Contrasting emission behavior of phenanthroimidazole with rutile and anatase TiO2 nanoparticles

A new type of emitter 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole has been designed and synthesized. Absorption, emission, FT-IR and lifetime spectroscopies have been used to investigate the binding of phenanthroimidazole molecule with the nanoparticulate anatase and rutile TiO2. The fluorescence emission of the phenanthroimidazole is quenched effectively by anatase particulate TiO2 due to charge injection from the excited singlet state of phenanthroimidazole to the conduction band of the TiO2 nanocrystals. Surprisingly, nanocrystalline rutile enhances the fluorescence. This is because of lowering of LUMO and HOMO energy levels of phenanthroimidazole molecule. Electron injection from photoexcited phenanthroimidazole to conduction band of rutile TiO2 image is likely to enhance the fluorescence. The HOMO and LUMO energies of phenanthroimidazole are deduced from cyclic voltammetric results. To support the experimental results DFT calculation has been made for Gaussian-03.