Structures and Spectroscopic Properties of Polysulfide Radical Anions: A Theoretical Perspective

Area of Science:

• Inorganic Chemistry
• Theoretical Chemistry
• Spectroscopy

Background:

• Polysulfide radical anions (S_n^•-) are crucial in elemental sulfur chemistry.
• Spectroscopic data for larger S_n^•- (n=4-8) are limited, hindering their identification.

Purpose of the Study:

• To computationally determine the preferred geometries of S_n^•- (n=4-8) in polar media.
• To predict the electronic excitation energies and optical characteristics of these larger polysulfide radical anions.

Main Methods:

• Density Functional Theory (DFT) calculations with PCM correction for geometry optimization.
• Time-Dependent DFT (TD-DFT) for calculating electronic excitation energies.
• Validation of the computational approach using experimental data for S₂^•- and S₃^•-.

Main Results:

• Predicted geometries for S_n^•- (n=4-8) in polar environments.
• Calculated electronic excitations, revealing distinct spectral features for acyclic (S₄^•-, S₅^•-) and quasi-cyclic (S₆^•- to S₈^•-) structures.
• Explanation of near-IR transitions for acyclic species via HMO π-only model and σ → σ* processes for cyclic species.

Conclusions:

• The study provides essential computational data for identifying larger polysulfide radical anions.
• Understanding the electronic transitions aids in characterizing these transient species in sulfur chemistry.
• The findings extend the theoretical framework for polysulfide radical anion spectroscopy.