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The spectral difference in fluorescence emitted from the forms (I), ( 11) and (III) has been used to study proton transfer reactions of electronically excited molecules : * * *o 0 (I) (10 (111) A H + B + A H . . . B-tA . . . HE3 by fluorescence measurements.With intermolecular hydrogen bonds, pronounced effects of solvent and of temperature have been observed which indicate that in this case proton transfer is strongly facilitated by an increase in polarity of the surrounding medium. In polar solvents considerable changes in solvent orientation are required and can become rate-determining, particularly at low temperatures. With intramolecular proton transfer equilibria the solvent effect is weaker and in the opposite direction. This is attributed to compensation by intramolecular electron migration of the dipole moment of form (111). An upper limit of 0.12 kcal/mole has been obtained for the activation energy of the intramolecular proton transfer.

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