Recent Advances in the Synthesis of Borinic Acid Derivatives.

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

Boron-Thioketonates: A New Class of S,O-Chelated Boranes as Acceptors in Optoelectronic Devices.

Development of new n-type semiconductors with tunable band gap and dielectric constant has significant implication in dissociating bound charge carrier relevant for demonstrating high performance optoelectronic devices. Boron-ß-thioketonates (MTDKB), analogues to boron-ß-diketonates containing a sulfur atom in the framework of ß-diketones were synthesized. Bulk transport measurement exhibited an outstanding bulk electron mobility of ≈0.003 cm2 V-1 s-1 , which is among the best values reported till date in these class of semiconducting materials and correspondingly a single junction photo responsivity of upto 6 mA W-1 was obtained. This new family of O,S-chelated boron compounds exhibited luminescence in the far red/near-infrared region. The remarkable red shift of 89 nm (fluorescence) observed for 4 a in comparison with analogues boron-ß-diketonate signifies the importance of sulfur in these molecules. MTDKBs with amine functionality have also been investigated as an ON/OFF fluorescent sensor.

Catechol Moiety Integrated Tri-Aryl Type AIEgen for Visual and Quantitative Boronic Acid Detection.

Novel functional AIEgen based on three compact bound aryl skeletons is designed and synthesized. This tri-aryl type luminogen (TA-Catechol) embedded with catechol moiety responds rapidly to series of boronic acids. Real-time visual and quantitative dual-mode detection method is established for the first time with modest precision and low detection limit (8.0 µM). Detailed mechanistic discussion identifies tetra-coordinated boronic species as the key intermediate within sensing procedure. Wide range of organic boronic acids compatible with this strategy is displayed which is promising in high throughput screening technology. Furthermore, solid-state sensing capability of TA-Catechol is also demonstrated.

Synthesis and Strong Solvatochromism of Push-Pull Thienylthiazole Boron Complexes.

The solvatochromic behavior of two donor-π bridge-acceptor (D-π-A) compounds based on the 2-(3-boryl-2-thienyl)thiazole π-linker and indandione acceptor moiety are investigated. DFT/TD-DFT calculations were performed in combination with steady-state absorption and emission measurements, along with electrochemical studies, to elucidate the effect of two different strongly electron-donating hydrazonyl units on the solvatochromic and fluorescence behavior of these compounds. The Lippert-Mataga equation was used to estimate the change in dipole moments (Δµ) between ground and excited states based on the measured spectroscopic properties in solvents of varying polarity with the data being supported by theoretical studies. The two asymmetrical D-π-A molecules feature strong solvatochromic shifts in fluorescence of up to ~4300 cm-1 and a concomitant change of the emission color from yellow to red. These changes were accompanied by an increase in Stokes shift to reach values as large as ~5700-5800 cm-1. Quantum yields of ca. 0.75 could be observed for the N,N-dimethylhydrazonyl derivative in nonpolar solvents, which gradually decreased along with increasing solvent polarity, as opposed to the consistently reduced values obtained for the N,N-diphenylhydrazonyl derivative of up to ca. 0.20 in nonpolar solvents. These two push-pull molecules are contrasted with a structurally similar acceptor-π bridge-acceptor (A-π-A) compound.

Recent Progress on Synthesis of N,N'-Chelate Organoboron Derivatives.

N,N'-chelate organoboron compounds have been successfully applied in bioimaging, organic light-emitting diodes (OLEDs), functional polymer, photocatalyst, electroluminescent (EL) devices, and other science and technology areas. However, the concise and efficient synthetic methods become more and more significant for material science, biomedical research, or other practical science. Here, we summarized the organoboron-N,N'-chelate derivatives and showed the different routes of their syntheses. Traditional methods to synthesize N,N'-chelate organoboron compounds were mainly using bidentate ligand containing nitrogen reacting with trivalent boron reagents. In this review, we described a series of bidentate ligands, such as bipyridine, 2-(pyridin-2-yl)-1H-indole, 2-(5-methyl-1H-pyrrol-2-yl)quinoline, N-(quinolin-8-yl)acetamide, 1,10-phenanthroline, and diketopyrrolopyrrole (DPP).

