Long-wavelength materials are key for development of pure-color and white organic light-emitting devices (OLEDs). An organic molecule, combining hybridized local electron and charge-transfer (HLCT) states and aggregation-induced emission (AIE), not only breaks the 5% external quantum efficiency (EQE) limit but also overcomes emission quenching. Herein, we designed and synthesized four novel donor–acceptor compounds of TBAN, TBT, TBAT, and TABAT using triphenylamine (TPA) as the donor, benzothiadiazole (BT) as the acceptor, and anthracene (AN) as a bridge. We found that the emission peaks of TBAN, TBT, TBAT and TABAT are located at 596, 615, 580 and 546 nm, respectively. We successfully applied them to non-doped OLEDs, and the resulting devices exhibited excellent performance. For example, the optimal TBAN-based OLEDs showed a maximum luminance of 74 820 cd m⁻², a current efficiency of 12.1 cd A⁻¹ and a maximum EQE of 5.7% with low roll-off. Additionally, the device with TBAN as both the emitter and hole-transport material also exhibited high efficiency that is comparable to that of an NPB-based device. This work demonstrates that it is feasible to obtain excellent orange and red emitters by employing BT- and TPA-based D–A architectures.

We have designed and synthesized four bipolar materials, TAZ-1Cz, TAZ-2Cz, TAZ-3Cz and TAZ-4Cz, using 2-(2-phenyl-2H-1,2,4-triazol-3-yl)pyridine (TAZ) as an electron-withdrawing group and phenylcarbazole as an electron-donating group. Their rigid molecular structures improve their thermal stability with high glass transition temperatures: 99 °C for TAZ-2Cz, 100 °C for TAZ-3Cz and 103 °C for TAZ-4Cz. Employing TAZ-1Cz, TAZ-2Cz, TAZ-3Cz and TAZ-4Cz as hosts, green phosphorescent organic light-emitting devices (PhOLEDs) with fac-tris(2-phenylpyridine)iridium as an emitter display maximum external quantum efficiencies (EQEs) of 15.8, 15.5, 16.0 and 13.0%, respectively. And blue PhOLEDs hosted by TAZ-1Cz, TAZ-2Cz and TAZ-3Cz achieved maximum current efficiencies of 8.6, 11.0 and 10.6 cd A⁻¹, respectively. Furthermore, non-doped OLEDs using TAZ-1Cz and TAZ-4Cz as emitters exhibit electroluminescence (EL) peaks at 400 and 412 nm with CIE coordinates of (0.16, 0.04) and (0.15, 0.04), which are located in the deep-blue region.

It is indispensable to synthesize deep-blue light emitting materials with high luminous efficiency for realizing full-colour organic light emitting diode (OLED) displays. The hybridized local and charge-transfer (HLCT) state is a special excited state that hybridizes the local state and the charge transfer state to ensure a high fluorescence quantum yield (η_pl). Herein, a blue fluorescent material of TPA-DFCP was designed and synthesized, with a twisted D–π–A configuration, in which triphenylamine (TPA), benzonitrile (CP) and 9,9-dioctylfluorene serve as the D, A, and π-conjugation unit, respectively. It also exhibits good solubility and can be dissolved in several organic solvents with different polarities. The non-doped device, with TPA-DFCP as the emitter, shows excellent electroluminescent (EL) efficiency with a maximum EQE of 7.74%. Furthermore, the doped device of TPA-DFCP exhibits excellent deep-blue emission with the EL emission peak at 436 nm and the CIE coordinates at (0.153, 0.077), which are very close to the NTSC standard blue CIE (x, y) coordinates of (0.140, 0.080). Meanwhile, the doped device also exhibited excellent EL performance, with a maximum external quantum efficiency (EQE) and radiative exciton utilization (η_r) of 8.30% and 57.67%, respectively.

Achieving an external quantum efficiency exceeding 5% for traditional blue fluorescent organic light emitting devices (OLEDs) is still a current challenge due to the 25% limit of the radiative exciton yield. Bipolar organic molecules with a special hybrid local-excited and charge-transfer state have showed huge potential to address this issue. Herein, we designed and synthesized two novel bipolar compounds, namely TPA-AN-NA and TPA-AN-TFP, which were structured by simply linking a donor of triphenylamine (TPA) and both acceptors of anthracene derivatives. Both resulting compounds show good blue emission with emission peaks at 468 and 471 nm and photoluminescence quantum yields of 30.68 and 23.96% in thin films for TPA-AN-NA and TPA-AN-TFP, respectively. They also exhibit good solubility and can dissolve in several organic solvents with different polarities. Further, the fabricated blue OLEDs with TPA-AN-NA and TPA-AN-TFP as emitters also realize the corresponding blue emission well with electroluminescence peaks at 464 and 472 nm, respectively. The TPA-AN-NA-based blue device achieves a high external quantum efficiency of 5.44% and a radiative exciton yield of 56.68%, exceeding the theoretical limit.

Multifunctional materials with aggregation-induced emission (AIE), mechanochromic luminescence and electroluminescent (EL) features in organic light-emitting devices (OLEDs) are demonstrated to be promising applications in many fields. Herein, we present our work on TQT, using quinoxaline as an acceptor and triphenylamine (TPA) as a donor with a D–A–D symmetrical structure. TQT exhibits high-contrast polymorph-dependent emission, from green to red, and multicolor mechanochromic luminescence (MCL) in aggregate states. Five different crystals (TQT-G = 530 nm, TQT-Y = 575 nm, TQT-Y1 = 584 nm, TQT-O = 593 nm, and TQT-R = 600 nm) were obtained via the slow evaporation of a mixed solution. All crystals and powder phases switch to showing emission at 546 nm after grinding. Among them, TQT-G exhibited remarkable H-aggregate behavior, while TQT-Y tends to form a J-aggregate state. TQT-G and TQT-Y1 have similar configurations and packing models but completely different emission characteristics. A doped device with 20 wt% TQT and a non-doped device showed good electroluminescence performance.