Dissecting the Nature of Exciton Interactions in Ethyne-Linked Tetraarylporphyrin Arrays

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 time-dependent density functional theory (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 the polarizable continuum model (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.