Synthetic Control of Exciton Dynamics in Bioinspired CofacialPorphyrin Dimers

Understanding how the complex interplay among excitonic interactions, vibronic couplings, and reorganization energy determines coherence-enabled transport mechanisms is a grand challenge with both foundational implications and potential payoffs for energy science. We use a combined experimental and theoretical approach to show how a modest change in structure may be used to modify the exciton delocalization, tune electronic and vibrational coherences, and alter the mechanism of exciton transfer in covalently linked cofacial Zn-porphyrin dimers (meso-betalinkedABm-beta andmeso-mesolinkedAAm-m). While bothABm-beta andAAm-mfeature zinc porphyrins linked by a 1,2-phenylenebridge, differences in the interporphyrin connectivity set the lateralshift between macrocycles, reducing electronic coupling inABm-beta and resulting in a localized exciton. Pump-probe experiments show that the exciton dynamics is faster by almost an order ofmagnitude in the strongly coupledAAm-mdimer, and two-dimensional electronic spectroscopy (2DES) identifies a vibroniccoherence that is absent inABm-beta. Theoretical studies indicate how the interchromophore interactions in these structures, and theirsystem-bath couplings, influence excitonic delocalization and vibronic coherence-enabled rapid exciton transport dynamics. Real-time path integral calculations reproduce the exciton transfer kinetics observed experimentally and find that the linking-modulated exciton delocalization strongly enhances the contribution of vibronic coherences to the exciton transfer mechanism, and that this coherence accelerates the exciton transfer dynamics. These benchmark molecular design, 2DES, and theoretical studies provide a foundation for directed explorations of nonclassical effects on exciton dynamics in multiporphyrin assemblies

Automated summary

This study combines experimental and theoretical approaches to modify exciton delocalization, tune electronic and vibrational coherences, and alter the mechanism of exciton transfer. The results show that differences in structure affect the dynamics and coherence of excitons. Theoretical studies explain how interchromophore interactions and couplings influence exciton delocalization and rapid exciton transfer dynamics.