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

Abstract

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%.

Synthesis and electroluminescent property of poly(p-phenylenevinylene)s bearing triarylamine pendants

“…There have been several reports on the improvement of p-conjugated polymers such as PPV and polyfluorene by introducing hole-transporting and/or electron-transporting groups to realize highly efficient electroluminescence [9][10][11][12][13][14][15][16][17]. For example, Jin et al reported PPV-based copolymers containing an oxadiazole group with an electron injecting and transporting ability [9].…”

Luminescent copoly(aryl ether)s consisting of alternate oxadiazole and 1,4‐distyrylbenzene derivatives: Synthesis and characterization

“…The emitting wavelength is mainly determined by the effective π‐conjugation length in the excited state and by nonresonant or resonant coupling to surrounding electronic oscillators 7. Furthermore, block copolymers with isolated alternating segments have been synthesized to control the emitting wavelength 8–11. These copolymers provide efficient exciton confinement because of the microphase‐separated domain structure, and by the appropriate selection of chromophores, they can provide emissions at any selected portion of the spectrum 12…”

Organic Light‐Emitting Diodes

“…One way, used by Hay and Klavetter [200] and by Karasz and coworkers [201][202][203] proceeds by the linkage of a functional phenylene vinylene segment (commonly 3 units) with flexible spacers. These copolymers have been prepared by Wittig or Knoevenagel polycondensations and emit in the blue region [200][201][202][203], but the emission spectra are broadened due to the dilution effect of the chromophores by the insulating spacers. Green and yellow emissions have also been produced by copolymers of cyano-containing PPV-based chromophores and a flexible spacer as shown for the yellow light-emitting polymer XVII [201].…”