to study novel materials which offer superior properties for practical applications. This dissertation considers two problems, each addressing the above-mentioned demands. The first relates to the influence of high-order nonlinear effects on pulse collisions in existing high-speed communication systems. The second part is a study of pulse dynamics in a novel nanocomposite medium which offers great potential for both optical waveguide physics and applications. The nanocomposite consists of metallic nanoparticles embedded in a host medium. Under resonance conditions, the optical field excites plasmonic oscillations in the nanoparticles, which induce a strong nonlinear response.Analytical and computational tools are used to study these problems. In the first case, a double perturbation method, in which the small parameters are the reciprocal of the relative frequency of the colliding solitons and the coefficient of quintic nonlinearity, reveals that the leading order effects on collisions are radiation emission and phase shift of the colliding solitons. The analytical results are shown to agree with numerics. For the case of pulse dynamics in nanocomposite waveguides, the resonant interaction of the optical field and material excitation is studied in a slowly-varying envelope approximation, resulting in a system of partial differential equations. A family of solitary wave solutions representing the phenomenon of self-induced transparency are derived. Stability analysis reveals the solitary waves are conditionally stable, depending on the sign of the perturbation parameter. A characterization of two-pulse interaction indicates high sensitivity to relative phase, and collision dynamics vary from highly elastic to the extreme case where one wave is immediately destroyed by the collision, depositing its energy into a localized hotspot of material excitation. This last scenario represents a novel mechanism for &quot;stopping light&quot;.

I present in this thesis the design, implementation and measurement results of a narrowband quantum light source based on cavity-enhanced Parametric Down-Conversion (PDC). Spontaneous Parametric Down-Conversion (SPDC) is the workhorse in the field of optical quantum information and quantum computation, yet it is not suitable for applications where deterministic nonlinearities are required due to its low spectral brightness. By placing the nonlinear crystal inside a cavity, the spectrum of down-conversion is actively modified, such that all the non-resonant modes of down-conversion experience destructive interference, while the resonant mode sees constructive interference, resulting in great enhancement in spectral brightness. I design and construct such a cavity-enhanced down-conversion source with record high spectral brightness, making it possible to use cold atoms as the interaction medium to achieve large nonlinearity between photons. The frequency of the photons is tunable and their coherence time is measured to be on the order of 10 nanoseconds, matching the lifetime of the excited state of typical alkali atoms. I characterize extensively the output of the source by measuring the second-order correlation function, quantifying two-photon indistinguishability, performing quantum state tomography of entangled states, and showing different statistics of the source. The unprecedented long coherence time of the photon pairs has also made possible the encoding of quantum information in the time domain of the photons. I present a theoretical proposal of multi-dimensional quantum information with such long-coherence-time photons and analyze its performance with realistic parameter settings. I implement this proposal with the quantum light source I have built, and show for the first time that a qutrit can be encoded in the time domain of the single photons. I demonstrate the coherence is preserved for the qutrit state, thus ruling out any classical probabilistic explanation of the experimental data. Such an encoding scheme provides an easy access to multi-dimensional systems and can be used as a versatile platform for many quantum information and quantum computation tasks.

I present in this thesis the design, implementation and measurement results of a narrowband quantum light source based on cavity-enhanced Parametric Down-Conversion (PDC). Spontaneous Parametric Down-Conversion (SPDC) is the workhorse in the field of optical quantum information and quantum computation, yet it is not suitable for applications where deterministic nonlinearities are required due to its low spectral brightness. By placing the nonlinear crystal inside a cavity, the spectrum of down-conversion is actively modified, such that all the non-resonant modes of down-conversion experience destructive interference, while the resonant mode sees constructive interference, resulting in great enhancement in spectral brightness. I design and construct such a cavity-enhanced down-conversion source with record high spectral brightness, making it possible to use cold atoms as the interaction medium to achieve large nonlinearity between photons. The frequency of the photons is tunable and their coherence time is measured to be on the order of 10 nanoseconds, matching the lifetime of the excited state of typical alkali atoms. I characterize extensively the output of the source by measuring the second-order correlation function, quantifying two-photon indistinguishability, performing quantum state tomography of entangled states, and showing different statistics of the source. The unprecedented long coherence time of the photon pairs has also made possible the encoding of quantum information in the time domain of the photons. I present a theoretical proposal of multi-dimensional quantum information with such long-coherence-time photons and analyze its performance with realistic parameter settings. I implement this proposal with the quantum light source I have built, and show for the first time that a qutrit can be encoded in the time domain of the single photons. I demonstrate the coherence is preserved for the qutrit state, thus ruling out any classical probabilistic explanation of the experimental data. Such an encoding scheme provides an easy access to multi-dimensional systems and can be used as a versatile platform for many quantum information and quantum computation tasks.

