Photoreactive hole-transporting polymer bearing oxetane moieties and its application to green polymer light-emitting diodes

A new hole-transporting polymer was prepared by the copolymerization of 9-(4-vinyl-benzyl)-9H-carbazole and 3-methyl-3-(4-vinyl-benzyloxymethyl)-oxetane in the presence of α,α′-azobisisobutyronitrile (AIBN). The latter contains an oxetane unit that is cationically photopolymerizable. It was characterized by NMR, GPC, IR spectroscopy, TGA, and differential scanning calorimetry (DSC). Multilayer polymer light-emitting diodes (PLEDs) were fabricated layer by layer by using the spin-coating method with an organic solution of a photoreactive copolymer. Organic soluble poly[2-(carbazol-9-yl)-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (CzEh-PPV) that carries hole-transporting carbazole pendants was also synthesized and employed as a green-emitting material in PLEDs. After UV illumination for photoreaction in the new photoreactive oxetane-based copolymer (VCz-Ox), we could spin coat the CzEh-PPV solution for the next layer. The hole-transport capability of the copolymer was evaluated in multilayer PLEDs that were fabricated to test the device performances.