Study on the nanosecond transient absorption spectra of hypocrellin A.

In this paper, the nanosecond transient absorption spectra and the fluorescence spectra of Hypocrellin A(HA) are examined in solvents of varying polarity. There are three absorption bands in dilute HA solutions: Ia, IIa are defined as the triplet-triplet absorption of HA, the band IIIa is supposed to be the absorption of the solvent-separated ion pair (SSIP). In more concentrated solutions, only the absorption of SSIP was observed. The effects of solvent polarity on transient absorption spectra and fluorescence spectra of HA and the effect of oxygen on the intensities of the fluorescence of HA are discussed. Then a reasonable mechanism for the photolysis of HA is proposed.