8-methoxy-psoralen (8MOP), was studied with UV absorption spectroscopy at room temperature and steady state and time-resolved emission spectroscopic techniques at 77 K. UV absorption spectra were interpreted with the aid of molecular orbital calculations using AM1/MOPAC-93 and HAM/3-CI methods. There exist different species depending upon environments. Each one of them displays quite distinct photophysical properties. The following species were found: in methylcyclohexane, the molecular aggregation and monomer were found; in ethanol, hydrogen bonding complex (HBC) between 8MOP and ethanol; in ethanol plus 3,3,3,1,1,1-hexafluoroisopropanol, a strong hydrogen bonding complex (SHBC) in buffer solution (pH = 7.0, I = 0.1 M), a strong hydrophobic aggregation (SHA) and in buffer solution (pH = 8.5. I = 0.25 M) monomer from SHA. We used the anionic, cationic and neutral micellar solutions to mimic a biological membrane, The species of 8MOP in anionic, cationic and neutral micelles solution is the monomer that penetrates into the interior of micelle staying anchored to its hydrophobic region forming SHBC. (C) 2002 Published by Elsevier Science B.V.9741732237249