HYDROGEN-BONDING AND PROTON-TRANSFER INTERACTIONS BETWEEN HARMANE ANDTRIFLUOROETHANOL IN THE GROUND AND EXCITED SINGLET-STATES

A study of the hydrogen-bonding and proton transfer reactions of the g round and excited states of harmane (1-methyl-9H-pyrido/3,4-b/indole) and its N-9-methyl derivative with 2,2,2-trifluoroethanol in cyclohexa ne is reported. Spectral measurements (UV-visible, Fourier transform I R, steady-state and time-resolved fluorescence) show the formation of fluorescent ground-state hydrogen-bonded complexes. The results have b een interpreted assuming a tautomeric equilibrium between a 1:1 hydrog en-bonded complex and its 1:2 proton transfer tautomer (hydrogen-bondi ng ion pair). Upon excitation to its singlet excited state, the proton transfer tautomer of harmane reacts with an additional 2,2,2-trifluor oethanol molecule to give a zwitterionic exciplex, which fluoresces at longer wavelength.