Electroluminescent main-chain copolymers containing phosphorescent benzimidazole-based iridium complexes as copolymerization backbone units or dopants

Abstract

A series of novel electroluminescent main-chain copolymers containing fluorene-1,4-bis(9-octyl-9H-carbarzol-3yl)-2,5-dioctyloxy-benzene (BCB) segments and phosphorescent benzimidazole-based iridium (Ir) complexes in the backbones were synthesized by Suzuki coupling reaction. The relative intensity of phosphorescence and fluorescence were affected by the energy transfer and back transfer efficiencies between the polymer backbones and the iridium units as evidenced by solid state PL and EL spectra. PLED devices with a configuration of TTO/PEDOT: PSS (70 nm)/Ir-copolymers (P3-P10) or Ir-doped copolymers (P1-P2 doped with Ir-complex 4) (60-80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm) were fabricated, where electroluminescence (EL) efficiencies depended on the chemical constituents and the triplet energies of the copolymers. PLED devices based on Ir-containing copolymer P8 or copolymer P2 doped with 5 mol% Ir-complex 4 exhibited white-light emissions with EL properties of eta(ext,max) = 0.93%, eta(c,max) = 1.88 cd A(-1), and L(max) = 1960 cd m(-2) from the former (P8), and eta(ext,max) = 4.09%, eta(c,max) = 10.94 cd A(-1), and L(max) = 4870 cd m(-2) from the latter (P2 doped with Ir-complex 4), respectively. The CIE coordinates, color-rendering index (CRI) and correlated color temperature (CCT) of the two PLED devices were (0.33, 0.30) at 13 V, 74 and 5966 K for the former, and (0.35, 0.32) at 15 V, 82 and 6147 K for the latter, respectively.