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Self-host thermally activated delayed fluorescence (TADF) materials have recently been identified as effective emitters for solution-processed nondoped organic light-emitting diodes (OLEDs). However, except for the carbazole unit, few novel dendrons have been developed to build self-host TADF emitters. This study reports two self-host blue materials, tbCz-SO and poCz-SO, with the same TADF emissive core and different dendrons. The influence of the peripheral dendrons on the photophysical properties and electroluminescent performances of the self-host materials were systematically investigated. The transient fluorescence and electroluminescence spectra indicated that the diphenylphosphoryl carbazole units could effectively encapsulate the emissive core to reduce the concentration quenching effect and to enhance reverse intersystem crossing. By using tbCz-SO and poCz-SO as host-free blue emitters, the performance of the solution-processed nondoped OLED device demonstrated that a more balanced charge transfer from the bipolar dendrons would offer a better current efficiency of 10.5 cd A−1 and stable color purity with Commission Internationale de L'Eclairage units of (0.18, 0.27). [ABSTRACT FROM AUTHOR]

Three bipolar hosts composed of electron-accepting diphenylphosphine oxide and electron-donating carbazole/triphenylamine have been synthesized and characterized. With structural topology modification, the particular physical properties of the materials can be subtly optimized, such as the thermal stability, singlet–triplet energy gap and charge balance ability. Both DFT calculation and experiment results demonstrate that the introduced triphenylamine can effective minimize the HOMO–LUMO energy gap, while the carbazole units can prevent the excited energy loss and keep high triplet energy ( E T = 3.0 eV) due to the enhanced molecular rigidity. As a result, solution-processed blue PHOLEDs exhibited a high current efficiency of 25.2 cd A −1 and a power efficiency of 11.5 lm W −1 , which implies that the unique molecular modulation is very cost-effective and competitive for the device performance improving. [ABSTRACT FROM AUTHOR]

Two bipolar materials based on 9-phenylcarbazole and diphenyl sulfone for nondoped deep blue OLEDs, namely bis-(4-benzenesulfonyl-phenyl)-9-phenyl-9 H- carbazoles, have been designed and synthesized by Suzuki coupling reactions. Their thermal, photophysical, and electrochemical properties have been systematically investigated. The nondoped devices using 3,6–bis–(4-benzenesulfonyl-phenyl)-9-phenyl-9 H -carbazoles and 2,7-bis-(4-benzenesulfonyl-phenyl)-9-phenyl-9 H -carbazoles as the emitters show deep blue emission color with peaks at 424 and 444 nm, and the Commission Internationale de l׳Eclairage (CIE) coordinates of (0.177, 0.117) and (0.160, 0.117), respectively. Furthermore, these materials based devices have high color-purity with small width at half-maximum (FWHM) of 65 and 73 nm, respectively. The results provide a novel approach for the design of deep blue emitter for nondoped OLEDs. [ABSTRACT FROM AUTHOR]

Two novel phenylcarbazole/diphenylphosphine oxide derived, alcohol soluble host materials for solution-processed, blue phosphorescent organic light-emitting devices were designed and synthesized. The thermal stability, photophysical and electrochemical properties of these host materials have been investigated in detail. These hosts both exhibited high triplet energy levels, which ensure efficient energy transfer from hosts to the triplet emitter iridium(III) bis(4,6-difluorophenylpyridinato)picolinate. The new host compounds also showed good film morphology and bipolar charge transport properties. Multilayer solution-processed blue electrophosphorescent organic light-emitting diodes using the new host compounds with the triplet emitter iridium(III) bis(4,6-difluorophenylpyridinato)picolinate exhibited high luminance efficiency of 27.8 cd A −1 , which was outstanding with respect to other work reported for solution-processed blue PhOLEDs. [ABSTRACT FROM AUTHOR]

N –phenyl carbazole and triphenylamine functionalized tris(aryl)triazines, as well as the corresponding mononers, have been synthesized by Suzuki cross–coupling reactions. The electronic, photophysical and electrochemical properties of these materials can be effectively tuned by manipulation of the constitution of acceptor and donor units. N –phenyl carbazole and triphenylamine functionalized 2,4,6–trisphenyl–1,3,5–triazines exhibit small energy gaps between the singlet and triplet (0.24 eV and 0.18 eV), and offer potential for application as thermally activated delayed fluorescence materials. The results are supported by time–dependent density functional theory calculations, delayed and time-resolved fluorescence data. [ABSTRACT FROM AUTHOR]

