An intramolecular charge transfer fluorescent probe: synthesis, structure and selective fluorescent sensing of Cu+2

A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone, aromatic aldehyde and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, good yield and easy workup make this protocol practically and economically attractive and characterized by NMR spectra, X-ray, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dpip and dptip) have been studied using emission spectroscopy and it was detected that the two distinct ground state rotamers are responsible for the normal and the tautomer emissions. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives were performed and discussed. DFT analysis about HOMO, HOMO-1, LUMO and LUMO + 1 were carried out 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.