The solvent effect on the excited-state proton transfer of lumichrome

The acetic acid (AA)-catalysed tautomerism of lumichrome (Lc) was investigated in 1,2-dichloroethane, acetonitrile and pure AA. The interactions between Lc and AA were studied by means of UV-Vis and fluorescence spectroscopy. The results suggest the formation of 1:1 Lc–AA hydrogen-bonded complexes in the ground state of Lc. The apparent equilibrium constants were one order of magnitude higher in 1,2-dichloroethane than in acetonitrile, indicating a solvent effect on the ground-state interactions. The dynamics of exited-state processes were studied using time-resolved methods. The results show that the mechanism of tautomerism depends on the solvent.