Le travail présenté dans cette thèse est inspiré de précédents résultats sur les modèles de Gaudin ne contenant que des spins-1/2 (ces modèles sont intégrables) qui, par un changement de variable dans les équations de Bethe algébriques, parviennent à simplifier le traitement numérique de ces modèles. Cette optimisation numérique s'effectue par l'intermédiaire d'une construction en déterminant, ne dépendant que des variables précédemment mentionnées, pour chaque produit scalaire intervenant dans l'expression de la moyenne d'une observable à un temps donné. En montrant qu'il est possible d'utiliser la méthode du Quantum Inverse Scattering Method (QISM), même dans un cas où l'état du vide n'est pas état propre de la matrice de transfert, les résultats précédents concernant uniquement des spins-1/2 sont généralisés à des modèles contenant en plus une interaction spin-boson. De fait, cette généralisation a ouvert plusieurs voies de recherche possibles. Premièrement, il est montré qu'il est possible de continuer à généraliser l'utilisation de déterminants pour des modèles de spins décrivant l'interaction d'un spin de norme arbitraire avec des spins-1/2. La méthode permettant d'obtenir la construction des expressions explicites de ces déterminants est donnée. On peut également pousser la généralisation à d'autres modèles de Gaudin dont l'état du vide n'est pas état propre de la matrice de transfert. C'est ce que nous avons fait pour des spins-1/2 en interaction avec un champ magnétique dont l'orientation est arbitraire. Enfin, un traitement numérique de ces systèmes de spins-1/2 interagissant avec un mode bosonique est présenté. L'évolution temporelle de l'occupation bosonique et de l'aimantation locale des spins est ainsi étudiée selon deux Hamiltoniens différents, l'Hamiltonien de Tavis-Cummings et un Hamiltonien type spin central. Cette étude nous apprend que la dynamique de ces systèmes, qui relaxent d'un état initial vers un état stationnaire, conduit à un état superradiant lorsque l'état initial choisi y est favorable / The work presented in this thesis was inspired by precedent results on the Gaudin models (which are integrable) for spins-1/2 only which, by a change of variables in the algebraic Bethe equations, manage to considerably simplify the numerical treatment of such models. This numerical optimisation is carried out by the construction of determinants, only depending on the previously mentioned variables, for every scalar products appearing in the expression of the mean value of an observable of interest at a given time. By showing it is possible to use the Quantum Inverse Scattering Method (QISM), even when the vacuum state is not eigenstate of the transfer matrix, the previous results concerning spins-1/2 only are generalised to models including an additional spin-boson interaction. De facto, this generalisation opened different possible paths of research. First of all, we show that it is possible to further generalise the use of determinants for spin models describing the interaction of one spin of arbitrary norm with many spins-1/2. We give the method leading to the explicit construction of determinants’ expressions. Moreover, we can extend this work to other Gaudin models where the vacuum state is not an eigenstate of the transfer matrix. We did this work for spins-1/2 interacting with an arbitrarily oriented magnetic field. Finally, a numerical treatment of systems describing the interaction of many spins-1/2 with a single bosonic mode is presented. We study the time evolution of bosonic occupation and of local magnetisation for two different Hamiltonians, the Tavis-Cummings Hamiltonian and a central spin Hamiltonian. We learn that the dynamics of these systems, relaxing from an initial state to a stationary state, leads to a superradiant-like state for certain initial states

Pendant ces trois ans, nous nous sommes intéressés à quelques sujets choisis en optique et en électrodynamique quantiques. Le fil rouge de nos interrogations est la fonction d’onde du photon. Les expériences d’optique et d’électrodynamique quantique peuvent-elles être décrites de manière simple, dans l’espace des positions, à l’aide d’une fonction d’onde décrivant le ou les photon(s) impliqués dans l’expérience ? Ce n’est pas entièrement évident :la description usuelle des photons se fait dans l’espace réciproque des vecteurs d’onde. Mais ces expériences gagnent à être décrites par la mécanique ondulatoire en représentation position, comme cela est fait dans les manuels de mécanique quantique pour des situations impliquant des particules massives. De surcroît, une expérience récente[1] a conduit à l’observation de trajectoires de photons uniques à travers un interféromètre à deux fentes d’Young.Pour essayer de décrire formellement ces trajectoires, il est naturel