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Abstract

We show that molecular aggregation can strongly influence the nonradiative decay (NRD) lifetime of an electronic excitation. As a demonstrative example, we consider a transition-dipole-dipole-interacting dimer whose monomers have harmonic potential energy surfaces (PESs). Depending on the position of the NRD channel (q(nr)), we find that the NRD lifetime (tau(dim)(nr)) can exhibit a completely different dependence on the intermolecular-interaction strength. We observe that (i) for q(nr) near the Franck-Condon region, tau(dim)(nr) increases with the interaction strength; (ii) for q(nr) near the minimum of the monomer excited PES, the intermolecular interaction has little influence on tau(dim)(nr); and (iii) for q(nr) near the classical turning point of the monomer nuclear dynamics, on the other side of the minimum, tau(dim)(nr) decreases with the interaction strength. Our findings suggest design principles for molecular systems where a specific fluorescence quantum yield is desired.