Vibrational solvatochromism: towards systematic approach to modeling solvation phenomena

Area of Science:

• Computational Chemistry
• Spectroscopy
• Physical Chemistry

Background:

• Vibrational solvatochromic frequency shift arises from local electric field interactions with IR probes in condensed phases.
• Empirical models for vibrational shifts and transition dipoles exist, but a systematic ab initio approach for calculating vibrational solvatochromic charges and multipoles is lacking.

Purpose of the Study:

• To develop and apply a systematic ab initio method for calculating vibrational solvatochromic charges and multipoles.
• To investigate the frequency shifts of N-methylacetamide (NMA) in condensed phases using density functional theory (DFT).

Main Methods:

• Utilized density functional theory (DFT) calculations for N-methylacetamide (NMA).
• Employed implicit and coarse-grained models for solvation.
• Applied distributed multipole analysis (DMA) of electronic densities for gas-phase NMA.
• Calculated amide I vibrational frequency shifts in water clusters mimicking liquid water configurations.

Main Results:

• Solvatochromic infrared spectral shifts were estimated based on distributed multipole analysis.
• The calculated spectral shifts were primarily electrostatic.
• The proposed model reproduced DFT results with semi-quantitative accuracy.

Conclusions:

• A systematic ab initio approach for calculating vibrational solvatochromic charges and multipoles has been developed.
• The electrostatic nature of spectral shifts was confirmed.
• The method provides a quantitative tool for predicting vibrational frequency shifts in condensed phases.