We demonstrate two efficient blue-green thermally activated delayed fluorescence (TADF) compounds comprising a dimeric phenylcarbazole and four cyano substituents on the phenyl rings. A comparison of the 2,6-dicyano-substituted derivative (26IPNDCz) with the 3,5-dicyano-substituted derivative (35IPNDCz) shows that 26IPNDCz provides a larger dihedral angle and a lower decrease in the energy difference between the first singlet and triplet excited states (¦E ST ) and the TADF lifetime. An organic light-emitting diode based on 26IPNDCz afforded an external quantum efficiency of 10% with reduced efficiency roll-off.Organic light-emitting diodes (OLEDs) have attracted much interest recently because of their potential application in flat-panel displays and light sources. In OLEDs containing only fluorescent dyes, the internal quantum efficiency (IQE) is limited to 25% because of the exciton branching ratio of singlet states. Phosphorescent OLEDs containing noble-metal-based phosphors can harvest the remaining 75% triplet excitons and can thus achieve 100% internal quantum efficiency.1,2 However, the drawback of phosphorescent OLED materials is their cost. Recent progress in OLEDs development has focused on lowcost solutions to improve the device efficiency. A promising way is to harvest triplet excitons in fluorescent OLEDs by triplettriplet annihilation (TTA) or thermally activated delayed fluorescence (TADF). TTA comprises intermolecular fusion, in which one singlet and one ground state can be produced from two triplet states. Thus, the upper IQE limit of OLEDs made using TTA can increase to 63% (0.25 + 0.75 © 0.5). Assuming that the optical outcoupling is 0.20, the maximum external quantum efficiency (EQE) is estimated to be 13%. 3 In 2009, the EQE of TTA devices was reported to be 11%, which is very close to the theoretical limit.3 On the other hand, triplets can also be converted to singlets by reverse intersystem crossing (RISC) under thermal activation when the energy difference between the first singlet (S 1 ) and triplet (T 1 ) excited states (¦E ST ) is small enough. 4,5 In 2012, our group demonstrated that an OLED with a green TADF emitter composed of a carbazole donors (D) and a dicyanobenzene acceptor (A) can achieve an EQE as high as 19%, corresponding to an IQE of nearly 100%. 6 At the same time, pure blue and orange-red TADF OLEDs have also achieved high EQEs of 10% and 17.5%, respectively. 7a,7b However, their EQE roll-off at high current density is rather significant because of their long TADF lifetimes. We, thus, investigated the photophysical mechanism of TADF emitters in detail and further demonstrate molecular design principles.According to the Boltzmann statistics, a small ¦E ST is essential for the efficient thermally activated repopulation of the emissive S 1 state; this also governs the TADF lifetime. To achieve a small ¦E ST , a small overlap between the occupied and unoccupied orbitals involved in the excitation is necessary, CT in some cases.9,10 A comparison with the carbazolyldicyanobenz...

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In situ click chemistry has great potential for identifying enzyme inhibitors. However, conventional in situ click chemistry provides extremely low yields of the products, making it incompatible with direct activity-based assays. Here, to address this issue, we focused on the catalysis of azide–alkyne cycloaddition (AAC) by the metal ion in metalloproteins. We chose 2-ethynyl N-heterocompounds as alkyne fragments which are activated by coordination to the metal ion. For proof of concept, we applied metal ion-catalyzed in situ AAC to identify inhibitors of Fe­(II)-dependent lysine demethylase 5C (KDM5C). The triazole product was obtained in dramatically high yield, dependently on Fe­(II) in KDM5C, and the metalloprotein-catalyzed click reaction was compatible with activity-based high-throughput screening, enabling us to discover a potent KDM5C inhibitor. Thus, metal-catalyzed in situ AAC should be generally applicable to other metalloproteins.

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Asymmetric 1,4-addition reaction of arylboronic acid to cyclic enone was carried out in the presence of a chiral ferrocene-based phosphine ligand–palladium catalyst. The reaction of 2-cyclohexen-1-one by palladium complex with (S,Rp)-[1-(2-bromoferrocenyl)ethyl]diphenylphosphine afford a optically active β-arylcyclohexanone in good yield up to 71% ee.