Frenkel excitons in : excitation energy transfer and exciton coherence

Abstract

A review is presented about sensitized luminescence and luminescence lineshape studies on pure and doped sodium nitrite which have led to detailed knowledge about the lowest excited states of this system. Both the lowest triplet state and the first excited singlet state are Frenkel excitons, states that can migrate through the crystal. This migration is appropriately described by a one-dimensional energy transfer process for the triplet and, surprisingly, also for the singlet state. The exciton states themselves show an evolution in time that reveal the transition from coherent to incoherent behaviour with increasing temperature. In combination with theoretical investigations a consistent picture of the exciton states in sodium nitrite is achieved.

Potential Applications for Solar Photocatalysis: From Environmental Remediation to Energy Conversion

“…The batochromic shift of the absorption maximum associated to Q band, suggests the occurrence of Frenkel's J aggregates of ZnPc (Fig. 5) in the composites (Köhler & Schmid, 1996;Eisfeld & Briggs, 2006;, which agrees with results of a theoretical study employing methods of Density Functional Theory on the formation of aggregates of zinc phthalocyanine (Machado et al, 2011a). The bathochromic shift of the absorption maximum of the Q band highlights the differentiated nature of these compounds against pure TiO 2 and ZnPc.…”

The Electronically Excited States of LH2 Complexes from Rhodopseudomonas acidophila Strain 10050 Studied by Time-Resolved Spectroscopy and Dynamic Monte Carlo Simulations. II. Homo-Arrays Of LH2 Complexes Reconstituted Into Phospholipid Model Membranes

“…The simulations reveal that the amplitude of the fast decay component is the larger, the closer the shape of the cluster resembles a quadratic arrangement of the LH2 complexes. This shows that the energy transfer efficiency depends on the dimensionality of the transfer process, which is a well-known phenomenon seen in exciton migration in molecular crystals. − There it was found that the lower the dimensionality of the energy transfer process, the lower the chance that two excitations meet on the same crystal site, which means that losses due to singlet–singlet annihilation are less probable for a (close to) one-dimensional alignment of the LH2 complexes. It is interesting to speculate whether this finding might be of relevance for the architecture of the natural photosynthetic unit. − From these model calculations, it becomes apparent, that variations in the size and/or shape of the clusters result in a distribution of the amplitude of the fast decay component of the fluorescent transients.…”

Energy Transfer and Spectroscopic Characterization of Multichromophoric Assemblies

“…An understanding of the interactions between chromophores when one has been photoexcited (recently the subject of renewed investigation − ) is of fundamental importance in a diversity of studies and applications in photophysics. Some recent examples in this broad field range from investigations of intramolecular energy transfer in bichromophores to studies of light harvesting antenna systems in photosynthetic bacteria, higher plants, synthetic multichromophoric assemblies, and solid state systems . The phenomenon is used also to characterize the structure of various systems, especially in polymer and biological fields …”

“…Some recent examples in this broad field range from investigations of intramolecular energy transfer in bichromophores 5 to studies of light harvesting antenna systems in photosynthetic bacteria, 6 higher plants, 7 synthetic multichromophoric assemblies, 8 and solid state systems. 9 The phenomenon is used also to characterize the structure of various systems, especially in polymer 10 and biological fields. 11 The optical properties of assemblies of interacting chromophores were described by Fo ¨rster 12 as "nonadditive", since photophysical properties of the aggregate system (i.e., consisting of two or more chromophores) may be quite different from those of the components.…”