Exploring the photophysics of dibenzo[g,p]chrysene and tetraphenylethene in solution by static and dynamical quantum mechanical calculations.

Multichromophore assemblies (MCAs) of π-conjugated molecules exhibit complex photophysical behavior arising from the interplay between intra- and intermolecular interactions and environmental effects. In this work, we present a comprehensive computational study of two representative systems, dibenzo[g,p]chrysene (DBC) and tetraphenylethene (TPE), to elucidate how aggregation and environment influence their excited-state properties. By combining static quantum chemical calculations, vibronic simulations, nonadiabatic quantum dynamics within a linear vibronic coupling framework and fragment diabatization, we investigate their behavior from the gas phase to solution and aggregated states and, for DBC, compare it with the crystalline phase. For DBC, aggregation in solution has a limited effect on spectral features due to weak exciton coupling and strong localization of the excitation, whereas in the crystal the different stacking geometry leads to the expected H-aggregate behavior with distinct bright and dark states ordering. In contrast, in solution the closer packing enhances charge-transfer interactions, reversing the ordering of the low-lying states and altering the excited-state dynamics. For TPE, aggregation induces emission through a clear cage effect that restricts intramolecular motion, disfavoring nonradiative decay and stabilizing emissive states. Quantum dynamics simulations of the DBC dimer further show that, in solution, strong coupling to charge-transfer states can trap the population and hinder excitation energy transfer, while in the crystal weaker coupling favors more efficient exciton migration. Overall, our results highlight the critical role of structural constraints imposed by the environment in controlling photophysics, as well as the strengths and limitations of continuum solvation models, and demonstrate the power of quantum dynamics approaches for describing excited-state processes in molecular aggregates.