Carbazolevinylene-based polymers and model compounds with oxadiazole and triphenylamine segments: Synthesis, photophysics, and electroluminescence
2008
Vellis, Panagiotis D. | Mikroyannidis, John A. | Cho, Min Ju | Choi, Dong Hoon
Two new soluble alternating carbazolevinylene-based polymers POXD and PTPA as well as the corresponding model compounds MOXD and MTPA were synthesized by Heck coupling. POXD and MOXD contained 2,5-diphenyloxadiazole segments, while PTPA and MTPA contained triphenylamine segments. All samples displayed high thermal stability. The polymers had higher glass transition temperature (Tg) than their corresponding model compounds. The samples showed absorption maximum at 364-403 nm with optical band gap of 2.62-2.82 eV. They emitted blue-green light with photoluminescence (PL) emission maximum at 450-501 nm and PL quantum yields in THF solution of 0.15-0.36. The absorption and the PL emission maxima of PTPA and MTPA were blue-shifted as compared to those of POXD and MOXD. The electroluminescence (EL) spectra of multilayered devices made using four materials exhibited bluish green emissions, which is well consistent with PL spectra. The EL devices made using poly(vinyl carbazole) doped with MOXD and MTPA as emitting materials showed luminances of 12.1 and 4.8 cd m⁻². POXD and PTPA exhibited 25.4, and 96.3 cd m⁻², respectively. The polymer containing the corresponding molecules in the repeating group showed much higher device performances. Additionally, POXD and MOXD exhibited better stability of external quantum efficiency (EQE) and luminous efficiency with current density resulting from enhancing the electron transporting properties.
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