Explicit versus Implicit Solvation Effects on the First Hyperpolarizability of an Organic Biphotochrome

The first hyperpolarizability of the four trans forms of a dithienylethene indolinooxazolidine biphotochrome in acetonitrile solution has been evaluated by using two solvation models, an explicit and an implicit one. The implicit solvation model is the integral equation formalism of the polarizable continuum model (IEF-PCM), whereas in the explicit one, the solvent molecules are represented by point charges, of which the positions have been generated by Monte Carlo simulations whereas the solute is treated quantum mechanically. At optical frequencies, first hyperpolarizabilities calculated with the implicit solvation model are usually larger than those obtained with the multiscale approach. However, both approaches predict similar contrasts, indicating that implicit solvation models such as IEF-PCM are well-suited to describe the variations in the NLO responses of molecular switches. In addition, the analysis of the contrasts of first hyperpolarizabilities shows that the biphotochrome can act as a three-state NLO switch.