Fluorescence and phosphorescence of aromatic β-carbolines on dispersed solid phase at 77 K and room temperatures

Abstract The fluorescence and phosphorescence spectra of the alkaloids norharman, harman and harmine and their hydrochlorides were studied at 77 K. The spectra of the basic molecules dissolved in ether-isopentane-ethanol show a well-resolved vibrational structure, whereas the spectra of hydrochlorides dissolved in an H 2 SO 4 -ethanol mixture are poorly resolved and in the case of fluorescence spectra some blue shift is noticed for these acid molecules. Fluorescence and phosphorescence spectra have also been recorded at room temperature for acid molecules adsorbed on cellulose, but they have a poorer intensity and worse resolution than those recorded at 77 K. The p K a values for the acid-base equilibrium on the first excited triplet T 1 were derived using the Forster-Weller relation. They were found to lie near the values corresponding to the first excited singlet S 1 rather than the values found for the ground state S 0 .