In Silico Estimation of Solvent Polarizabilities and Dipolarities

Area of Science:

• Computational chemistry
• Physical chemistry
• Spectroscopy

Background:

• Solvatochromism describes how a substance's color changes with solvent polarity.
• Understanding these changes is crucial for predicting dye behavior in different environments.
• Theoretical methods can complement experimental studies of solvatochromism.

Purpose of the Study:

• To theoretically investigate the solvatochromic behavior of beta-carotene and two cationic polymethine dyes (PD 2501, PD 1659).
• To assess the performance of TD-DFT calculations with different response models (LR-CPCM, cLR-CPCM, cLR2-CPCM) in predicting solvatochromic shifts.
• To establish in silico methods for estimating solvent properties.

Main Methods:

• Time-Dependent Density Functional Theory (TD-DFT) calculations were employed.
• Solvatochromic transition energies were computed for beta-carotene, PD 2501, and PD 1659 in ten solvents.
• Calculations were performed at three theoretical levels using linear-response (LR-CPCM) and corrected linear-response (cLR- and cLR2-CPCM) solvation models.

Main Results:

• Calculated transition energies for beta-carotene and PD 2501 correlated well (r² > 0.96) with medium polarizability (SP).
• Transition energies for PD 1659 showed strong correlations (r² > 0.93) with solvent dipolarity (SdP), independent of polarizability.
• Linear relationships were established between calculated energies and solvent scales.

Conclusions:

• TD-DFT calculations accurately predict solvatochromic behavior for these dyes.
• The study provides an in silico approach to estimate solvent polarizability and dipolarity.
• This method is valuable when experimental determination of solvent properties is challenging due to probe availability or solubility issues.