Physicochemical studies of chemosensor imidazole derivatives: DFT based ESIPT process

A series of substituted imidazoles have been synthesized in very good yield under a solvent free condition using molecular iodine as the catalyst. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives have been performed and discussed. DFT analysis about HOMO, HOMO−1, LUMO and LUMO+1 has been carried out and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state that is shown by PES calculation. The molecular electrostatic potential surface (MEP) has also been employed to show the higher electron density at N(3) nitrogen. Fluorescence enhancement has been found in the presence of transition metal ions and this may result from the suppression of radiationless transitions from the n–π* state in the chemosensors.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Under solvent free condition using molecular iodine as the catalyst. ► The enhancement of fluorescence during exposure to metal ions. ► HOMO–LUMO – probable charge transfer (CD) taking place inside the chromophore. ► Formation of the keto-isomer III due to ESIPT. ► Competition of intra and intermolecular hydrogen bonding in binary solvents.