Potential fluorescent chemosensor based on L-tryptophan derivative: DFT based ESIPT process

The spectroscopic properties of (E)-2-(2-hydroxybenzylideneamino)-3-(1H-indol-3-yl) propanoic acid (HBDIPPA) has been studied in a series of different solvents. An excited state intramolecular proton transfer (ESIPT) process in hydroxy Schiff base has been studied using emission spectroscopy. DFT calculations on energy, HOMO–LUMO energies, MEP, dipole moment, charge distribution of the Schiff base derivative have been performed and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state is shown by PES calculation. Positive values of laplacian ▿2ρ(rc) (2.81) and electron density ρ(rc) (0.22) are indicative of hydrogen bonds interactions. Absorption as well as fluorescence wavenumbers are correlated with Marcus and Reichardt–Dimroth solvent functions and also with Taft and Catalan solvent parameters. Schiff base HBDIPPA can be used as a new fluorescent sensor.

Figure optionsDownload as PowerPoint slideHighlights
► The quenching of fluorescence was observed in the presence of copper metal ion.
► ESIPT process plays important role.
► Competition of intra and intermolecular hydrogen bonding in binary solvents such as dioxane and water.
► Positive values of laplacian ▿2ρ(rc) (2.81) and electron density ρ(rc) (0.22) are indicative of hydrogen bonds interactions.
► PES diagram, MEP and electronic properties studied using Gaussian-03.