مشخصات پژوهش

In this work, we report photophysical studies of two Schiff bases, namely ethyl N-(5-bromosalicylidene)glycinate (1) and ethyl N-(5-nitrosalicylidene)glycinate (2). Both dyes were synthesized from the ethyl ester of glycine hydrochloride and corresponding salicyladehyde derivatives in the presence of trimethylamine using a newly developed sonochemical approach in the ethanol medium, which allowed to completely avoid using benzene as a reaction medium. The UV–vis spectrum of 2 in CH2Cl2 is described by the presence of the corresponding absorption band in the visible region, characteristic for the cis-keto-enamine tautomer as opposed to the enol-imine form prevalent in the spectrum of 1 in the same solvent. Both 1 and 2 found to be inert to the presence of NEt3, regardless of its concentration, in CH2Cl2. During the titration of a solution of 1 in CH2Cl2 by CH3SO3H a new band in the visible region appears and gradually increases, which is due to a specific interaction of 1 with CH3SO3H, where the solute molecules are not protonated but, contrarily, the keto-enamine tautomer is formed. This also results in an emission band at about 475 nm, which is gradually increased with increasing of the acid concentration. The emission band arises from the emission of the keto-enamine tautomer of 1, exhibiting, most likely, two conformers. Contrarily, gradual addition of CH3SO3H into a solution of 2 in CH2Cl2 decreases an intensity of the band in the visible region, characteristic for the cis-keto-enamine tautomer, until it completely disappears. While the bands at 239 and 318 nm decrease upon addition of CH3SO3H, a shoulder at about 260 nm increases up to 2 eqv. of the added CH3SO3H, followed by decreasisng until it completely disappears. This is due to protonation of the imine nitrogen atom, followed by the protonation of the NO2 group. Titration of a solution of 2 in CH2Cl2 by CH3SO3H increases intensity of the emission band up to about 2 eqv. of the added acid, followed by decr