Physico-chemical studies on some fluorescence sensors: DFT based ESIPT process.

A group of novel heterocyclic Schiff base derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. Excited state intramolecular proton transfer (ESIPT) processes in o-hydroxy Schiff base have been studied using electronic spectral studies. Experimental and FT studies support that trans enol form predominates over the cis enol form. The fluorescence of Schiff bases quenched markedly with the gradual addition of Cu(2+). DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base derivatives 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 the ground state. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analysis. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and the molecular electrostatic potential (MEP) energy surface studies evidenced the existence of intramolecular charge transfer (ICT) within the molecule.