Dielectric-tuned charge and exciton dynamics in perylene bisimide supramolecular aggregates

Optimizing charge separation and transport in supramolecular architectures is critical for advancing artificial photosynthesis and organic optoelectronics. However, disentangling the effects of the dielectric environment from structural reorganization remains a challenge due to the intrinsic complexity of these systems. Here, we report the dielectric-tuned charge and exciton dynamics in a structurally robust perylene bisimide H-aggregate that maintains its packing geometry regardless of solvent polarity. By performing solvent-polarity-dependent transient absorption experiments, we observe a fundamental mechanistic crossover of charge dynamics dictated by the dielectric medium: in nonpolar environments, reaction kinetics are driven by quantum tunneling via high-frequency vibrational modes (semiclassical regime), whereas in polar environments, they are gated by collective solvent fluctuations (classical regime). Furthermore, pump-fluence-dependent measurements show that charge separation from excimer-like S₁ excitons competes with exciton-exciton annihilation, leading to solvent-polarity-dependent diffusion lengths, whereas the generated charge carriers display non-diffusive behavior. These findings provide an analytical framework for distinguishing between vibrationally-assisted or solvent-controlled electron transfer, offering a roadmap for engineering efficient charge and exciton transport in organic semiconducting molecular assemblies.