Suppressing non-radiative channel in luminescent polymer is the key factor for high device efficiency of organic light-emitting diodes (OLEDs). In this paper, we synthesized three side-chain TADF polymers, PTRZ-TRZ, PTRZ-TPA and PTRZ-Cz, to deeply investigate the relationship between energy transfer and molecular structure. The photophysical measurements show that the copolymerized monomer has significant effect on the exciton deexcitation process of TADF fragment. The rigid carbazole unit can efficiently separate the TADF units to inhibit the aggregation-caused quenching (ACQ) of polymer, while electron-donating triphenylamine unit will induce the severe charge transfer state to form low energy exciplex, which lead to severe energy leakage of the excited TADF. Moreover, according to the single-charge devices test, the ideal separation unit also can improve the capability of charge injection and carrier balance. As a result, the solution-processed OLEDs host with PTRZ-Cz achieved the external quantum efficiency (EQE max) of 14.2%, which was much higher than that of PTRZ-TPA and PTRZ-TRZ. By doping red phosphorescent emitter Ir(MDQ) 2 (acac), the hybrid white OLED devices (T-P WOLEDs) based on PTRZ-Cz achieved the maximum current efficiency (CE max), power efficiency (PE max) and EQE max of 46.8 cd/A, 32.6 lm/W and 20.7%, respectively, with a high CRI of 80.6. The outcomes obtained in this study can provide useful insights into the structure−property relationship for further development of efficient TADF polymer hosts for solution-processable OLEDs. • The side chain polymers inherit TADF properties of small-molecules and reduce the aggregation-caused quenching by separating TADF units. • Suppressing the non-radiative channel in luminescent polymer by copolymerizing electron-donating monomers, and achieving 2–3 times of EQE max. • The hybrid white OLED devices achieve CE max , EQE max of 46.8 cd/A, 20.7%, respectively, with a high CRI of 80.6. [ABSTRACT FROM AUTHOR]

A series of bipolar materials for thermally activated delayed fluorescence based on 3,6-di-tert-butyl-9-((phenylsulfonyl)phenyl)-9H-carbazoles, is synthesized by Ulmann coupling reactions. In these materials, the 3,6-di-tert-butylcarbazole group is linked at the 3-, 4- position or 3′-, 4′- position of diphenyl sulfone. The effects of the conjugation connectivity on the electronic, photophysical and electrochemical properties of these materials, are studied by extensive UV-vis, fluorescence spectroscopic measurements, cyclic voltammetry and theoretical calculations as well as X-ray crystallographic analysis. The energy gap between singlet and triplet in these materials is tuned from 0.39 eV to 0.22 eV by manipulation of conjugation of the electron donor units. [ABSTRACT FROM AUTHOR]

Abstract: A novel N-phenyl carbazole substituted 2, 4,6-trisphenyl-triazine host material(TPCPZ) for solution processed green phosphorescent organic light-emitting devices (PhOLEDs) was synthesized by a Suzuki-cross coupling reaction. The optical, electrochemical and thermal properties of TPCPZ have been characterized. TPCPZ exhibits a high glass transition temperature of 165 °C and a triplet energy of 2.63 eV. The appropriate HOMO energy level (−5.39 eV) and LUMO energy level (−2.16 eV) matching with the HOMO energy level of PEDOT:PSS(−5.35 eV) and the LUMO energy level of Cs2CO3/Al bilayer cathode (−2.2 eV), facilitate the transfer of holes and electrons. The solution-processed single-layer device using TPCPZ as the host for fac-tris(2-(4-phenylpyridine)iridium (Ir(ppy)3) exhibited a low turn-on voltage of 3.5 V, a maximum current efficiency of 20.8 cd A−1 and a maximum luminance of 18,000 cd m−2. These results demonstrated that TPCPZ as a host material is advantageous for fabrication of highly efficient single-layer green PhOLEDs. [Copyright &y& Elsevier]

Abstract: A dendritic host material 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl for solution-processed blue phosphorescent organic light-emitting devices was designed and synthesized. Owing to the decrease of the π conjugation length of biphenyl moiety in molecule structure, this carbazole derived derivative shows high triplet energy. Furthermore, the thermal, photophysical and electrochemical properties of 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl were investigated. The high triplet energy of 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl ensures efficient energy transfer from the host to the triplet emitter iridium(III) bis(4,6-difluorophenylpyridinato)picolinate. The single layer device using the carbazole derivatives as the host for iridium(III) bis(4,6-difluorophenylpyridinato)picolinate showed the maximum luminance efficiencies of 5.8 cd A−1, and a maximum external quantum efficiency 2.8%. The efficiency of the carbazole derivative based device was almost 3 times higher than the corresponding 1,3-bis(9-carbazolyl)benzene based device. [Copyright &y& Elsevier]

