Synthesis, characterization and photophysical properties of rhenium(I)-containing polyfluorene-based copolymers

A new series of π-conjugated [2,7-(9,9′-dihexylfluorene)-co-alt-5,5′-(2,2′-bipyridine)] (fluorene-co-bpy) copolymers containing fac-(bpy)Re(I)(CO)3Cl (bpy=2,2′-bipyridine, Re=rhenium) chromophores were synthesized and well characterized. The chelating copolymers showed characteristic MLCT absorption and emission at room temperature. Bonded Re complexes harvested excited energy efficiently through intra- and intermolecular energy from polymer backbone to Re complexes; however, both photoluminescence (PL) and electroluminescence (EL) efficiencies were unexpectedly lower. Such lower luminescent efficiency was conceivably related to charge carrier separation of localized electron-hole pairs (excitons) in fac-(bpy)Re(I)(CO)3Cl, which was induced by extensive π-conjugation. Further studies of density functional theory (DFT) calculation and surface photovoltaic spectra (SPS) afford proofs of charge carrier separation in fac-(bpy)Re(I)(CO)3Cl chelating polymers. The efficient charge carrier separation will decrease the efficiency of PL and EL but enhance the photovoltaic efficiency.