A detailed examination of the absorption spectra, the polarized phosphorescence spectra, and the polarized excitation spectra of xanthone (C2v symmetry) in polar and nonpolar media has been carried out at 77°K. Five electronic transitions in the absorption region between 27,000 and 44,000 cm-1 have been assigned. They are, in order of increasing energy: 1A2 (n,π*) ← 1A1, 1A1 (π,π*) ← 1A1, 1B2 (π,π*) ← 1A1, 1A1 (CT) ← 1A1 (tentative), and 1A1 (π,π*) ← 1A1 (tentative). Lifetime and polarization measurements, as well as vibrational features, indicate that the configuration of the lowest triplet state is nπ* in the 3-methylpentane (3-MP) solvent but ππ* in polar solvents. In both EPA and 3-MP the phosphorescence kinetics of xanthone are nonexponential. Time-delayed phosphorescence and excitation spectra show that the mixed kinetics in 3-MP are due to a small amount of the same phosphorescent species (3π,π*) which is dominant in EPA. Moreover, polarization spectra indicate that a small amount of the phosphorescent species (3n,π*) which is dominant in 3-MP produces the deviation from the exponential decay in EPA. This phenomenon is suggested to arise mainly from two types of solute-solvent cage configurations.
ASJC Scopus subject areas
- Colloid and Surface Chemistry