On the Influence of the Solvent Medium on Molecular Spectra: Chrysazin Radical Anion and Anthanthrene

For instance, analysis of the ESR spectra of semiquinone radical anions is frequently complicated by a strong influence of the solvent, occasionally leading to suggestions in the literature of divergent assignments of the hyperfine constants to distinct positions [1]. One example is chrysazin semiquinone [2]. In the present investigation [3], solvation of this radical anion was studied by Density Functional Theory (DFT) calculations: In one series of calculations, the influence of the solvent was approximated by the Isodensity Polarizable Continuum Model (IPCM) [4]. In a second series, protic solvation was simulated within a super-molecule approach, incorporating two methanol molecules Hydrogen-bonded to the carbonyl at position 10. The influence of the medium is more subtle in the case of anthanthrene, a hexacyclic benzenoid hydrocarbon. Unusual shifts are observed in the electronic absorption spectrum [5] when the solvent is changed from n-hexane to polyethylene. The shifts can probably be explained by dispersion interactions with crystallinic regions in the polymer material.