Liquid Crystalline Polythiophene Bearing Phenylnaphthalene Side-Chain

Polythiophene bearing a 2-phenylnaphthalene side group at 3-position was synthesized from a 2,5-dibromothiophene monomer by two polymerization methods, i.e., Yamamoto dehalogenative polycondensation using Ni­(cod)₂ and Ni-catalyzed chain-growth polymerization. Polymers prepared by the former method had good solubility for organic solvents, 6300–8400 g mol^–1 of number-average molecular weights, absorption bands at around 300 and 385 nm due to π–π* transitions at the phenylnaphthalene moiety and polythiophene backbone, a main fluorescence emission band at around 540 nm from the polythiophene backbone in solution and film state, and presence of enantiotropic liquid crystalline phases which enabled to construct an arrayed state. On the other hand, the latter polymer showed considerably red-shifted absorption and emission bands at around 444 and 585 nm in solution and 509 and 720 nm in film state respectively, but had poor solubility and unresolved mesophases

Novel Hole-Transporting Materials with High Triplet Energy for Highly Efficient and Stable Organic Light-Emitting Diodes

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 <i>o</i>,<i>o</i>′-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