Comprehensive PCM and QM/MM-MD investigation of absorption and emission properties in N-methylindoles

This study investigates the absorption and emission behavior of N-Methylindoles (N = 1-7) in aqueous solution, aiming to understand how solvent dynamics influence photophysical properties. A range of solvent modeling approaches (including PCM Linear Response, PCM State Specific, QM/MM Static, QM/MM Dynamic, and QM/ MM/MD Nonequilibrium) were evaluated for their ability to reproduce experimentally recorded spectra. Our absorption spectral analysis demonstrates that the QM/MM-MD approach offers the most accurate agreement with experiment, capturing the influence of solvent reorganization and ultrafast solute-solvent interactions that static and implicit models fail to fully describe. Notably, excited-state equilibration occurs nearly twice as fast as in the ground state, attributed to solvent response to changes in solute surface accessibility. The emission properties, on the other hand, can be simulated more effectively using PCM methods than QM/MM approaches. Visualization via reduced density gradient (RDG) analysis and radial distribution functions (RDF) reveal significant differences in polar and nonpolar solute-solvent interactions between electronic states. These findings underscore the importance of dynamic and state-specific solvent effects in accurately modeling photophysical processes in polar protic environments.