Theoretical-computational modeling of the vibrational chirality of interacting chromophores: VCD signal and equilibrium properties of excitonic <i>clusters</i>

In this work, we extend the perturbed matrix method combined with molecular dynamics simulations, to the modeling of Vibrational Circular Dichroism (VCD) spectra, including non-covalent excitonic coupling among distinct molecular chromophores. The method is applied to (R)-propylene oxide as a benchmark system, comparing infinite-dilution conditions with highly concentrated solutions in water and carbon tetrachloride. The calculated VCD spectra show very good agreement with experimental data and only weak concentration dependence. However, analysis of the excitonic eigenstates reveals the formation of transient, thermally populated excitonic clusters characterized by delocalized vibrational excitations and widely dispersed rotatory strengths. The equilibrium distribution and free-energy profile of these clusters are characterized, providing microscopic insights into excitonic effects in VCD spectra of soft condensed-phase systems.