Monochromic red-emitting nonconjugated copolymers containing double-carrier-trapping phosphine oxide Eu³⁺ segments: Toward bright and efficient electroluminescence

Two metallopolymers P1 and P2 were prepared by using a novel polymerizable Eu³⁺ complex Eu(TTA)₃VBADPO (EuMA) (TTA = 2-thenoyltrifluoroacetonate) and vinylcarbazole as the monomers in the ratios of 1:99 and 3:97, respectively, in which VBADPO is 2-(diphenylphosphoryl)-N-(2- (diphenylphosphoryl)-4-methoxyphenyl)-4-methoxy-N-(4-vinylbenzyl)aniline as a polymerizable aryl phosphine oxide ligand with a bipolar structure. The copolymers exhibit the excellent optical properties with photoluminescence quantum yield more than 60% in film. Both Gaussian simulation and electrochemical analysis indicated that the Eu³⁺-complexed segments form double-carrier traps (Eu-trap) in the copolymers with depth of 0.1 eV for the hole and 0.7 eV for the electron. The single-layer spin-coated devices of P1 and P2 realized the pure red emissions from Eu³⁺ ions. The biggest luminance of 149.1 cd m^-2 was achieved, which is the highest among those of electroluminescent (EL) Eu³⁺-containing copolymers reported so far. The unusual efficiency stability proves the limited concentration quenching and T-T annihilation in P1 and P2 due to the uniform dispersion of emissive Eu³⁺ chelate moieties in the host matrix. With the high brightness and very stable efficiencies, P1 is favorable among the high-performance Eu³⁺-containing copolymers. It is also proved that the formation of carrier-traps in the copolymers is effective to improve EL performances.