Oxadiazole Containing Conjugated−Nonconjugated Blue and Blue-Green Light Emitting Copolymers

A series of segmented copolymers containing oxadiazole groups in the conjugated main chain have been synthesized with the objective of raising the electron transport ability. The present copolymers consist of alternating blocks of rigid chromophores containing oxadiazole units together with flexible spacer segments. The effects of chromophore substituents on the optical properties of the copolymers were investigated. Strong solvatochromic effects were observed, indicating intramolecular charge transfer in the excited states. The copolymers not only were used as blue-green electroluminescent materials but also were effective as electron transport/hole blocking layers in polymer light emitting diode architectures as a result of the introduction of electron transporting unit oxadiazole. The quantum efficiency of a single-layer device using PPV was greatly enhanced with the use of a thin film of the oxadiazole copolymer serving as an ETL layer. At 6.8 V, a brightness of 2400 cd/m 2 was achieved with an external quantum efficiency of 0.094%.