Tuning nonradiative lifetimes via molecular aggregation

TL;DR

This study demonstrates how molecular aggregation can significantly alter nonradiative decay lifetimes, providing insights for designing molecular systems with tailored fluorescence properties.

Contribution

It reveals the dependence of nonradiative decay lifetimes on intermolecular interactions and NRD channel positions in a dimer model, offering new design principles.

Findings

NRD lifetime increases with interaction strength near the Franck-Condon region

NRD lifetime is unaffected by interaction near the monomer excited PES minimum

NRD lifetime decreases with interaction near the classical turning point

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 ($q_{\rm nr}$), we find that the NRD lifetime ($\tau_{\rm nr}^{\rm dim}$) can exhibit a completely different dependence on the intermolecular-interaction strength. We observe that (i) for $q_{\rm nr}$ near the Franck-Condon region, $\tau_{\rm nr}^{\rm dim}$ increases with the interaction strength; (ii) for $q_{\rm nr}$ near the minimum of the monomer excited PES, the intermolecular interaction has little influence on $\tau_{\rm nr}^{\rm dim}$; (iii) for $q_{\rm nr}$ near the classical turning point of the monomer nuclear dynamics, on the other side of the minimum, $\tau_{\rm nr}^{\rm dim}$ decreases with the interaction strength. Our findings suggest design principles for molecular systems where a specific fluorescence quantum yield is desired.