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The new N,C-chelate boron compounds B(2-phenylazolyl)Mes2 [Mes = mesityl; azolyl = benzothiazolyl (1a), 4-methylthiazolyl (2a), benzoxazolyl (3a), benzimidazolyl (4a)] undergo an unprecedented multistructural transformation upon light irradiation or heating, sequentially producing isomers b, c, d, and e. The dark isomers b generated by photoisomerization of a undergo a rare thermal intramolecular H-atom transfer (HAT), reducing the azole ring and generating new isomers c, which are further transformed into isomers d. Remarkably, isomers d can be converted to their diastereomers e quantitatively by heating, and e can be converted back to d by irradiation at 300 nm. The structures of isomers 1d and 1e were established by X-ray diffraction. The unusual HAT reactivity can be attributed to the geometry of the highly energetic isomers b and the relatively low aromaticity of the azole rings. The boryl unit plays a key role in the reversible interconversion of d and e, as shown by mechanistic pathways established through DFT and TD-DFT calculations. [ABSTRACT FROM AUTHOR]

Four-coordinate organoboron compounds with a π-conjugated chelate backbone have emerged recently as highly attractive materials for a number of applications including use as emitters and electron-transport materials for organic light-emitting diodes (OLEDs) or organic field transistors, photoresponsive materials, and sensory and imaging materials. Many applications of this class of boron compounds stem from the electronic properties of the π-conjugated chelate backbone. Charge-transfer transitions from an aromatic substituent attached to the boron center of the p-conjugated chelate backbone and steric congestion have also been found to play important roles in the luminescent and photochromic properties of the four-coordinate boron compounds. This article provides an update-to-date account on the application aspects of this important class of compounds in materials science with the emphasis on OLED applications and photochromic switching. [ABSTRACT FROM AUTHOR]

N,C-Chelate four-coordinate boron compounds that contain a B(ppy)Mes2unit (ppy = 2-phenylpyridyl, Mes = mesityl) are a new class of photochromic molecules discovered recently by our group that undergo photoisomerization upon exposure to light. To examine the influence of a covalently bound transition metal ion on the photochromic properties of this class of boron compounds, a new molecule (L1) that contains two linearly conjugated ppy units has been synthesized. A BMes2group was attached to L1via chelation with one of the ppy units, producing a new four-coordinate boron compound, B1. The reactions of B1with PtPh2(DMSO)2produced a Pt(II) cyclometalated compound, Pt1, where a PtPh(DMSO) unit is bound to the second ppy unit of B1. Replacement of DMSO in Pt1by p-t-Bu-pyridine provided a new compound, Pt2. A third Pt(II) compound, Pt3, where a Pt(dpm) group (dpm = dipivaloylmethane) is chelated to the second ppy site of B1, was also synthesized successfully. The crystal structures of B1and Pt3have been determined by single-crystal X-ray diffraction analyses. The photophysical and photochromic properties of B1and Pt1–Pt3have been examined. Experimental and computational studies established that Pt(II) cyclometalation to B1stabilizes a 3LC state that involves π→π* transitions localized on the ppy–ppy conjugated backbone. This 3LC state of the Pt(II) compounds is highly phosphorescent, with quantum efficiencies being 0.16, 0.13, and 0.45 for Pt1, Pt2, and Pt3, respectively, in toluene and at ambient temperature. The B(ppy)Mes2chromophore in all three Pt(II) compounds has been found to undergo photoisomerization in a similar manner to that of B1, but with a much lower quantum efficiency than B1. Deactivation of the photoisomerization process by the 3LC state has been found to be most likely responsible for the low photoisomerization quantum efficiency of the Pt(II) compounds. [ABSTRACT FROM AUTHOR]

The impact of two constitutional isomers, 2-(4-BMes2-Ph)-pyridine (p-B-ppy, 1) and 5-Mes2-2-ph0pyridine (p-ppy-B, 2), as N,C-chelate ligands on the structures, stabilities, electronic na dphtophysical properties, and Lewis acidities of Pt(II) complexes has been investigated. SIx Pt(II) complexes, Pt(p-B-ppy)Ph(DMSO) (1a), Pt(p-B-ppy)Ph(py)Ph(py) (1b), [Pt(p-B-ppy)Ph]2(4,4'-bipy) (1c), Pt(p-ppy-B)Ph(DMSO) (2a), Pt(p-ppy-B)Ph(py) (2b), and [Pt(p-ppy-B)Ph]2(4,4'-bipy) (2c), have been synthesized and fully characterized. The structures of 1a, 1c, 2a, and 2c were established by sing;e-crystal X-ray diffraction analysis. All complexes adopt a cis geometry with the phenyk ligand being cis to the phenyl ring of the chelate. The dinuclear complexes 2a and 2c were found to exist in two isomeric forms in solution, syn and anti, with respect to the relative orientation of the two BMes2 groups in the molecule. While all complexes are stable in solution under ambient air, acompound 2a was found to react wtih H2O slowly in solution and form complex 2a-OH, where one of the mesityl groups on the boron center was replaced by an OH group. This instability of 2a is attributed to an internal dimethylsulfoxide-directed hydrolysis process via hydrogen bonds. The electron-accepting ability of the free ligands and the complexes were examined by cyclic voltammetry, establishing that, for p-ppy-B, Pt(II) chelation enhances the elctron-accepting ability while, for p-B-ppy, Pt(II) chelation has little impact. All Pt(II) complexes display oxygen-sensitive phosphorescence in solution at ambient temperature, dominated by B-ppy or ppy-B centered π→π* transitions. The Lewis acidity of the complexes was examined by fluoride titration experiments using UV—vis, phosphorescence, and NMR spectroscopic methods, establishing that the p-ppy-B complexes have similar and strong binding constants while the p-B-ppy complexes have a much lower affinity toward F—, compared to the tree ligands. In the dinuclear complexes, weak electronic communication between the two Pt(II) units is evident in 1c but absent in 2c, attributable to the different steric interactions in the two molecules. [ABSTRACT FROM AUTHOR]

The article focuses on the administration of N,C-Chelate in (2-ph-py)BMes2 and (5-BMes2-2-ph-py)BMes2, which results to the formation of reversible intermolecular C-C bond. It also contributed to the breaking and color switching mediation. Key information on the methodologies and results is further presented.