Proton transfer reaction of a new orthohydroxy Schiff base in protic solvents at room temperature

Ground and excited state inter- and intramolecular proton transfer reaction s of a new o-hydroxy Schiff base, 7-ethylsalicylidenebenzylamine (ESBA) hav e been investigated by means of absorption, emission and nanosecond spectro scopy in different protic solvents at room temperature and 77 K. The excite d state intramolecular proton transfer (ESIPT) is evidenced by a large Stok es shifted emission (similar to 11 000 cm(-1)) at a selected excited energy in alcoholic solvents. Spectral characteristics obtained reveal that ESBA exists in more than one structural form in most of the protic solvents, bot h in the ground and excited states. From the nanosecond measurements and qu antum yield of fluorescence we have estimated the decay rate constants, whi ch are mainly represented by nonradiative decay rates. At 77 K the fluoresc ence spectra are found to be contaminated with phosphorescence spectra in g lycerol and ethylene glycol. It is shown that the fluorescence intensity an d nature of the species present are dependent upon the excitation energy. ( C) 2000 Elsevier Science B.V. All rights reserved.