Quantum Chemical Modeling of Optical and Physicochemical Properties of Amphiphilic Spiropyranes

The time-dependent density functional theory (TD-DFT) method was used for the first time to calculate electronic transitions of amphiphilic spiro compounds. It is shown that it gives a fundamentally correct electron density distribution, corresponding to the results obtained using the CASSCF method, and allows one to predict the nature of the electronic transition of the merocyanine form. For negative photochromes, the possibility of the existence of conical intersections of the potential energy surfaces of the ground and excited electronic states has been discovered, which may be the reason for the slow photochromism of these compounds. The fundamental possibility of using TD-DFT to predict the optical characteristics of long-chain spiropyrans is demonstrated, provided that scaling regressions are used. For the first time, linear regressions have been developed for such compounds, taking into account a set of physical parameters of the solvent in explicit form. This made it possible to obtain a unified empirical correction that takes into account the solvatochromic effect. The results obtained can be used as a basis for developing a main concept that takes into account the effect of the solvent on the spectral properties of spiro compounds and for constructing a unified regression model covering various types of solvato- and photochromism.