Polynorbornene Copolymer with Side-Chain Iridium(III) Emitters and Carbazole Hosts: A Single Emissive Layer Material for Highly Efficient Electrophosphorescent Devices

Abstract

Vinyl addition copolymerization of norbornene monomers using a Pd(II) catalyst in combination with 1-octene chain transfer agent efficiently produces well-defined soluble polynorbornene copolymers bearing side-chain (C boolean AND N)(2)Ir(O boolean AND O) emitters (C boolean AND N = 2-(4,6-difluorophenyl)-pyridine (M-3); 2-phenyl-pyridine (M-4); 2-(benzo[b]-thiophen-2-yl)-pyridine (M-5), O boolean AND O = acetylacetonato) and 9,9 '-(1,3-phenylene)bis-9H-carbazole (mCP) or 9,9 '-(1,1 '-biphenyl)-4,4 '-diylbis-9H-carbazole (CBP) host moieties (M-1 and M-2). The catalytic system provides high-molecular-weight copolymers (M-w = 151 000-457 000 g/mol) with a controlled incorporation of monomers. All copolymers possess high thermal stability with high decomposition (T-d5 > 400 degrees C) and glass transition temperatures (T-g > 330 degrees C). Among the solution-processed devices fabricated based on a single emissive layer comprising the blue-, green-, and red-phosphorescent copolymers (PBn, PGn, and PRn, n = 1-4) with various concentrations of emitters (1.7-13.9 mol %-Ir), the devices based on PB4 (10.5 mol %-Ir), PG2 (5.3 mol %-Ir), and PR4 (13.9 mol %-Ir) display the best performances with maximum power efficiencies of 12.9, 25.6, and 3.3 lm/W and maximum external quantum efficiencies of 8.8, 13.3, and 5.1%, respectively, for each color. These results correspond to almost double the efficiencies of the corresponding doped polymer systems and are outstanding among the polymeric rivals reported thus far.