A boron-substituted azobenzene, (E)-[2-(4-methoxyphenylazo)phenyl]bis(pentafluorophenyl)borane, presented the most intense fluorescence among the azobenzene derivatives.

2-[Bis(pentafluorophenyl)boryl]azobenzenes bearing hydrogen, methoxy, dimethylamino, trifluoromethyl, fluoro, n-butyl, and tert-butyldimethylsiloxy groups at the 4'-position or methoxy and bromo groups at the 4-position have been synthesized. The 4-bromo group of the 2-boryl-4-bromoazobenzene derivative was converted to phenyl and diphenylamino groups by palladium-catalyzed reactions. The absorption and fluorescence properties have been investigated using UV/Vis and fluorescence spectroscopy. The 2-borylazobenzenes emitted an intense green, yellow, and orange fluorescence, in marked contrast to the usual azobenzene fluorescence. The 4'-siloxy derivative showed the highest fluorescence quantum yield (0.90) among those reported for azobenzenes to date. The correlation between the substituent and the fluorescence properties was elucidated by studying the effect of the substituent on the relaxation process and from DFT and TD-DFT calculations. An electron-donating group at the 4'-position was found to be important for an intense emission. Application of fluorescent azobenzenes as a fluorescent vital stain for the visualization of living tissues was also investigated by microinjection into Xenopus embryos, suggesting these compounds are nontoxic towards embryos.

Photoisomerization of a catecholborane bearing a 2-(phenylazo)phenyl group with an N-B dative bond caused photoswitching of the coordination number of boron between 3 and 4. The Lewis acidity of the catecholborane was switched by photoirradiation, and the complexation ability of the (E)- and the (Z)-isomers of the catecholborane with pyridine differs by more than a factor of 300. [reaction: see text]

N-Aryl, N-alkyl, N-alkoxy, and N-amino derivatives of 2-[bis(pentafluorophenyl)boryl]benzylideneamine were synthesized by the condensation reactions of 2-[bis(pentafluorophenyl)boryl]benzaldehyde with the corresponding amines. Their structures were investigated by NMR and X-ray crystallographic analysis. Their properties were investigated by UV-vis and fluorescence spectroscopy. The boryl-substituted N-arylimines show blue or green fluorescence in hexane at room temperature, and their fluorescence efficiency is much higher than that of N-benzylideneaniline. In particular, the boryl-substituted N-(4-dimethylaminophenyl)imine showed strong green emissions with at least 7000 times higher fluorescence quantum yield (0.73) compared with that of N-benzylideneaniline. The boryl-substituted N-(1-indolyl)- and N-(9-carbazolyl)imines showed dual emissions, one of which was assignable as arising from the lowest singlet excited state and the other from the local excited state of the substituent on the imine nitrogen. The fluorescent properties of the boryl-substituted N-butyl- and N-methoxyimines were also investigated. Reactions of the N-arylimine derivatives with cyanide ion gave the corresponding cyanide adducts and quenched the fluorescence, indicating that these 2-[bis(pentafluorophenyl)boryl]benzylideneamine derivatives have a potential as a cyanide ion sensor.

Azobenzenes are constituents of the commonly and widely used azo dyes. Many dyes, except for the azo dyes, have been utilized for fluorescent materials. However, there are only a few fluorescent azobenzene derivatives and their fluorescence efficiencies are quite low. The current perspective provides an account of the fluorescent azobenzenes and aromatic aldimines featuring an N-B interaction. Incorporation of the intramolecular N-B interaction by using the bis(pentafluorophenyl)boryl group makes the azobenzenes and aromatic aldimines fluorescent with a range of colours. Some of them fluoresce with extraordinarily high fluorescence quantum yields. Their synthesis, structures, fluorescence properties, and applications are discussed.

Enzymes involved in ribosomally synthesized and post-translationally modified peptide (RiPP) biosynthesis often have relaxed specificity profiles and are able to modify diverse substrates. When several such enzymes act together during precursor peptide maturation, a multitude of products can form, and yet usually, the biosynthesis converges on a single natural product. For the most part, the mechanisms controlling the integrity of RiPP assembly remain elusive. Here, we investigate biosynthesis of lactazole A, a model thiopeptide produced by five promiscuous enzymes from a ribosomal precursor peptide.Using our in vitro thiopeptide production (FIT-Laz) system, we determine the order of biosynthetic events at the individual modification level, and supplement this study with substrate scope analysis for participating enzymes. Combined, our results reveal a dynamic thiopeptide assembly process with multiple points of kinetic control, intertwined enzymatic action, and the overall substrate-level cooperation between the enzymes. This work advances our understanding of RiPP biosynthesis processes and facilitates thiopeptide bioengineering..

Alkylsilicates bearing C,O-bidentate ligands could achieve photocatalytic C–H alkylations of heteroarenes under acidic conditions without adding any terminal oxidant.

Silicon can form bonds to other tetracoordinated silicon atoms and these bonds form the framework of many organosilicon compounds and crystalline silicon. Silicon can also form a pentacoordinated anionic structure-a so-called 'silicate'. No compounds containing a direct bond between two silicate moieties-'disilicates' where two silicate structures are combined in one species-have been reported because of the electronic repulsion between the anionic halves and difficulty preventing the release of anions. Here we report the synthesis of thermally stable and isolable disilicates by the reductive coupling reaction of a silane bearing two electron-withdrawing bidentate ligands. Two pentacoordinated silicons, positively charged despite the formal negative charge, constitute a single σ-bond and bind eight negatively charged atoms. They can be reversibly protonated, cleaving two Si-O bonds, to afford a tetracoordinated disilane. Their unique electronic properties could be promising for the construction of functional materials with silicon wire made up of silicate chains.