Site selection spectroscopy and photochemical hole-burning of hypericin

High-resolution fluorescence and excitation spectra of hypericin in ethanol and in polyvinylbutiral are reported. Persistent spectral hole-burning is highly efficient in ethanol with a quantum yield Φhb∼1.1 × 10−2. Evidence is shown for a photoproduct located at about 200 cm−1 below the burnt hole. Possible photochemical reactions are discussed.