Ultrathin non-doped thermally activated delayed fluorescence emitting layer for highly efficient OLEDs.

We report highly efficient, ultrathin non-doped green and bluish-green organic light-emitting diodes (OLEDs) using a thermally activated delayed fluorescence (TADF) emitter. The green OLED with an ultrathin (∼1 nm) EML showed a 2.6-fold higher external quantum efficiency (EQEmax) of 13.5% with a luminance of 17 250 cd m-2 than the conventional (30 nm) non-doped device.

Intermolecular CDC amination of remote and proximal unactivated Csp3 -H bonds through intrinsic substrate reactivity - expanding towards a traceless directing group.

An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is γ to the appended group and decreases by moving from γ → δ → ε positions. In -COO- linked alkyl chains, the same distal γ-selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N-H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote Csp3 -H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > α to keto > distal methylene (γ > δ > ε). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.

Bu4NI-Catalyzed, Radical-Induced Regioselective N-Alkylations and Arylations of Tetrazoles Using Organic Peroxides/Peresters.

Bu4NI-catalyzed regioselective N2-methylation, N2-alkylation, and N2-arylation of tetrazoles have been achieved using tert-butyl hydroperoxide (TBHP) as the methyl source, alkyl diacyl peroxides as the primary alkyl source, alkyl peresters as the secondary and tertiary alkyl sources, and aryl diacyl peroxides as the arylating source. These reactions proceed without pre-functionalization of tetrazole and in the absence of any metal catalysts. Here, peroxides serve the dual role of oxidants as well as alkylating or arylating agents. Based on DFT calculations, it was found that spin density, transition-state barriers (kinetic control), and thermodynamic stability of the products (thermodynamic control) play essential roles in the observed regioselectivity during N-alkylation. This radical-mediated process is amenable to a broad range of substrates and provides products in moderate to good yields.

Synthesis of esters via sp(3) C-H functionalisation.

Oxidative C-O bond formation via sp(3) C-H functionalisation represents an attractive approach for the synthesis of esters. This review focuses on the recent advances of sp(3) C-H bond functionalisation strategies for ester synthesis from unconventional precursors using transition metal/metal free catalysts in combination with various oxidants. Various classes of esters and the mechanisms of their formation are discussed with numerous examples.

Pd(II)/CuBr2 catalysed keto α-C(sp3)-H benzoxylation of N,N-dialkylamides directed by o-hydroxy groups.

A hydroxy group directed keto α-C(sp3)-H benzoxylation of amides, including N,N-dialkylamides and cyclic amides, has been accomplished involving ortho-hydroxy substrates possessing either an aldehydic or a keto methyl (-COCH3) group with a Pd(II)/CuBr2 catalytic combination. The carboxy group obtained via the in situ oxidation of -CHO or -COCH3 groups of ortho-hydroxy substrates then undergoes a cross-dehydrogenative coupling (CDC) with amides to furnish an α-benzoxylation product with concurrent aromatic ring bromination.

Bu4NI Catalyzed C-N Bond Formation via Cross-Dehydrogenative Coupling of Aryl Ethers (Csp3-H) and Tetrazoles (N-H).

Intermolecular C-N bond formations via cross-dehydrogenative coupling (CDC) of aryl ethers and tetrazoles have been developed under a metal-free condition. In the presence of catalytic amount of tetrabutylammonium iodide (TBAI) and aqueous TBHP, aryl ethers coupled efficiently with tetrazoles to afford hemiaminal ethers. This strategy showed high level of regioselectivity for substrates possessing multiple sp(3) C-H bonds adjacent to the ethereal oxygen.

Synthesis of 1,2,4-Triazoles via Oxidative Heterocyclization: Selective C-N Bond Over C-S Bond Formation.

The higher propensity of C-N over C-S bond forming ability was demonstrated, through formal C-H functionalization during the construction of 4,5-disubstituted 1,2,4-triazole-3-thiones from arylidenearylthiosemicarbazides catalyzed by Cu(II). However, steric factors imparted by the o-disubstituted substrates tend to change the reaction path giving thiodiazole as the major or an exclusive product. Upon prolonging the reaction time, the in situ generated thiones are transformed to 4,5-disubstituted 1,2,4-triazoles via a desulfurization process. Two classes of heterocycles viz. 4,5-disubstituted 1,2,4-triazole-3-thiones and 4,5-disubstituted 1,2,4-triazoles can be synthesized from arylidenearylthiosemicarbazides by simply adjusting the reaction time. Desulfurization of 1,2,4-triazole-3-thiones is assisted by thiophilic Cu to provide 1,2,4-triazoles with concomitant formation of CuS and polynuclear sulfur anions as confirmed from scanning electron microscope and energy dispersive X-ray spectroscopy measurements. A one-pot synthesis of an antimicrobial compound has been successfully achieved following this strategy.

Generation of bis-acyl ketals from esters and benzyl amines under oxidative conditions.

Treatment of benzylamines with esters at an elevated temperature are expected to give amides. However, in the presence of TBAI/TBHP, esters possessing a methylene carbon α-to oxygen with benzylamines provide bis-esters rather than the expected amides. Benzylamines under oxidative conditions generate less nucleophilic carboxylates, which couples at the sp(3) C-H bonds of esters and cyclic ethers to give bis-acyl ketals and α-acyloxy ethers, respectively.