DFT based ESIPT process of luminescent chemosensor: Taft and Catalan solvatochromism

Amino acid containing o-hydroxy Schiff base derivative was synthesized and an excited state intramolecular proton transfer (ESIPT) process in o-hydroxy Schiff base (HBMBA) has been studied using solution spectral studies. It was detected that the two distinct ground state isomers I and II are responsible for the emission. By comparing the emission wavelength in hydrocarbon solvent, it was predicted that the trans enol form predominates over the cis enol form. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base derivative were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than in the ground state. The fluorescence of HBMBA quenched with the gradual addition of Cu(2+). Therefore the prepared Schiff base HBMBA can be used as a new fluorescent sensor to detect the quantity of Cu(2+) ions in any sample solution depending on the relative intensity change. Measurements of absorption solvatochromism have been interpreted with Marcus and Reichardt-Dimroth solvent functions to estimate the transition dipoles. Good correlation exists between absorption as well as fluorescence wavenumbers obtained by the multi-component linear regression employing the Taft and Catalan solvent parameters with the experimental values.