Physico-chemical studies of new luminescent chemosensor for Cu2+

The spectroscopic properties of (E)-2-(2-hydroxybenzylideneamino)-3-phenylpropanoic acid (HBDPPA) has been studied in a series of different solvents. As revealed by absorbance, and emission results, the molecule undergoes fast excited-state intramolecular proton transfer (ESIPT) to yield emission of the corresponding tautomeric species. A large energy barrier for interconversion of the keto-enol rotamers in the ground and excited state have been predicted on the basis of DFT calculations and also supported by HOMO–LUMO energies, PES calculation, NLO and NBO analysis. Hyperpolarizability and octupolar and dipolar components ratio confirmed that HBDPPA can be used as optoelectronic materials. The ground state equilibrium and ESIPT process of HBDPPA are essentially unaffected by the nature of the solvent. 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. The prepared Schiff base HBDPPA can be used as a new fluorescent sensor to detect the quantity of Cu2+ ion in any sample solution depending on the relative intensity change.

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► The quenching of fluorescence was observed in the presence of copper metal ion.
► ESIPT process plays main role.
► Competition of intra and intermolecular hydrogen bonding in binary solvents.
► NBO analysis revealed that the n(N1) → π∗ O(30)–H(31) interaction gives the strongest stabilization to the system.
► PES diagram, MEP and electronic properties studied using Gaussian-03.