Abstract Absorption, luminescence excitation and emission spectra of nine compounds from 4, 8, 4'-trimethylpsoralen, 4, 4'-dimethylangelicin, and 1, 2, 3, 4-tetrahydrocarbazole series with various terminal substituents were studied in water and 2-propanol. Proceeding from the data obtained in the present and also some previous studies we have formulated the main rules concerning a general mechanism of changes in the fluorescence ...