The role of proton configurations in the absorption characteristics of trefoil-shaped Salicylaldehyde Azine derivatives: The electronic structure calculation analysis.

In this study, we investigated the influence of proton configurations and molecular symmetry on the stability and absorption characteristics of trefoil-shaped salicylaldehyde azine derivatives synthesized by Naito et al.. Our energy comparisons revealed that the most stable proton configurations differ significantly between the ground and S₁ excited states. While the most stable ground-state structure did not exhibit absorption peaks in the experimentally observed region above 400 nm, the optimized stable configurations in the S₁ excited state did show prominent spectral features at these longer wavelengths. Further analysis of activation energies indicated that the structural transition between these configurations is energetically feasible in the S₁ excited state, suggesting facile proton rearrangements upon excitation. Classical molecular dynamics simulations demonstrated that structural distortions induced by thermal fluctuations also result in significant absorption at wavelengths beyond 400 nm. Additionally, solvent effects were found to induce a red shift in absorption spectra, although this influence was relatively minor compared to that arising from structural distortions. Changes in molecular symmetry were found to have only a negligible effect on spectral properties. These findings suggest that proton rearrangement and structural relaxation play critical roles in generating absorption at longer wavelengths.