Oxidative C−C coupling of carbazoles possessing various substituents is demonstrated in the presence of organic (metal-free) recyclable oxidants, such as DDQ or CA/H + , for accessing bicarbazole regioisomers. Differently substituted carbazoles are examined to showcase regioselective discrimination (3,3′-versus 1,3′-bicarbazoles) and preferences based on sterics and electronics in oxidative coupling. Finally, a mechanism that involves the carbazole radical cation has been traced (evidenced) and proposed on the basis of the UV−vis−NIR absorption and EPR spectroscopy results. This study underlines the strategic chemical preparation of a series of bicarbazoles in an efficient manner.

A variety of arylamines are shown to undergo oxidative C-C bond formation using quinone-based chloranil/H reagent as the recyclable organic (metal-free) oxidant system to afford benzidines/naphthidines. Arylamines (3°/2°) designed with various substituents were employed to understand the steric as well as electronic preferences of oxidative dimerization, and a mechanism involving amine radical cation has been proposed. The tetraphenylbenzidine derivative obtained via oxidative C-C coupling has been further converted to blue-emissive hole-transporting material via a simple chemical transformation. This study highlights the preparation of novel HTMs in a simple, economic, and efficient manner.

In this study, we synthesized three simple and inexpensive (34−120 USD/g) 3,3′-bicarbazole-based hole transporting materials (BC-HTMs; NP-BC, NBP-BC and PNP-BC) through a metal-free oxidative coupling, in excellent yields (≥95%). These bicarbazoles contain phenylene or biphenylene substituents on the carbazole N atom, with extended π-conjugation achieved through phenylene units at the 6,6′-positions of the bicarbazole. When using NBP-BC as a dopant-free HTM in a p−i−n perovskite solar cell (PSC), we achieved a power conversion efficiency (PCEs) of 12.22 ± 0.54% under AM 1.5G conditions (100 mW cm −2 ); this PCE was comparable to that obtained when using PEDOT:PSS as the HTM (11.23 ± 1.02%). BC-HTMs showed the large grain size (μm) of perovskite than PEDOT:PSS-based, due to defect passivation on indium tin oxide (ITO) substrate and good hydrophobicity. Furthermore, we realized highly efficient and stable PSCs when using the p−i−n device structure ITO/NiO x /NP-BC/perovskite/PC 61 BM/BCP/Ag. The bifacial defect passivation effect of the interfacial layer improved the grain size of the perovskite layer and also enhanced the performance; the best performance of the NiO x /NP-BC device was characterized by a short-circuit current density (J sc ) of 22.38 mA cm −2 , an open-circuit voltage (V oc ) of 1.09 V, and a fill factor (FF) of 79.9%, corresponding to an overall PCE of almost 20%. This device structure has competitive potential because its performance is comparable to that of the record-high-efficiency PSCs. Under an Ar atmosphere, the PCE of the NiO x /NP-BC PSC device decayed by only 4.55% after 168 h; it retained 90.80% of its original PCE after 1000 h. A morphological study revealed that the films of the BC-HTMs were indeed smooth and hydrophobic and that the perovskite films spin-coated upon them were uniform and featured large grains (micrometer scale). Time-resolved photoluminescence (TRPL) spectra of the perovskite films suggested that the hole extraction capabilities of the NiO x /BC-HTMs were better than that of the bare NiO x . The superior film morphologies of the NiO x /BC-HTMs were responsible for the performances of their devices being comparable to those of bare NiO x -based PSCs.

New heteroacenes, named coumarinacenes, have been designed, synthesized and characterized. They possess visible absorption and orange-red emission that are far beyond those of benzo[g]coumarins. They exhibit deep HOMO energy levels, and reveal excellent thermal, photochemical and air sta-Coumarins are pyranone-annulated benzenes (2H-benzopyran-2-ones) that are ubiquitous in nature. [1] They are actually popular for their wide spectrum of biological and pharmacological activities, [2a] such as, antioxidant, [2b] antidepressant, [2c] anticoagulant, [2d] anti-inflammatory, [2e] antifungal, [2f ] antitumor, [2g] anti-HIV, [2h] antibiotic, [2i] etc., and for their excellent biocompatibility. [1] Structurally simple derivatives of coumarin exhibit rich photophysical and photochemical properties (high photoluminescence quantum yields, large Stokes shifts and good photostability) paving their entry into modern photonic applications; laser dyes, [3a,3b] non-linear optics, [3c] two-photon bioimaging [3d] and sensing [3e] are some examples. Moreover, coumarin derivatives are recently being exploited as functional materials in organic light emitting devices, [4a,4b] liquid crystals, [4c] dye-sensitized solar cells, [4d,4e] electron and energy transfer systems, [4f,4g] and fluorescent probes. [4h] Despite the broad utility of coumarins, the low-lying absorption and emission wavelengths (due to shorter conjugation lengths) are primarily the bottlenecks in furthering their applications. In an effort to overcome the limitations, considerable attention is devoted in recent times for the development of novel π-expanded coumarin dyes. [5] Benzocoumarins-the simplest π-expanded benzene-fused coumarins-indeed absorb and emit light in the longer wavelength region when compared to parent coumarins (Scheme 1). [6] Among the other isomeric [a] A

Differently-linked bithienyl-attached fluorenes have been synthesized. While the oxidative photodicyclization of 2,3'-bithiophene-containing fluorene was successful to yield tetrathieno-fused regioisomeric π-expanded fluorenes, the reaction with 2,2'-bithiophene-containing fluorene was very sluggish. Interestingly, the connectivity in bithiophenes appears to determine the (photo)reactivity. On the one hand, under mild Scholl conditions, 2,3'-bithiophene-containing fluorene yielded a highly regioselective product while 2,2'bithiophene-containing fluorene led to polymerization. The optical and electrochemical properties of tetrathienoannulated π-expanded fluorenes were investigated, and they were found to be quite different from those of the phenanthrenoannulated π-expanded analogues. These newly obtained sulfur-edged π-expanded fluorenes may hold promise in organic electronics.

While intramolecular Scholl oxidative coupling between two arenes is common, successful CÀ C heterocoupling between thiophene and arene is scarce. The latter is due to the notorious reactivity of thiophene towards polymerization under oxidative conditions. This report systematically demonstrates how topological variation of electronics and reactivity in thiophene substrates can lead to efficient oxidative heterocoupling. Bis(biaryl)thiophenes having reactive αand β-positions open are the choice of substrates. The cyclizing arene partners are so electronically tuned for thiophene's reactivity (at αand β-) as to establish CÀ C bond oxidatively generating symmetrical as well as unsymmetrical diphenanthrothiophenes which are basic thiananographenes. Depending on the cyclizing-couple's electronics, either areneor thiophene-centered oxidation initiates CÀ C heterocoupling. The potential utility of these simple thiananographenes is further unfurled by converting them to functional NÀ /Cgraphene segments that are aza-corannulene precursor and tetrabenzospirobifluorene. Their bright emission and extended electrochemical stability are remarkable that may be potentially important and applicable.

The Cover Feature shows a representation of a 21st century molecular unition (the act of joining of hands) of the 19th century molecular couple (structures in blue) with a purpose of rediscovering a new life together (structure in red). More information can be found in the Communication by S. Dutta, P. Venkatakrishnan et al.