Benzimidazole based Ir(III) picolinate complexes as emitting materials and the fluorescent behavior of benzimidazole bound to Mn-TiO2@ZnO core/shell nanospheres

Photophysical and electroluminescent studies of cyclometalated heteroleptic iridium(III) complexes have been carried out. The strongly allowed phosphorescence in these picolinate complexes is the result of significant spin-orbit coupling of the iridium center. The lowest energy of these picolinate complexes corresponds to a mixture of metal to ligand charge transfer (MLCT) and π-π* states. Weak bands located at longer wavelength are due to the 1MLCT → S0 and 3MLCT → S0 transitions of iridium complexes. Devices show better performance in terms of brightness and moderate power and current efficiencies. Absorption, fluorescence and lifetime spectral studies have been made to probe the interaction of 2-(4-trifluoromethylphenyl)-1-phenyl1H-benzo[d]imidazole (TFMPPB) with sol-gel synthesised Mn-doped TiO2@ZnO core/shell, pristine ZnO and Mn-doped TiO2 nanoparticles. The emission of TFMPPB is enhanced by Mn-doped TiO2@ZnO core/shell, pristine ZnO and Mn-doped TiO2 nanoparticles which are likely due to lowering of LUMO and HOMO levels of the benzimidazole. Electron injection from photoexcited TFMPPB to the Mn-TiO2@ZnO CB(S* → S++e-CB) is likely to the reason for the fluorescence enhancement.