Motivated by distinct solid-state luminescence properties of two benzene dicarboxyl acid crystals, TPA and IPA, we have systematically explored their excited-state relaxation mechanisms in solution and crystal environments. Given the weak interactions between π -π stacked dimers, the exciton couplings in both molecules are very small compared to the reorganization energies associated with exciton transport. As a result, excited-state processes are primarily localized on individual molecules, and exciton transport occurs predominantly through incoherent exciton hopping between single molecules.