Synthesis and Photophysical Properties of π-Conjugated Polymers Incorporated with Phosphorescent Rhenium(I) Chromophores in the Backbones

A series of π-conjugated co-polymers {(P)[Re] x ( x = 0.1, 0.2, and 0.5)} incorporated with fac -(bpy)Re(I)(CO) 3 Cl (bpy = 2,2‘-bipyridine, Re = rhenium) chromophores in the backbones have been synthesized. The Re(I) chromophore contents were accurately controlled by the contents of bpy segments in (P)[bpy] x ( x = 0.1, 0.2, and 0.5) co-polymers. The structures of (P)[Re] x co-polymers were characterized by 1 H nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) analysis, and their optical and electronic properties were measured by electronic absorption, steady-state and time-resolved fluorescence, and field-induced surface photovoltaic spectroscopy (SPS). At room temperature, the characteristic metal-to-ligand charge-transfer ( 1 MLCT) absorption band and red emission of 3 MLCT from fac -(bpy)Re(I)(CO) 3 Cl chromophores can be observed. Electroluminescence (EL) devices that use (P)[Re] x co-polymers as the active layers showed enhanced red 3 MLCT emission. However, the photoluminescence (PL) and EL efficiency of (P)[Re] x co-polymers were lower, compared to those of a fac -(bpy)Re(I)(CO) 3 Cl molecularly doped polymers. The lower emission of (P)[Re] x co-polymers is conceivably related to the charge carrier separation of localized electron−hole pairs (excitions) in the sites of fac -(bpy)Re(I)(CO) 3 Cl as they became incorporated with extensive π-conjugation chains. Further studies of density functional theory (DFT) calculation and SPS provided proof of charge carrier separation in (P)[Re] x co-polymers. The efficient charge carrier separation would decrease the efficiency of PL and EL but enhance the photovoltaic efficiency, which meant a more suitable application of the types of π-conjugated polymers incorporated with transition-metal complexes in their backbones.