Excited state intramolecular proton transfer in salicylidine -3,4,7-methyl amine: Spectroscopic and theoretical investigations

Abstract

A new <i>ortho-</i>hydroxy<i> </i>Schiff base, salicylidine-3,4,7-methylamine (SMA) has been synthesized . Investigation has been done on the excited state intramolecular proton transfer (ESIPT) process, employing absorption, emission and nanosecond spectroscopy in some non-polar and weakly polar solvents at room temperature and at 77K. The ESIPT is evidenced by a large Stokes shifted emission (~10,700 cm^-1) both at room temperature and at 77K. The keto tautomer is found to be the predominant species in the excited state at 77K. From nanosecond measurements and quantum yields of fluorescence, we have estimated the decay rates of proton transfer reaction. Theoretically determined energetics of the ground and excited state proton transfer in SMA at AM1 level of approximation, predict that the ground singlet proton transfer path would have considerable barrier, while the barrier height should be much lower both on the corresponding excited singlet and triplet surfaces.