de formuler une mécanique ondulatoire pour les photons. Nous avons donc examiné en détail la construction formelle de la fonction d’onde du photon, un objet qui est resté peu étudié jusqu’aux années 1990. Nous avons également étudié les propriétés de la fonction d’onde du photon en présence de sources, et considéré pour ce faire divers systèmes quantiques ouverts (en interaction). Nous avons vu qu’il existe, en principe, une infinité de possibilités pour le choix de la fonction d’onde du photon.Nous avons mis en évidence un certain nombre de critères sur la base desquels il apparaît que seuls trois choix parmi tous ceux possibles sont intéressants, l’un d’entre eux ramenant à un objet introduit par Glauber [2] pour étudier la détection de la lumière et les corrélations du champ électromagnétique. Nous avons également vu qu’en l’absence de sources l’équation quantique de propagation des photons est formellement identique aux équations de Maxwell.À bas nombre de photons, le formalisme de la fonction d’onde peut se révéler très pratique. Nous avons adapté l’approche aux systèmes en interaction, en nous intéressant dans un premier temps à l’électrodynamique quantique1en cavité [3], en particulier aux expériences réalisées par le groupe de Serge Haroche [4]. Nous avons proposé un modèle simple pour la description des photons dans les cavités d’électrodynamique. À l’aide de ce modèle, et de la fonction d’onde du photon, nous avons étudié la propagation des photons s’échappant de la cavité. Nous avons également construit l’équation maîtresse de Lindblad sans introduire de sauts quantiques non unitaires (voir également [5]). Nous nous sommes enfin intéressés à la question de l’évolution spatiotemporelle d’un photon émis lors d’une désexcitation d’un électron atomique. Après avoir étudié soigneusement la dynamique de la désexcitation de l’électron, notamment aux temps très courts [6, 7], nous nous sommes attachés à décrire, aussi rigoureusement que possible, le champ électromagnétique émis. Celui-ci, de manière surprenante, n’évolue pas causalement. Si cela n’est pas entièrement inattendu au vu du théorème de Hegerfeldt, qui stipule [8] que la causalité est exclue pour les systèmes décrits par un Hamiltonien dont le spectre est borné inférieurement, nous avons identifié [9] deux autres sources de non-causalité, l’une, prédite qualitativement par Shirokov [10], et l’autre, entièrement nouvelle à notre connaissance, et dont la compréhension reste à affiner. / During these three years we focused on several topics in quantum otpics and quantum electrodynamics. A central theme in our investigations is that of the photon wave function. Can quantum optics and quantum electrodynamics experiments be described simply, in position space, with the help of a wave function describing the photon(s) featured in the experiment ? The answer to that question is not quite obvious: the usual description of photons takes place in the reciprocal space of wave vectors. But these experiments call for a wave mechanical description in the position representation, as is done in quantum mechanics textbooks in situations featuring massive particles. Moreover, in a recent experiment [1], single photon trajectories through a Young two-slit setup have been observed. In order to try and describe these trajectories formally, it is natural to build a wave mechanical formalism for photons. We therefore studied in detail the formal construction of the photon wave function, an object which was little studied until the 1990s. We also studied the properties of the photon wave function in the presence of sources.To do that, we considered several open (interacting) quantum systems. We saw that there exists in principle an infinite number of possibilities when defining the photon wave function. We emphasised several criteria on the basis of which it appears that only three choices for the wave function are interesting. One of them coincides with an object introduced and used by Glauber [2] to study light detection andthe correlations of the electromagnetic field in the quantum regime. We also saw that, in the absence of sources, the propagation equation for a single photon is formally equivalent to Maxwell’s equations. At low photon numbers, the wave function formalism can be very useful. We adapted it to interacting systems,first, to cavity quantum electrodynamics (QED) [3], in particular to the experiments carried out by Serge Haroche’s group [4]. We proposed a simple model to describe photons in QED cavities. With this model, and with the helpof the photon wave function, we studied the propagation of photons escaping a cavity. We also constructed the Lindblad master equation without introducing nonunitary quantum jumps (also see [5]). We finally investigated the spacetime evolution of a photon