Abstract: This paper reports the synthesis and physical properties of two novel carbazole-based dendritic host materials Cz-CCP and Cz-mCP for solution-processed blue phosphorescent organic light-emitting devices (PhOLEDs). These dendritic hosts exhibit high triplet energy (≥2.85 eV), excellent film-forming ability (with low root-mean-square (rms) values less than 0.2 nm), high glass-transition temperatures in the range of 242–248 °C, and the appropriate HOMO energy levels (−5.33–−5.35 eV) facilitating the transfer of holes from Poly(3,4-ethylenedioxythiophene):Poly(styrene-4-sulfonate) (PEDOT:PSS) to the emitting layer. The single-layer device using Cz-CCP and Cz-mCP as the host for the phosphorescence emitter iridium(III) bis(4,6-difluorophenylpyridinato)-picolinate (FIrpic) showed the maximum luminance efficiencies of 9.6 and 10.8 cd A−1, respectively. By introducing a thin 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) electron-transporting and exciton-confining layer, the maximum efficiency of the solution-processed double-layer device based on Cz-CCP and Cz-mCP can be further improved to 20.5 and 22.7 cd A−1, and maximum external quantum efficiencies as high as 10.2% and 11.5%, respectively. These results demonstrated that the newly synthesized, carbazole-based dendritic host materials are advantageous for fabrication of highly efficient blue PhOLEDs. [Copyright &y& Elsevier]

A multipolarization branched thermal activated delayed fluorescence sensor BrACCN was designed and synthesized based on cyano-carbazole. The classical molecule structure 4CzCN was used as luminescent nucleus, which was progressively branched for photophysical optimization. On the basis of the thermal activated delayed fluorescence material 4CzCN and 4Cz-CzCN , the molecular modification was optimized to achieve long fluorescence life and high quantum yield. Through research and analysis, the fluorescence quantum yield of the branched probe was 73%, which was 1.5 times higher than that of unbranched 4CzCN. The fluorescence lifetime of the probe BrACCN was doubled up to 3 μs based on the introduction of peripheral Br atoms. Meanwhile, the probe has high selectivity and sensitivity for Fe3+ ions. In the presence of multiple ions, the probe responded only to Fe3+ with a complexing mode of 1:1 and the fluorescence was turned off. The probe has a low limit of detection (LOD) of 2.9 × 10−8 mol/L for Fe3+ ions. The probe also has a strong AIE characteristic, which is extremely beneficial for the application range of the probe. Moreover, these excellent properties of the probe will offer promising applications in live-cell confocal fluorescence imaging and time-resolved fluorescence imaging. [Display omitted] • The PLQY of the encapsulated probe BrACCN is 1.5 times higher than that of unencapsulated. • The optimized TADF molecule structure has a longer fluorescence lifetime up to 3 μs. • The TADF probe can quickly recognize Fe3+ with a response time of 2 s. • The TADF probe has been proved to be used for detection of domestic drinking water. [ABSTRACT FROM AUTHOR]

A new bipolar host material t3Cz-SO was designed and synthesized by introducing tert-butyl carbazole unit to the peripheral of parent TADF units. The calculated triplet energy and ΔE ST of t3Cz-SO are 2.85 and 0.11 eV, respectively. Moreover, t3Cz-SO exhibited excellent film-forming ability and morphological stability, which are suitable for the fabrication of solution-processed OLEDs. The FIrpic-based device host with t3Cz-SO achieved low turn-on voltage of 3.5 V and high power efficiency of 16.5 lm W−1, which is almost ten times higher than the unmodified parent TADF molecule. This study shows that the introduction of tert-butyl carbazole unit to the periphery of small molecular TADF emitter is an effective method for the development of efficient electroluminescent materials. The introduction of tert-butyl carbazole around the reported TADF molecules not only effectively maintains the TADF properties of the material, but also enhance the film-forming performance and morphological stability of the material, which is significance for the preparation of solution-processed OLED devices. Image 1 • The introduced tert-butyl carbazole significantly enhance the film-forming ability and morphological stability of the TADF material. • The calculated ΔE ST of tert-butyl carbazole substituted t3Cz-SO was only 0.11 eV, which is much small than that of parent molecule Cz-SO (0.41 eV). • The t3Cz-SO achieved an improved power efficiency of 13.03 lm W−1, which is almost ten times high than the parent one. [ABSTRACT FROM AUTHOR]