Development of the energy flow in light-harvesting dendrimers

Abstract

Modeling the multistep flow of energy in light-harvesting dendrimers presents a considerable challenge. Recent studies have introduced an operator approach based on a matrix representation of the connectivity between constituent chromophores. Following a review of the theory, detailed applications are now shown to exhibit the time development of the core excitation following pulsed laser irradiation and the steady-state behavior that can be expected under conditions of constant illumination. It is also shown how energy capture by whole dendrimers can be analytically related to chromophore pair-transfer properties and, in particular, the spectroscopic gradient toward the core. Indicative calculations also illustrate the consequences of tertiary folding. In each respect, the model affords opportunities to derive new, physically meaningful information on the photophysical and structural features of dendrimeric systems.

Resonance energy transfer: Influence of neighboring matter absorbing in the wavelength region of the acceptor

“…In many photobacterial systems based on bacteriochlorophyll B800 and B850 (the numerals denoting absorption maxima in nanometers), it is well understood that B800 chromophores commonly absorb light of this wavelength and then pass excitation on to a B850, when both are in the same vicinity. 4 The corresponding spectroscopic gradient, 5 which is offset by minor vibrational losses, serves to impart a significant degree of directionality to the energy routing. Although it might be supposed that replacing the B800 with B850 might achieve the same end in a system of reduced complexity, higher densities of B850 could promote singlet-singlet annihilation and exciton formation.…”

Mechanisms of Light Energy Harvesting in Dendrimers and Hyperbranched Polymers

“…It is well-known that even small departures from planarity, associated with three-dimensional folding of the dendrimer structure, can displace peripheral chromophores sufficiently to produce significant modifications in the dynamics of energy transfer [79]. One of the upshots is that multi-step transfer may not necessarily proceed by the most direct route; folding can facilitate transfers of energy, between chromophores in close proximity, that do not expedite an overall progress of energy towards the core.…”

“…Using essentially classical methods of representing energy flow as a series of stepwise processes, Knoester et al [77,78] and also Andrews et al [79][80][81] have explored the relationships between trapping times and the connectivity of dendrimers. Nonetheless, the formulation of each such step requires quantum methods.…”

Dynamics of the dispersion interaction in an energy transfer system

“…One of its most widely studied manifestations is the process of energy hopping between chromophores within light-harvesting complexes-both natural [1][2][3][4][5] and synthetic polymers such as dendrimers. 3,[6][7][8][9] In the latter connection we have recently reported the results of several calculations on energy flow [10][11][12] and competing two-photon processes. 13 Beyond the sphere of dendrimers, RET has been employed to determine a wide range of other polymeric properties; the 'spectroscopic ruler' has been readily utilised as a means of elucidating physical and morphological interface properties in complex polymer blends, for example.…”