Solvent effects on g-tensors of semiquinone radical anions:: polarizable continuum versus cluster models

Density functional theory has been applied to study environmental effects on electronic g-tensors of a series of 1,4 semiquinone radical anions. In particular, solvent effects on solute structure, spin density distribution, and g-tensor have been investigated using both the conductor-like polarizable continuum model (CPCM) and explicit cluster solvent models. For protic solvents, the CPCM calculations provide solvent effects in qualitative but not in quantitative agreement with experiment. Explicit inclusion of solvent molecules hydrogen-bonded to the semiquinone oxygen atoms is required to obtain a more quantitative description. Available experimental g-tensor data in aprotic solvents are insufficient to judge adequately the performance of the CPCM calculations. However, the present data should serve to calibrate future experimental electron paramagnetic resonance studies. Detailed molecular-orbital analyses of the solvent influences on the g-tensors of various semiquinone radical anions are provided.