Dual Emissions of Salicylidene-5-chloroaminepyridine Due to Excited State Intramolecular Proton Transfer: Dynamic Photophysical and Theoretical Studies

Abstract

In this study, the photophysical properties of N-salycilidene-5-chloroaminopyridine were evaluated. This molecule presented dual emission from the keto* and enol* species, depending on the solvent used (DMSO or methanol in the absence and presence of trifluoroacetic acid). This molecule was synthesized through a dehydration reaction of salicylaldehyde under sonication and characterized using FTIR, cyclic voltammetry, mass spectrometry, and single-crystal X-ray diffraction, yielding the molecular structure. Theoretical calculations were performed under the DFT framework and its time-dependent counterpart. Our results suggest the occurrence of excited state proton transfer, ESIPT, in the aprotic solvent, leading to a keto*–enol* balance, which is confirmed by the emission bands observed at 425 and 545 nm, respectively. However, in a protic environment (methanol or DMSO with trifluoroacetic acid), only the enol form is emissive due to the hydrogen bonding between the iminic group and the solvent. Molecules with double emissions are potentially useful for white light emitting diodes.