Dissecting the nature of exciton interactions in ethyne-linked tetraarylporphyrin arrays

Abstract

We investigate how electronic energy transfer in a series of three ethyne-linked Zinc- and free base-tetraarylporphyrin dimers is tuned by the type of linker and by substitution on the porphyrin rings. We use TD-DFT combined with a recently developed fully polarizable QM/MM/PCM method. This allows us to dissect the bridge-mediated contributions to energy transfer in terms of superexchange (through-bond) interactions and Coulomb (through space) terms mediated by the polarizability of the bridge. We explore the effects of the substituents and of the bridge-chromophore mutual orientation on these contributions. We find that bridge-mediated superexchange contributions largely boost energy transfer between the porphyrin units. When the effect of the solvent is also considered through PCM, we find good agreement with the through-bond versus through-space contributions determined experimentally, thus indicating the need to properly include both solvent and bridge effects in the study of energy transfer in bridged molecular dyads.