Synthesis and characterization of high Tg carbazole-based amorphous hole-transporting materials for organic light-emitting devices

Novel hole-transporting materials based on carbazole dendrimers, namely G1CBC and G2CBC were synthesized and characterized. They are thermally stable with high glass transition temperatures (T_g) up to 245 °C and exhibit chemically-stable redox processes. Double-layer green OLEDs using these materials as the hole-transporting layer (HTL) with the device configuration of ITO/HTL/Alq3/LiF:Al emit brightly (λ_em 522-534 nm) from the Alq3 layer with a maximum luminance and low turn-on voltage of 15,890 cd/m² and 3.0 V, respectively. Their ability as HTLs in terms of device performance is comparable to the common hole-transporter N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB), however their thermal properties were far greater than both NPB and N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine (TPD).     

Bifunctional anthracene derivatives as non-doped blue emitters and hole-transporters for electroluminescent devices

New highly fluorescent bifunctional anthracenes showed high thermal and electrochemical stability, and great potential as both blue emitters and hole-transporters for OLEDs. Deep-blue and Alq3-based green devices with maximum efficiencies and CIE coordinates of 1.65 and 6.25 cd A(-1), and (0.15, 0.16) and (0.26, 0.49) were achieved, respectively.     

Reaction of some 4,6-dimethoxyindoles with nitric acid: nitration and oxidative dimerisation

A range of 3-substituted-4,6-dimethoxyindoles bearing electron-withdrawing groups in either the 2- or 7-position, can be nitrated using nitric acid in acetonitrile, to give 7-nitro and 2-nitro-indoles, respectively. Those without electron-withdrawing groups undergo oxidative dimerisation at C7, if 2,3-disubstituted, and at C2, if N-methylated and unsubstituted at C2.     

Synthesis, characterization, and properties of 7,7′-bis(3,6-di-tert-butylcarbazol-N-yl)-substituted fluorenyl-oligothiophenes

A series of new 7,7′bis(3,6-di-tert-butylcarbazol-N-yl)-substituted fluorenyl-oligothiophenes bearing 0-, 2-, 4-, 6-, and 8-thiophene rings, namely BCFTn, were synthesized using palladium catalyzed Stille dimerization coupling reactions of their corresponding brominated thiophenes. The relationship between the chemical structure and the properties of these oligomers was evaluated. With respect to the electronic properties, the longest wavelength absorptions, emissions, and also the oxidation potentials can be tuned by varying the conjugation length of the oligothiophene segments. The terminal carbazole and fluorene moieties of the resulting materials are beneficial for their morphology, conjugation length, and solubility.     

Bis(4-diphenylaminophenyl)carbazole end-capped fluorene as solution-processed deep-blue light-emitting and hole-transporting materials for electroluminescent devices

A new highly fluorescent bis(4-diphenylaminophenyl)carbazole end-capped fluorene (TCF) is synthesized and characterized. TCF is an amorphous molecular glass with a high glass transition temperature of 169 °C, is electrochemically stable, and gives strong blue emission both in solution and solid state. It showed greater ability as a solution processed blue emitter and hole-transporter for OLEDs than commonly used NPB. High-efficiency, deep-blue and Alq3-based green devices with luminance efficiencies and CIE coordinates of 0.93 cd/A and (0.16, 0.09), and 3.78 cd/A and (0.29, 0.45) were achieved, respectively.     

Synthesis and characterization of 9,10-substituted anthracene derivatives as blue light-emitting and hole-transporting materials for electroluminescent devices

New 9,10-substituted anthracene derivatives were designed and synthesized for application as blue-emitting and hole-transporting materials in electroluminescent devices. They were characterized by H NMR, C NMR, FTIR, UV–vis, PL spectroscopy, and mass spectrometry. The theoretical calculation of three-dimensional structure and the energy densities of HOMO and LUMO states, as well as optical properties of these new obtained materials, supported the claim that they had non-coplanar structures. Their optical, thermal, and electrochemical properties could be tuned by varying the peripheral substituents. All of them were electrochemically and thermally stable molecules. Materials having electron donating triphenylamine as peripheral substituents showed promising potential as both blue light-emitting materials and hole-transporting materials for electroluminescent devices. Efficient blue and Alq3-based green OLEDs with maximum luminance efficiencies and CIE coordinates of 1.65 cd/A and (0.15, 0.16) and 6.25 cd/A and (0.26, 0.49) were achieved, respectively.     

Synthesis and properties of stable amorphous hole-transporting molecules for electroluminescent devices

New triphenylamine-carbazole end-capped molecules were synthesized by a divergent approach using bromination and Suzuki cross-coupling reactions. All compounds showed an excellent electrochemical reversibility and a good thermal stability. They were fabricated as hole-transporting layers (HTLs) with the device configuration of ITO/HTL/Alq₃/LiF:Al. A bright green emission from the Alq₃ layer with a maximum luminance of 7500 cd/m² was observed at 9.8 V and a low turn-on voltage of 3.4 V.     

Carbazole dendronised triphenylamines as solution processed high Tg amorphous hole-transporting materials for organic electroluminescent devices

Carbazole dendrimers up to 4th generation were synthesized. They showed significantly high T(g), amorphous and stable electrochemical properties, and great potential as solution processed hole-transporting materials for OLEDs. Alq3-based green devices exhibited high luminance efficiency and CIE coordinates of 4.45 cd A(-1) and (0.29, 0.53), respectively.