Abstract
Quantitative singlet absorption spectra dependent on solvent, temperature, and concentration are shown. The bands observed in the visible and UV region are assigned to 3 π → π*-electron transfers. Measurements at different acidities showed that the pheophytin molecule can be present in 3 prototropic forms; as a base, a mono- or a divalent cation. In polar solvents of concentrations >10-4 M dimerization occurred. Larger clusters were formed in non-polar solvents at concentrations <10-4 Μ and at temperatures below ca. 200 °K. The quantitative triplet (T) -absorption spectra for pheophytin a and b are also reported: the longest wavelength T-T-band is expected in the region 5000-8000 cm-1. The relaxation times and quantum yields of triplet formation are given; simple first order kinetics were found to fit the decay curves.
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