Photoactive arrays at high levels of optical excitation: the effects of chromophore geometry and polarisability

Summary form only given. At high levels of optical illumination, multichromophore arrays can exhibit a novel form of resonance energy transfer involving the coupling of two excited donor chromophores (A and A´) and one neighbouring acceptor chromophore (B) in its electronic ground state. This trichromophore effect is the subject of an investigation into the dependence on the mutual positions and orientations of the participating chromophores. Employing methods similar to those well-known in bimolecular photophysics, comparisons are made between pairwise resonance energy transfer and the novel three-body analogue, with counterparts to the conventional orientation factor identified. By the scrutiny of molecular architectures based on linear configurations (either A-B-A´ or A-A´-B), the interplay of the orientation factors is analysed. The relative dominance of cooperative and accretive mechanisms over energy pooling rates is comprehensively analysed, only special cases having been discussed in initial studies. The relative alignments and magnitudes of the donor and acceptor transition moments and polarisabilities are also shown to have a profound effect on achievable pooling efficiency, with reference to particular alignments and intermolecular vectors. The delineation presented should give direction to suitable methods of investigation into the performance and geometric optimisation of such arrays at high levels of illumination.