which is emitted during the decay of an atomic electron. After having carefully studied the dynamics of the electronic decay, especially at very short times [6, 7], we set out to describe the emitted electromagnetic field as rigorously as possible. This emitted field, surprisingly, does not evolve causally. Though this is not entirely unexpected in view of Hegerfeldt’s theorem, which states [8] that causality is impossible for quantum systems which are described by a Hamiltonian with a spectrum which is bounded by below, we identified [9] two other sources of non causality. One of them was predicted qualitatively by Shirokov [10], while the other one, which is completely new as far as we can tell, is still to be better understood

This thesis describes the development of experimental methods to probe the nanoscale light-matter interactions in photonic and plasmonic nanostructures. The first part of this thesis presents the experimental findings on the temperature evolution of optical properties in important plasmonic materials. Understanding the influence of temperature on the optical properties of thin metal films - the material platforms for plasmonics - is crucial for the design and development of practical devices for high temperature applications in a variety of research avenues, including plasmonics, novel energy conversion technologies and near-field radiative heat transfer. We will first introduce a custom built experimental platform comprising a heating stage integrated into a spectroscopic ellipsometer setup that enables the determination of optical properties in the wavelength range from 370 nm to 2000 nm at elevated temperatures, from room temperature to 900 ^oC. Subsequently, the temperature dependent complex dielectric functions of gold, silver and titanium nitride thin films that were obtained using the above described experimental platform will be presented. Furthermore, the underlying microscopic physical processes governing the temperature evolution and the role of film thickness and crystallinity will be discussed. Finally, using extensive numerical simulations we will demonstrate the importance of incorporating the temperature induced deviations into numerical models for accurate multiphysics modeling of practical high temperature nanophotonic applications.<div><br></div><div>The second part of this thesis focuses on the development of experimental techniques to quantify the nanoscale steady-state energy distributions of plasmonic hot-carriers. Such hot-carriers have drawn significant research interest in recent times due to their potential in a number of applications including catalysis and novel photodetection schemes circumventing bandgap. However, direct experimental quantification of steady-state energy distributions of hot-carriers in nanostructures, which is critical for systemic progress, has not been possible. Here, we show that transport measurements from suitably chosen single molecular junctions can enable the quantification of plasmonic hot-carrier distributions generated via plasmon decay. The key idea is to create single molecule junctions - using carefully chosen molecules featuring sharp molecular resonances - between a plasmonic nanostructure and the gold tip of a scanning tunneling microscope, and quantify the hot-carrier distributions form the current flowing through the molecular junctions with and without plasmonic excitation at various voltage biases. Using this approach, we reveal the fundamental role of surface-scattering assisted absorption - Landau damping - and the contributions of different plasmonic modes towards hot-carrier generation in tightly confined nanostructures. The approach pioneered in this work can potentially enable nanoscale experimental quantification of plasmonic hot-carriers in key nanophotonic and plasmonic systems.<br></div>

Chromophore is a molecule or a part of a molecule which is responsible for its appearance color. This definition has been evolving over time with the progress of science. Contemporary scientific advances have expanded its meaning: to an inclusive level, chromophore is an irreducible collective of fundamental particles, which can represent the photophysical (optical physical) properties of the macroscopic matter. Previous studies have already found that the same molecule can have different photophysical properties under different condensed states. Therefore, it is straight forward to conclude that the definition of chromophore should take such extrinsic influencing interactions of this given molecule into consideration, thus simply taking the smallest unit such as a molecule is not accurate. A good example is quantum dots. Same species of quantum dots possess the identical smallest chemical unit but can emit very differently due to quantum confinement effect, thus