[Relationship between absorption and fluorescence excitation spectra of psoralens and coumarins and their concentration].

The shape of absorption spectra is changed and their maxima are red shifted with an increase of furocoumarin (psoralen, 8-methoxypsoralen and angelicin) concentration. Fluorescence excitation spectra of psoralen, 7-methoxycoumarin and 7-hydroxy-4-methylocumarin do not depend on the concentration in solutions. They are similar or coincident with absorption spectra of the most concentrated solutions. One may conclude the existence of different forms of furocoumarin and coumarin aggregates in solution. From the coincidence or similarity of fluorescence excitation spectra and absorption spectra in the most concentrated solutions it may be proposed that only the aggregated forms of psoralens and coumarins (the dimers or associates of higher order) are able to emit fluorescence.