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The ability to undergo spin-allowed exciton multiplication makes singlet fission materials promising for photovoltaic applications. Here, we examine the separation of correlated triplet pairs, (1)(T...T), in polycrystalline pentacene films via temperature-dependent transient absorption spectroscopy. Single wavelength analysis reveals a profound delay in [.sup.1](T...T) dynamics. Moreover, the dynamics of [.sup.1](T...T) exhibit temperature dependence, whereas other features show no discernable temperature dependence. Previous literatures have suggested that correlated triplet separation is mediated by a thermally activated hopping process. Surprisingly, we found that the time constants governing triplet pair separation display two distinct temperature-dependent regimes of triplet transport. The high temperature regime follows a thermally activated hopping mechanism. The experimentally derived reorganization energy and electronic coupling is verified by density matrix renormalization group quantum chemical calculations. In addition, we evaluated the low temperature regime and show that the trend can be modelled by a Miller-Abrahams-type model that incorporates the effects of energetic disorder. We conclude that the correlated triplet pair separation is mediated by thermally activated hopping or a disorder driven Miller-Abrahams-type mechanism at high and low temperature, respectively. We observe that crossover between two regimes occurs ~226 K. We find the time constant for triplet-triplet energy transfer to be 1.8 ps at ambient temperature and 21 ps at 77 K. Key words: pentacene, spin entanglement, disorder, thermal activation, Miller-Abrahams transport, Marcus theory. La capacite des excitons a subir une multiplication permise par le spin rend les materiaux a fission d'excitons singulet prometteurs dans le contexte d'applications en photovoltaique. Dans le cadre des presents travaux, nous avons examine la separation des paires triplet correlees [.sup.1](T...T) dans des films de pentacene polycristallin par spectroscopie d'absorption transitoire dependante de la temperature. L'analyse a differentes longueurs d'onde a montre un delai considerable dans la dynamique des paires [.sup.1](T... T). Par ailleurs, cette dynamique des paires [.sup.1](T... T) s'est revelee dependante de la temperature, alors que d'autres caracteristiques ne montrent aucune dependance notable en fonction de la temperature. Des publications anterieures ont avance l'hypothese que la separation de paires triplet correlees s'effectue par un processus de saut active thermiquement. Etonnamment, nous avons constate que les constantes temporelles regissant la separation des paires triplet montrent deux regimes distincts de transport de triplets dependants de la temperature. Le regime a haute temperature suit un mecanisme de saut active thermiquement. L'energie de reorganisation et le couplage electronique derives experimentalement ont ete verifies par calculs de chimie quantique sur le groupe de normalisation de la matrice densite. De plus, nous avons evalue le regime a basse temperature et nous avons montre que la tendance pouvait etre modelisee selon un modele de type Miller-Abrahams qui tient compte des effets du desordre energetique. Nous avons conclu que la separation de paires triplet correlees procede selon un saut active thermiquement a haute temperature ou selon un mecanisme de type Miller-Abrahams gouverne par le desordre a basse temperature. Par ailleurs, nous avons observe que le croisement entre les deux regimes se produit autour de 226 K. Nos resultats montrent que la constante temporelle du transfert d'energie triplet-triplet est de 1,8 ps a temperature ambiante et de 21 ps a 77 K. [Traduit par la Redaction] Mots-cles: pentacene, enchevetrement de spins, desordre, activation thermique, transport Miller-Abrahams, theorie de Marcus., Introduction Triplet excitons have been demonstrated to play a key role in numerous photochemical processes including thermally activated delayed fluorescence (TADF), triplet--triplet annihilation (TTA), and singlet fission. Utilizing triplet excitons [...]

Exciton interactions in rigidly linked dinaphthyl molecules were evaluated basing on through-space and through-bond effects. Resonance splitting of naphthalene was shown and found to be greater than predicted by the usual dipole-dipole model. The role of the through-space interchromophore orbital was found to be insignificant while the through-bond interaction exerts an important role in the efficient delocalization of the excitation observed.

The solution-phase formation of ordered lamellar nanocrystal (NC) arrays is described, where the semiconductor lamellae has displayed structural integrity and temporal stability, without recourse to chemical cross-linking. The encapsulation of gold nanoparticles has caused photoluminescence enhancement of the host CdSe nanocrystals.

A seeded growth method based solely on different sized CdTe seeds was used to prepare type II CdTe-CdSe colloidal nanocrystal heterostructures in a variety of shapes (fat rods, Y-shape rods, and tetrapods). The tailored shape of nanocrystal heterostructures provide a new pathway to modify interfacial charge-transfer and radiative recombination in the near-infrared region.

A simple and versatile approach is described for achieving spatially defined organization of colloidal CdSe, CdSe/ZnS core/shell, or PbS nanocrystals with poly(3-hexylthiophenes) (P3HTs) by using micelles of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) as the main structural motif. The spatially defined organization of the active components has provided new opportunities for analyzing the complicated photophysics intrinsic to blends of nanoscale systems, such as bulk heterojunctions by establishing simplified and better controlled interfaces.

A new type of cylindrical micelle architecture is prepared with an A-B-A triblock structure bearing spatially controlled coronal charge. Electrostatic interactions are used for functionalizing the new nanomaterials with Au and PbS nanoparticles in a spatially selective manner to afford novel composite structures.

The dynamics of interchain and intrachain excitation energy transfer taking place in a polyindenofluorene endcapped with perylene derivatives is explored by means of ultrafast spectroscopy combined with correlated quantum-chemical calculations. Reports reveal faster exciton migration in films with respect to solution as a result of the emergence of efficient channels involves hopping between chains in close contact.

The molecular Resonance Energy Transfer (RET) and the recent development in the field are described. As a result of the introduction of some new principles underlying RET processes, many of the important concepts are covered together into a generalization of Foster's original theory.

A ligand exchange method to modify nanocrystals (NCs) with a polydimethylaminoethly methacrylate (PDMAEMA) is developed. This method highlights utility of using simple homopolymers that can synthesize in a controlled manner.

The mechanisms controlling excitation energy transport (EET) in light-harvesting complexes remain controversial. Following the observation of long-lived beats in 2D electronic spectroscopy of PC645, vibronic coherence, the delocalization of excited states between pigments supported by a resonant vibration, has been proposed to enable direct excitation transport from the highest-energy to the lowest-energy pigments, bypassing a collection of intermediate states. Here, we instead show that for phycobiliprotein PC645 an incoherent vibronic transport mechanism is at play. We quantify the solvation dynamics of individual pigments using ab initio quantum mechanics/molecular mechanics (QM/MM) nuclear dynamics. Our atomistic spectral densities reproduce experimental observations ranging from absorption and fluorescence spectra to the timescales and selectivity of down-conversion observed in transient absorption measurements. We construct a general model for vibronic dimers and establish the parameter regimes of coherent and incoherent vibronic transport. We demonstrate that direct down-conversion in PC645 proceeds incoherently, enhanced by large reorganization energies and a broad collection of high-frequency vibrations. We suggest that a similar incoherent mechanism is appropriate across phycobiliproteins and represents a potential design principle for nanoscale control of EET.

Coherence phenomena arise from interference, or the addition, of wave-like amplitudes with defined phase. While coherence has been shown to yield transformative new ways for improving function, advances have been limited to pristine matter, as quantum coherence is considered fragile. Recent evidence of coherence in chemical and biological systems, however, suggests that the phenomena are robust and can survive in the face of disorder and noise. Here we survey the state of recent discoveries, present viewpoints that suggest coherence can be used in complex chemical systems, and discuss the role of function as a design element in realizing coherence., Chemistry and Chemical Biology