In Silico Estimation of Solvent Polarizabilities and Dipolarities

The solvatochromic behavior of β-carotene and of two analogous cationic polymethine dyes with distinct chain-lengths (PD 2501 and PD 1659) was investigated theoretically by means of TD-DFT calculations of their solvatochromic transition energies in ten solvents, at three levels of theory, with linear-response (LR-CPCM) and corrected linear-response (cLR- and cLR²-CPCM) approaches. The calculated transition energies of β-carotene and of PD 2501 showed good correlations (r² > 0.96) with the values of the medium polarizability (SP). Calculated transition energies of PD 1659 showed equally good correlations (r² > 0.93) with the values of the solvent dipolarity (SdP), without contamination by the medium polarizabilities. The obtained linear relationships with the SP and SdP scales thus offer an in silico alternative for estimating medium polarizabilities and dipolarities of new solvents or solvent mixtures in cases where the varieties of probes employed for their determination are not available or show solubility problems.