Several poly(N‐phenyl‐2,7‐carbazole)s that have dialkoxy groups at the m‐ and p‐positions (PmpCzDC, PmpPhDC, PmpCBiDC, PmpEHC), a silyl group at the p‐position (PpPhDSiC), and a diphenylamino group (PmPhDAC, PmEHAC) at the m‐position of the N‐phenyl portion are synthesized, and their optical properties are characterized. These polymers have been used as emitting layer materials of organic light‐emitting diode (OLED) devices that have a configuration of ITO/PEDOT(PSS)/polymer/CsF/Al. The OLED devices embedded with PmpCzDC, PmpPhDC, and PmpEHC show intense luminance of about 15 000 cd · m−2 with efficiencies of about 1 cd · A−1, while the devices embedded with PpPhDSiC, PmPhDAC, and PmEHAC show less luminance but retain the color purity of blue emission under a wide range of applied voltages.

Carbazole and fluorene‐based random and alternating copolycondensates were synthesized to develop high‐performance blue light‐emitting polymers by improving electron injection ability of poly(N‐aryl‐2,7‐carbazole)s that showed intense blue electroluminescence (EL) with good hole‐injection and ‐transport ability. These copolycondensates absorbed light energy at about λmax = 390 nm in CHCl3 and 400 nm in film state, and fluoresced at about λmax = 417 nm in CHCl3 and 430 nm in the thin film state. Energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of them were about 2.9 eV, and the energy levels of LUMO situated lower than that of corresponding polycarbazole. Polymer light‐emitting diode devices having configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)/polymer/CsF/Al using the copolycondensates, poly(N‐arylcarbazole‐2,7‐diyl), and poly(9,9‐dialkylfluorene‐2,7‐diyl), emitted bluish EL at operating voltages lower than 7 V. The device embedded the random copolycondensate showed notably higher performance with maximum luminance of 31,200 cd m−2 at 11.0 V, and the current efficiencies observed under operating voltages lower than 7 V were higher than those of the other devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Demonstration of highly efficient organic light-emitting diodes (OLEDs) is becoming commonplace; however, there have been few reports on hole-transporting materials (HTMs) designed for highly efficient and stable green OLEDs. Here, operationally stable HTMs with high triplet energy were synthesized by incorporating dibenzothiophene and dibenzofuran into hole-transporting amino groups. The triplet energy of the amine derivative with dibenzothiophene was increased from 2.35 to 2.56 eV by introducing o,o′-quaterphenyl without impairing the stability. Since the largest triplet energy of the synthesized HTMs is 2.59 eV, the triplet excitons of green phosphorescent emitters and thermally activated delayed fluorescence (TADF) emitters are confined effectively. The operational stability of the phosphorescent OLED (PHOLED) using the synthesized HTM was about 15 times longer than that of the PHOLED using 2,2′-bis­(3-ditolylaminophenyl)-1,1′-biphenyl. The optimized green PHOLED exhibits EQE of over 20% for a luminance of 10 to 10,000 cd m–2 and an expected half lifetime of over 10,000 h with an initial luminance of 1000 cd m–2. The synthesized HTM is effective for improving the efficiency of OLEDs incorporating a green TADF emitter, as well as green phosphorescent OLEDs.

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9,10-Di-tert-butyl-9,10-dihydro-9,10-disilaanthracenes (trans-3 and cis-3) were synthesized, and their structures were determined by X-ray crystallography. The trans and cis isomers have a different conformation of the disilacyclohexadiene rings:  trans-3 has a chair-like structure, while cis-3 has a boat-like structure. On irradiation of a solution of trans-3 or cis-3 in the presence of di-tert-butyl peroxide, trans-3 and cis-3 isomerized to each other and reached an equilibrium to give a mixture of cis-3 (81%) and trans-3 (19%). The isomerization shows the inversion of the radical center of the intermediate silyl radicals, which is rare in reactions of silyl radicals. Considering the reaction mechanism, the silyl radicals derived from trans-3 and cis-3 are found to be relatively stable, probably due to bulky tert-butyl substituents.