<p>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.</p>