Recent Advances in π-Conjugated N

Boron-containing π-conjugated materials are archetypical candidates for a variety of molecular scale applications. The incorporation of boron into the π-conjugated frameworks significantly modifies the nature of the parent π-conjugated systems. Several novel boron-bridged π-conjugated materials with intriguing structural, photo-physical and electrochemical properties have been reported over the last few years. In this paper, we review the properties and multi-dimensional applications of the boron-bridged fused-ring π-conjugated systems. We critically highlight the properties of π-conjugated N^C-chelate organoboron materials. This is followed by a discussion on the potential applications of the new materials in opto-electronics (O-E) and other areas. Finally, attempts will be made to predict the future direction/outlook for this class of materials.

The Synthesis of Picolinamide-Supported Tetracoordinated Organoboron Complexes with Aggregation-Induced Emission Property.

The picolinamide-supported tetracoordinated organoboron complexes containing diaryl boronyl segments have been synthesized for the first time. Aryl trifluoroborates were utilized as the BAr2 sources to introduce different aryl motifs with diverse functional groups. The optical experiments discovered these five-membered boron-containing complexes were aggregation-induced emission (AIE) active, thus affording a new class of AIE molecules.

Recognition of Aß oligomer by LilrB2 acceptor: a tetracoordinated zipper mechanism.

Leukocyte immunoglobulin-like receptor B2 (LilrB2) is one of discovered cell surface ß-amyloid (Aß) receptors and taken as a promising therapeutic target for the treatment of Alzheimer's disease (AD). Aß42 oligomer rather than monomer is toxic to neuronal cells and can directly bind to LilrB2, resulting in synaptic loss and cognitive impairment in the development of AD. Therefore, uncovering the mechanism of interaction between Aß42 oligomer and LilrB2 becomes the first step to obtain a clear drug target and specific binding sites. Herein, a tetracoordinated mechanism for the Aß oligomer-LilrB2 binding was first put forward by employing Aß42 dimer mimic-antiparallel copies of Aß42 core fragment 16KLVFFA21, to bind LilrB2 as models, in which four key residues (F5/F6/L12/F14) in the Aß42 mimic are bound strongly with LilrB2 residue(s) or accommodated by four hydrophobic cavities in LilrB2 to generate a stable complex. Bi-dentate binding, however, cannot keep the complex Aß42 mimic-LilrB2 stable. The inhibitor fluspirilene can disturb the binding of four key residues of Aß42 to LilrB2, justifying the tetracoordinated zipper mechanism on the other hand.

Difluoroboron-Enabled Thermally Activated Delayed Fluorescence.

A new series of tetracoordinated boron-enabled thermally activated delayed fluorescence (TADF) materials with a donor-acceptor BF2-type framework were designed and conveniently synthesized. Difluoroboron plays a critical role and acts as a key to coordinate with the latent acceptor of the 2-(4-phenylpyridin-2-yl)phenol (PPyPOH) moiety to realize TADF. TADF materials are air-stable and have a high photoluminescence quantum yield of up to 99%. NOBF2-Cz- and NOBF2-DPCz-doped blue OLEDs demonstrated EQEs of 11.0% with CIE coordinates of (0.14, 0.16) and 15.8% with (0.14, 0.28) and high brightness of 6761 and 19383 cd/m2 could be achieved, respectively. Moreover, the blue OLED doped with NOBF2-DPCz and the green OLED doped with NOBF2-DMAC achieved operational lifetimes at 50% of initial luminance (L0 = 500 cd/m2), LT50, of 54 and 920 h, respectively. This work indicates that these tetracoordinated difluoroboron molecules can act as efficient and stable TADF materials for OLED applications.