| Abstract
| - New statistical copolymers with bipolar carrier transport abilities were synthesized throughfree radical copolymerization of N-vinylcarbazole (NVK, hole-transport monomer) with eitherof two substituted styrenes containing oxadiazole groups, which serve as electron transportmonomers: 2-phenyl-5-{4-[(4-vinylphenyl)methoxy]phenyl}-1,3,4-oxadiazole, PVO, and 2-(4-tert-butylphenyl)-5-{4-[(4-vinylphenyl)methoxy]phenyl}-1,3,4-oxadiazole, BVO. In all cases,the charge transport moieties exist in side groups, and carrier transport proceeds by hopping.Copolymerization yields homogeneous statistical copolymers of widely variable compositionand thus tunable carrier transport properties; the copolymers are transparent in the visibleregion and form good films. Compared with systems where the oxadiazole units areincorporated by simply blending a small-molecule oxadiazole into poly(N-vinylcarbazole),the glass transition temperatures of these copolymers are high, and there is no possibilityfor the oxadiazole units to phase-separate through recrystallization. The glass transitiontemperatures for the copolymers show positive deviations from a harmonic mixing rule,suggesting some interaction between the NVK and BVO residues; however, blends of thehomopolymers show limited miscibility at best, indicating that copolymerization is essentialto produce a homogeneous material. Incorporating the oxadiazole units reduces the holetransport ability of these copolymers somewhat relative to NVK homopolymer, but single-layer dye-doped devices emitting blue, green, and orange light fabricated from thesecopolymers all showed good efficiency.
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