Fused tetracyclic tris[1,2,4]triazolo[1,3,5]triazine as a novel rigid electron acceptor for efficient thermally activated delayed fluorescence emitters

Tris[1,2,4]triazolo[1,3,5]triazine, a new acceptor based on a fused triazole and triazine moiety, is utilized to construct D₃–A star-shaped tristriazolotriazine derivatives, named 3,7,11-tris(4-(10H-phenoxazin-10 yl)phenyl)tris([1,2,4]triazolo)[1,3,5]triazine (TTT-PXZ) and 3,7,11-tris(4-(9,9-dimethylacridin-10(9H)yl)phenyl)tris([1,2,4])triazolo[1,3,5]triazine (TTT-DMAC). Both TTT-PXZ and TTT-DMAC emitters feature TADF activities and AIEE properties. Consequently, solution processed OLEDs based on TTT-PXZ green emitters exhibited good performances, with an external quantum efficiency (EQE) of up to 6.2%.

Tris[1,2,4]triazolo[1,3,5]triazine, a new acceptor based on a fused triazole and triazine moiety, has been utilized to construct two new star-shaped TADF emitters.

An overview on synthetic strategies for the construction of star-shaped molecules

Strategies for the synthesis of star-shaped molecules have been in high demand in the last decades due to the importance of those compounds in various fields. The distinctly different properties of these compounds compared to their linear analogues make them versatile building blocks for the formation of mesophases of interesting mesomorphic and photophysical properties. Moreover, the applications of star-shaped molecules as building units for dendrimers as well as in supramolecular host-guest chemistry have also been recently studied. The star-shaped molecules mentioned in this review are classified according to the central core as well as the type of side arms. The properties and applications of these compounds are described in the appropriate contexts. This report summarizes the recent advances in this area.

Synthetic Approaches to Star-Shaped Molecules with 1,3,5-Trisubstituted Aromatic Cores

Herein, we summarize the synthetic approaches that have been developed for the synthesis of star-shaped molecules. Typically, to design such highly functionalized molecules, simple building blocks are first assembled through trimerization reactions, starting from commercially available starting materials. Then, these building blocks are synthetically manipulated to generate extended star-shaped molecules. We also discuss the syntheses of star-shaped molecules that contain 2,4,6-trisubstituted 1,3,5-triazine or 1,3,5-trisubstituted benzene rings as a central core and diverse substituted styrene, phenyl, and fluorene derivatives at their periphery, which endows these molecules with extended conjugation. A variety of metal-catalyzed reactions, such as Suzuki, Buchwald-Hartwig, Sonogashira, Heck, and Negishi cross-coupling reactions, as well as metathesis, have been employed to functionalize a range of star-shaped molecules. The methods described herein will be helpful for designing a wide range of intricate compounds that are highly valuable in the fields of supramolecular chemistry and materials science. Owing to space limitations, we will not cover all of the publications on this topic. Instead, we will focus on examples that were reported by our research group and other relevant recent literature. Apart from the trimerization sequence, this Minireview has been structured based on the key reactions that were used to prepare the star-shaped molecules and other higher analogues. Finally, some examples that do not fit into this classification are discussed.

Alcohol-Soluble Electron-Transport Materials for Fully Solution-Processed Green PhOLEDs

Two alcohol-soluble electron-transport materials (ETMs), diphenyl(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)phosphine oxide (pPBIPO) and (3,5-bis(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)diphenylphosphine oxide (mBPBIPO), have been synthesized. The physical properties of these ETMs were investigated and they both exhibited high electron-transport mobilities (1.67×10^-4 and 2.15×10^-4  cm²  V^-1  s^-1 ), high glass-transition temperatures (81 and 110 °C), and low LUMO energy levels (-2.87 and -2.82 eV, respectively). The solubility of PBIPO in n-butyl alcohol was more than 20 mg mL^-1 , which meets the requirement for fully solution-processed organic light-emitting diodes (OLEDs). Fully solution-processed green-phosphorescent OLEDs were fabricated by using alcohol-soluble PBIPO as electron-transport layers (ETLs), and they exhibited high current efficiencies, power efficiencies, and external quantum efficiencies of up to 38.43 cd A^-1 , 26.64 lm W^-1 , and 10.87 %, respectively. Compared with devices that did not contain PBIPO as an ETM, the performance of these devices was much improved, which indicated the excellent electron-transport properties of PBIPO.