Oxadiazole containing conjugated-nonconjugated blue and blue-green light emitting copolymers

A series of segmented copolymers containing oxadiazole groups in the conjug ated main chain have been synthesized with the objective of raising the ele ctron transport ability. The present copolymers consist of alternating bloc ks of rigid chromophores containing oxadiazole units together with flexible spacer segments. The effects of chromophore substituents on the optical pr operties of the copolymers were investigated. Strong solvatochromic effects were observed, indicating intramolecular charge transfer in the excited st ates. The copolymers not only were used as blue-green electroluminescent ma terials but also were effective as electron transport/hole blocking layers in polymer light emitting diode architectures as a result of the introducti on of electron transporting unit oxadiazole. The quantum efficiency of a si ngle-layer device using PPV was greatly enhanced with the use of a thin fil m of the oxadiazole copolymer serving as an ETL layer. At 6.8 V, a brightne ss of 2400 cd/m(2) was achieved with an external quantum efficiency of 0.09 4%.