defining the smallest unit as the chromophore is apparently fallacious. In solid polymeric compositions, the chemical unit or building blocks may differ from the spectroscopic unit depending on how these chemical units interacts within their ensemble to evolve new properties such as a new transition dipole. As thus, understanding the evolution of photophysical behaviors between the targeted unit and neighbors is of much importance to determine whether they should be considered as one chromophore or many. This requires a thorough understanding towards the evolution of photophysical properties of a collective, and the construction of such collective will need to pay extra attention to, as any structural factor could have changed some photophysical interactions of the collective. The introductory chapter discusses the material platform and fundamental photophysics investigated in this dissertation. Chromophore assembly (CA) as a sylloge of several classes of self-assembled materials, including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), porous organic polymers (POPs). Among them, MOF-based CAs (MOF-CAs) featuring with the ease of synthesis, demonstrate incomparable promises to construct such collective with several appealing characteristics, including component diversity, chemical stability, structural porosity, and post-synthetic versatility (Chapter 1.1). As for here, the main target to achieve using these assemblies is to understand the interaction between adjacent chemical monomeric units, therefore their spatial arrangements are of the paramount importance. As modern theory discovered, both ordered and random systems can be very important for novel quantum material developments. Both crystalline and amorphous arrangements of monomeric units can be achieved by adopting different classes of materials. MOF-CAs could achieve the precise control of spatial arrangement including distance, direction, and dihedral angle by its crystalline structures, whereas porous organic polymer-based CAs (POP-CAs) could feature a total randomness. Photophysics, as the research topic targeting the firsthand knowledge gained by interrogating the information provided by the propagating light after its interaction with matters, could provide crucial knowledge of the targeted matter. Hence, photophysical properties could provide fundamental understanding of the targeted matter (Chapter 1.2). State-of-the-art spectroscopic methods and instrumentation have made it possible to critically examine new structures to correlate photophysics with the chemical structure of their assemblies. By combining multiple spectroscopic techniques along with theoretical study, several correlations between the electronic properties of the matter, such as structural features, have been investigated. To illustrate, some unique topology-dependent photophysical behaviors found in chromophore assemblies are introduced (Chapter 1.3). In this dissertation, the feasibility of using specific types of MOF-CAs to conduct unique photophysical studies has been carefully chosen and verified (Chapter 2). Next, with the help of first principles computations, the nature of several electronic excited states as a function of different extent of Van der Waals or electronic interaction in MOF-CAs is unveiled, and experimentally studied with several environmental variates (Chapter 3). The knowledge was then articulated to devise a strategy to improve resonance energy transfer process in MOF-CAs. Here, low electronic symmetry of linker and directionally aligned transition dipoles of their collective ensembled are found beneficial to improve such photophysical process in a bottom-up manner (Chapter 4). Then, a series of MOFs were rationally designed to examine the feasibility and extent of a nonlinear excitonic process, singlet fission, to promote the generation of carriers usable for many applications including light-harvesting applications. The outcome demonstrated MOF-CA is a powerful tool to design such materials and is more capable in terms of its tunability (Chapter 5). At last, a set of randomly oriented CAs in POP were examined for underlying excited state dynamic process that highlights a thermal activated delayed fluorescence (TADF) involving S1 and low-lying T2 excited states (Chapter 6). This dissertation has highlighted unique yet tunable excited-state features and photophysical processes within the well-defined molecular ensemble realized via porous frameworks. These photophysical properties differ from those of their respective molecular system in their solubilized forms. Studies in this dissertation demonstrates a reliable platform to investigate multibody chromophore systems and suggested several valuable discoveries and lights the way for the study of novel chromophore assembly systems.