Structurally Diverse Boron-Nitrogen Heterocycles from an N2O23− Formazanate Ligand

Five new compounds comprised of unprecedented boron-nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N2O23− formazanate ligand with BF3­•OEt2 and NEt3. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox-active heterocycles were characterized using UV-vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography

Optoelectronic Properties of Carbon-Bound Boron Difluoride Hydrazone Dimers

The creation of dimeric boron difluoride complexes of chelating N-donor ligands is a proven strategy for the enhancement of the optoelectronic properties of fluorescent dyes. We report dimers based on the boron difluoride hydrazone (BODIHY) framework, which offer unique and sometimes unexpected substituent-dependent absorption, emission, and electrochemical properties. BODIHY dimers have low-energy absorption bands (lmax = 421 to 479 nm, e = 17,200 to 39,900 M−1 cm−1) that are red-shifted relative to monomeric analogues. THF solutions of these dimers exhibit aggregation-induced emission upon addition of water, with emission enhancement factors ranging from 5 to 18. Thin films of BODIHY dimers are weakly emissive as a result of the inner-filter effect, attributed to intermolecular p-type interactions. BODIHY dimers are redox-active and display two one-electron oxidation and two one-electron reduction waves that strongly depend on the N-aryl substituents. These properties are rationalized using density-functional theory calculations and X-ray crystallography experiments

Oxoborane Formation Turns on Formazanate-Based Photoluminescence

The synthesis of compounds containing multiple bonds to boron has challenged main-group chemists for decades. Despite significant progress, the possibility that the formation of such bonds can turn on photoluminescence has received minimal attention. We report an oxoborane (B=O) complex that is electronically stabilized by a formazanate ligand in the absence of significant steric bulk and, unlike the common BX2 (X = F, Cl) formazanate adducts, exhibits intense photoluminescence. The latter property was rationalized through density-functional calculations which indicated that the B=O bond enhances photoluminescence by drastically reducing differences between the ligand\u27s geometries in the ground and excited states. The title oxoborane compound was synthesized from an air- and moisture-stable BCl2 formazanate complex and subsequently converted to a redox-active boroxine. Each of these species may also serve as a precursor to functional materials

Formazanate Complexes of Hypervalent Group‐14 Elements as Precursors to Electronically Stabilized Radicals

The stability of molecular radicals containing main‐group elements usually hinges on the presence of bulky substituents that shield the reactive radical center. We describe a family of group‐14 formazanate complexes whose chemical reduction allows access to radicals that are stabilized instead by geometric and electron‐delocalization effects, specifically by the square‐pyramidal geometry adopted by the group‐14 atom (Si, Ge, Sn) within the framework of the heteroatom‐rich formazanate ligands. The reduction potentials of the Si, Ge, and Sn complexes as determined by cyclic voltammetry become more negative in that order. Examination of the solid‐state structures of these complexes suggested that their electron‐accepting ability decreases with increasing group‐14 atom size because a larger central atom increases the nonplanarity of the ligand‐based conjugated π‐electron system of the complex. The experimental findings were supported by density‐functional calculations on the parent complexes and the corresponding radicals

Affect - an ethnocentric encounter?: Exploring the 'universalist' imperative of emotional/affectual geographies

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Optoelectronic, Aggregation, and Redox Properties of Double-Rotor Boron Difluoride Hydrazone Dyes

We develop the chemistry of boron difluoride hydrazone dyes (BODIHYs) bearing two aryl substituents and explore their properties. The low-energy absorption bands (λmax = 427–464 nm) of these dyes depend on the nature of the N-aryl groups appended to the BODIHY framework. Electron-donating and extended p-conjugated groups cause a red shift, whereas electron-withdrawing groups result in a blue shift. The title compounds were weakly photoluminescent in solution and strongly photoluminescent as thin films (λPL = 525–578 nm) with quantum yields of up to 18% and lifetimes of 1.1–1.7 ns, consistent with the dominant radiative decay through fluorescence. Addition of water to THF solutions of the BODIHYs studied causes molecular aggregation which restricts intramolecular motion and thereby enhances photoluminescence. The observed photoluminescence of BODIHY thin films is likely facilitated by a similar molecular packing effect. Finally, cyclic voltammetry studies confirmed that BODIHY derivatives bearing para-substituted N-aryl groups could be reversibly oxidized (Eox1 = 0.62–1.02 V vs. Fc/Fc+) to their radical cation forms. Chemical oxidation studies confirmed that para-substituents at the N-aryl groups are required to circumvent radical decomposition pathways. Our findings provide new opportunities and guiding principles for the design of sought-after multifunctional boron difluoride complexes that are photoluminescent in the solid state

An unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the C. elegans putative aminophospholipid translocases

<p>Abstract</p> <p>Background</p> <p>P-type ATPases in subfamily IV are exclusively eukaryotic transmembrane proteins that have been proposed to directly translocate the aminophospholipids phosphatidylserine and phosphatidylethanolamine from the exofacial to the cytofacial monolayer of the plasma membrane. Eukaryotic genomes contain many genes encoding members of this subfamily. At present it is unclear why there are so many genes of this kind per organism or what individual roles these genes perform in organism development.</p> <p>Results</p> <p>We have systematically investigated expression and developmental function of the six, <it>tat-1 </it>through <it>6</it>, subfamily IV P-type ATPase genes encoded in the <it>Caenorhabditis elegans </it>genome. <it>tat-5 </it>is the only ubiquitously-expressed essential gene in the group. <it>tat-6 </it>is a poorly-transcribed recent duplicate of <it>tat-5</it>. <it>tat-2 </it>through <it>4 </it>exhibit tissue-specific developmentally-regulated expression patterns. Strong expression of both <it>tat-2 </it>and <it>tat-4 </it>occurs in the intestine and certain other cells of the alimentary system. The two are also expressed in the uterus, during spermatogenesis and in the fully-formed spermatheca. <it>tat-2 </it>alone is expressed in the pharyngeal gland cells, the excretory system and a few cells of the developing vulva. The expression pattern of <it>tat-3 </it>is almost completely different from those of <it>tat-2 </it>and <it>tat-4</it>. <it>tat-3 </it>expression is detectable in the steroidogenic tissues: the hypodermis and the XXX cells, as well as in most cells of the pharynx (except gland), various tissues of the reproductive system (except uterus and spermatheca) and seam cells. Deletion of <it>tat-1 </it>through <it>4 </it>individually interferes little or not at all with the regular progression of organism growth and development under normal conditions. However, <it>tat-2 </it>through <it>4 </it>become essential for reproductive growth during sterol starvation.</p> <p>Conclusion</p> <p><it>tat-5 </it>likely encodes a housekeeping protein that performs the proposed aminophospholipid translocase function routinely. Although individually dispensable, <it>tat-1 </it>through <it>4 </it>seem to be at most only partly redundant. Expression patterns and the sterol deprivation hypersensitivity deletion phenotype of <it>tat-2 </it>through <it>4 </it>suggest that these genes carry out subtle metabolic functions, such as fine-tuning sterol metabolism in digestive or steroidogenic tissues. These findings uncover an unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the genes encoding the putative aminophospholipid translocases.</p