Identifying electron transfer coordinates in Donor-Bridge-Acceptor systems using mode projection analysis

摘要

We report upon an analysis of the vibrational modes that couple and drive the state-to-state electronicudtransfer branching ratios in a model donor-bridge-acceptor system consisting of a phenothiazine-based donorudlinked to a naphthalene-monoimide acceptor via a platinum-acetylide bridging unit. Our analysis is basedudupon an iterative Lanczos search algorithm that finds superpositions of vibronic modes that optimize theudelectron/nuclear coupling using input from excited-state quantum chemical methods. Our results indicateudthat the electron transfer reaction coordinates between a triplet charge transfer state and lower lying chargeseparatedudand localised excitonic states are dominated by asymmetric and symmetric modes of the acetyleneudgroups on either side of the central atom in this system. In particular, we find that while a nearly symmetricudmode couples both the charge-separation and charge-recombination transitions more or less equally, theudcoupling along an asymmetric mode is far greater suggesting that IR excitation of the acetylene modesudpreferentially enhances charge recombination transition relative to charge-separation.