Abstract
The emission spectra and the fluorescence quantum yields of psoralens were measured in various solvents. We found that these compounds show a large Stokes shift, which can be explained in terms of intermolecular charge transfer interaction between a solute molecule and a solvent molecule in an excited singlet state. Psoralens have a larger fluorescence quantum yield in hydroxylic solvents than in non-hydroxylic solvents. These were in the following order : TMP≈5-MOP>PS≈8-MOP≈8-iso-AOP. We postulate that the fluorescence quantum yield is increased by the hydrogen bonding between a solute molecule and a solvent molecule in an excited singlet state. In addition, the fluorescence efficiency was enhanced by the presence of an electron-donating substituent group. The peak wavelengths of the phosphorescence spectra were little affected by the different solvents.
