Influence of polyhedral oligomeric silsesquioxanes (POSS) on the luminescence properties of non-conjugated copolymers based on iridium complex and carbazole units

Abstract

Non-conjugated copolymers with iridium complex and carbazole groups and polyhedral oligomeric silsesquioxane (POSS) moieties as pendant groups were synthesized by free radical copolymerization. The luminescent properties of the polymeric hybrid materials containing the carrier-transporting units (carbazole groups), phosphorescence units (iridium complex) and nano-scale particles (POSS) were studied to explore the effect of POSS on the luminescence of non-conjugated copolymer hybrid materials. The results showed that the copolymers with POSS exhibited good solubility in common organic solvents and better film-formation property. The photoluminescence decays of all copolymers in solid state were bi-exponential indicating the presence of more than one emissive species, which was attributed to intra-polymer chromophore interactions. The luminescence lifetimes of the copolymers were 0.28-1.60 μs, indicating phosphorescence emission. The luminescence properties of the copolymers were improved significantly by incorporating bulky POSS into the polymer side-chain, and the maximum quantum efficiency was found to be 52.4% for ternary copolymer PCz-Ir1.0-POSS6, which was more than six times than that of binary copolymer PCz-Ir1.0 (Φpl = 7.7%). The grafted bulky POSS can enhance the thermal stability, however, POSS had no influence on the electrochemical properties of the copolymers.