ELSEVIER Synthetic Metals 84 (1997) 437-438 A blue light emitting copolymer with charge transporting and photo-crosslinkable functional units Xiao-Chang Li,a Tuck-Mun Yong, a Johannes Griiner,c Andrew B. H~lmes,~$~* Stephen C. Moratti,b Franc0 Cacialli,c and Richard H. FriendC aDepartment of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 IEW, U.K. bMelville Laboratory for Polymer Synthesis, University of Cambridge, Pembroke Street, Cambridge CB2 3R.4, U.K. =Department of Physics, University of Cambridge, Madingley Road, Cambridge CB3 OHE, U.K. Abstract The synthesis of a new poly(methacrylate) copolymer bearing an efficient blue light emitting chromophore, a charge transporting aromatic oxadiazole and a UV-sensitive crosslinkable unit is reported. The statistical copolymer was synthesized via a multi-step route and has been characterised by NMR, FT-IR, and DSC. The copolymer has excellent solution processibility and exhibits strong luminescence. Upon cross-linking via UV-treatment, the copolymer becomes insoluble, while gaining both mechanical strength and thermal stability without loss of luminescence. The structure and properties of this novel copolymer and its application in light emitting devices are discussed. Keywords: Copoly(methacrylate); Charge transport; Crosslinking; Photoluminescence; Electroluminescence; Blue LED; 1. Introduction The emission colour of poly(phenylene vinylene) has been successfully tuned from green to red by introduction of suitable substituents [l]. Although PPV with blue-shifted has been obtained by controlling the conversion of the precursor, or by using meta-linked phenylene [Z], achievement of a true blue colour requires conjugation-breaking spacers or even a discrete blue chromophore. Examples toward this strategy include main chain polymers with phenylenevinylene chromophores [3,4], and side chain polymers such as poly(norbornene) [S] and polystyrene [6] with pendant phenylenevinylene chromophores. As part of ongoing efforts to obtain blue light emitting polymers (LEPs) with improved charge-transporting properties (and hence better device characteristics), we have recently reported a poly(methacrylate) bearing a pendant distyrylbenzene and an aromatic oxadiazole [7]. We now report a tri-functional poly(methacrylate) that bears blue-light emitting distyryl benzene, electron transporting aromatic oxadiazole and photo- crosslinkable cinnamoyl groups (Scheme). 2. Results and discussion The copolymerisation reaction was typically carried out under nitrogen using 0.3 % AIBN (mole/mole) as radical initiator in degassed THF. The composition of the copolymer can be readily varied by simply changing the ratio of the starting monomers, so as to adjust the charge transporting capability, the extent of crosslinking and even the wavelength of emission. For convenience, an equal weight of 1,2 and 3 has been used for the copolymerisation, leading to a * Ccmesponding author. 0379-6779/971$17.00 0 1997 Elsevier Science S.A. All rights reserved PII 80379-6779(96)03975-6 copolymer with p = 0.28, q = 0.53 and r = 0.19 (Scheme). The composition as well as the structure of the copolymer has AlBNrmF 60 ‘C/ 6 h 62% UV Irradiation 5-40 min. Crosslinked 4 Scheme. Synthesis of a multi-functional blue LEP been confirmed both by microanalysis and by lH NMR spectroscopy. Yellow powdery copolymer 4 was obtained in good yield after purification by several precipitations from methanol. The copolymer 4 is soluble in chlorinated solvents,