light-emitting diodes (OLEDs) and are advancing to replace the current stateof-the-art phosphorescent emitters. [1][2][3][4][5][6][7][8][9][10][11][12] Based on the thermal up-conversion of triplet excitons into singlet excitons via reverse intersystem crossing (RISC), TADF emitters can attain 100% internal quantum efficiency like phosphorescent emitters, and they can easily overcome the disadvantages of phosphorescent emitters such as high cost, need for rare materials, and environmental sustainability. [13][14][15][16][17] The emitting material used in TADF OLEDs plays a key role in controlling the important device parameters such as efficiency, lifetime, and color purity of the device. Two contradictory requirements, that is, high photoluminescence quantum yield (PLQY) and a small energy gap (ΔE ST ) between the lowest singlet (S 1 ) and triplet (T 1 ) excited states need to be balanced in the design of highly efficient TADF emitters. Although highly efficient blue and green TADF OLEDs with more than 30% external quantum efficiency (EQE) were reported recently, [18][19][20][21][22][23][24][25][26][27] it is challenging to design high-efficiency pure red emitters because of the inherent limitation of the energy gap law. [28,29] Especially, in the design of pure red TADF emitters with emission wavelengths more than 600 nm, internal conversion (IC) (non-radiative decay) of In spite of recent research progress in red thermally activated delayed fluorescence (TADF) emitters, highly efficient solution-processable pure red TADF emitters are rarely reported. Most of the red TADF emitters reported to date are designed using a rigid acceptor unit which renders them insoluble and unsuitable for solution-processed organic light-emitting diodes (OLEDs). To resolve this issue, a novel TADF emitter, 6,7-bis(4-(bis(4-(tert-butyl)phenyl) amino)phenyl)-2,3-bis(4-(tert-butyl)phenyl)quinoxaline-5,8-dicarbonitrile (tBuTPA-CNQx) is designed and synthesized. The highly twisted donoracceptor architecture and appropriate highest occupied molecular orbital/ lowest unoccupied molecular orbital distribution lead to a very small singlettriplet energy gap of 0.07 eV, high photoluminescence quantum yield of 92%, and short delayed fluorescence lifetime of 52.4 µs. The peripheral t-butyl phenyl decorated quinoxaline acceptor unit and t-butyl protected triphenylamine donor unit are proven to be useful building blocks to improve solubility and minimize the intermolecular interaction. The solution-processed OLED based on tBuTPA-CNQx achieves a high external quantum efficiency (EQE) of 16.7% with a pure red emission peak at 662 nm, which is one of the highest EQE values reported till date in the solution-processed pure red TADF OLEDs. Additionally, vacuum-processable OLED based on tBuTPA-CNQx exhibits a high EQE of 22.2% and negligible efficiency roll-off.

Described herein is the first iridium-catalyzed cyclative indenylation through sequential B(4)–C and intramolecular C–C bond formation from o-carboranes and propargyl alcohols, leading to the formation of B(4)-indenylated o-carboranes with excellent regioselectivity via direct B–H activation. Moreover, the iridium-catalyzed regioselective 1,3-dienylation has been accessed through sequential B–H activation, dehydration, and decarboxylation, producing B(4)-dienylated o-carboranes.

No abstract

Palladium-catalyzed iterative cage B–H arylation reaction of a wide range of B(4)-acylamino-o-carboranes with aryl iodides has been developed, leading to the formation of B­(5,8,9)-triarylated B(4)-acylamino-o-carboranes with excellent regioselectivity. Moreover, B­(5,8,9)-triarylated carboranes bearing three different aryl groups were synthesized from B(4)-acylamino-o-carborane and three different aryl iodides. The order of introduction [B(9) > B(8) > B(5)] of aryl groups into the B­(5,8,9)-triarylation reaction was determined for the first time through NMR monitoring and X-ray analyses.

No abstract