Description of Solvatochromism of Peak Broadening in Absorption Spectra in Solution Using the Reference Interaction Site Model Self-Consistent Fields Spatial Electron Density Distribution

Abstract

We quantified and subsequently analyzed bandwidth of ultraviolet and visible photoabsorption spectral lines in solution by applying time-dependent first-order perturbation theory using the Born–Oppenheimer adiabatic potential calculated using the multistate extended-multi-configurational quasi-degenerated second-order perturbation theory (MS-XMCQDPT2) coupled with the reference interaction site model self-consistent field spatial electron density distribution (RISM-SCF-cSED). The proposed method was implemented for 2-thiocytosine in solution, and solvatochromism of the bandwidth of the π S π* transition was clearly observed. The standard deviation of a characteristic electronic excitation was decomposed into the contributions of the characteristic vibrational mode of 2-thiocytosine. The main vibrational modes contributing to peak broadening were found to be for acetonitrile, methanol, and the aqueous phase. We concluded that the mechanism for peak broadening is qualitatively different for phases of protic and aprotic solvents because of the structural variation in 2-thiocytosine driven by the breakage of the resonance structures.

Vibrational Self-Consistent Field (VSCF) and Post-VSCF Method Calculations Combined with the Reference Interaction Site Model Self-Consistent Field Method Coupled with the Constrained Spatial Electron Density Distribution: Applications to NaHCOO in Aqueous Phase

“…To address these challenges, we have developed quantum chemical computations using the reference interaction site model self-consistent field method in conjunction with the constrained spatial electron density distribution (RISM–SCF–cSED). , This method combines principles from both quantum and statistical mechanics and has demonstrated versatility across various solvent systems, encompassing protic and aprotic solvents and supercritical water (SCW) systems. − In a previous investigation, we successfully expounded upon the minor nonlinear Raman shift (∼10 cm –1 ) observed in the CN stretching vibration of p -aminobenzonitrile ( p -ABN) relative to the reduced density of SCW . Additionally, we elucidated the changes in Raman intensity exhibited by p -nitroaniline ( p NA) under different solvent environments, including SCW …”