The ground and singlet excited-state hydrogen-bonding interactions of N-methylindole with trifluoroethanol in n-hexane: a model to explain the anomalous fluorescence of indole in polar protic solvents

UV–Vis and FTIR absorption, steady-state and time-resolved fluorescence studies on the hydrogen-bonding interactions of N-methylindole, 1MI, with trifluoroethanol, TFE, in n-hexane, reveal the formation of a ground state fluorescent hydrogen bonded complex, HBC, and a red-shifted and weakly fluorescent exciplex, PTC. The proposed mechanism for the exciplex formation can serve as a model to explain the anomalous large Stokes shift and quenching of indole fluorescence in highly polar protic solvents.