Polynorbornene copolymer with side-chain triarylborane and iridium(III) groups: An emissive layer material with electron transporting properties for PhOLEDs

Vinyl-type polynorbornene copolymers (P1-P3) containing side-chain triarylborane and iridium moieties were prepared by palladium(II) catalyzed copolymerization of norbornene monomers bearing triarylborane (Mes(2)BPh, M1) and an iridium emitter ((ppy)(2)Ir(acac), ppy = 2-phenyl-pyridinato-C-2,N; acac = acetylacetonato, M2). Copolymerization led to facile incorporation of the comonomers in a controlled manner depending on the feed ratio of the comonomers (4.0 mol%-Ir in P1; 6.7 mol%-Ir in P2; 12.4 mol%-Ir in P3). While solution PL spectra of the copolymers exhibited partial intra-chain energy transfer from the borane moiety to iridium, complete energy transfer occurred in the rigid matrix, such as at 77 K and in the film state. The LUMO level of the borane moiety (M1) was estimated to be 2.4 eV, which is lower than that of M2 and poly(N-vinylcarbazole) (PVK) (ca. 2.2 eV for both). Solution processed PhOLEDs (D1-D3) incorporating P1-P3 as an emissive material in the PVK host displayed good performance in the low current density region, but D1-D3 suffered severe efficiency roll-off with increasing current densities. Comparable performance of 02 with the device (D4) based on P2 emitter and PVK:PBD (2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) host suggested that a borane moiety in the emissive polymer chain plays an actual role in facilitating electron transport in the emissive layer. (C) 2015 Elsevier Ltd. All rights reserved.