Dodecaborate anions of the type B12X122- and B12X11Y2- (X=H, Cl, Br, I and Y=OH, SH, NH3+, NR3+) form strong (Ka up to 106Lmol-1, for B12Br122-) inclusion complexes with gamma-cyclodextrin ...(gamma-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to -25kcalmol-1) and entropies (TDeltaS up to -18.4kcalmol-1, both for B12I122-), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous solution. In line with this argument, salting-in effects revealed dodecaborates as superchaotropic dianions.
Boron-doping has long been recognized as a promising LUMO energy-lowering modification of graphene and related polycyclic aromatic hydrocarbons (PAHs). Unfortunately, synthetic difficulties have been ...a significant bottleneck for the understanding, optimization, and application of precisely boron-doped PAHs for optoelectronic purposes. Herein, a facile one-pot hydroboration electrophilic borylation cascade/dehydrogenation approach from simple alkene precursors is coupled with postsynthetic B-substitution to give access to ten ambient-stable core- and periphery-tuned boron-doped PAHs. These include large hitherto unknown doubly boron-doped analogues of anthanthrene and triangulene. Crystallographic, optical, electrochemical, and computational studies were performed to clarify the effect of boron-doped PAH shape, size, and structure on optoelectronic properties. Our molecular tuning allowed the synthesis of molecules exhibiting visible-range absorption, near-unity fluorescence quantum yields, and, to our knowledge, the most facile electrochemical reductions of any reported ambient-stable boron-doped PAHs (corresponding to LUMO energy levels as low as fullerenes). Finally, our study describes the first implementation of a precise three-coordinate boron-substituted PAH as an acceptor material in organic solar cells with power conversion efficiencies (PCEs) of up to 3%.
Yapı elemanları için en önemli durabilite özelliklerinden birisi de yüksek sıcaklık etkisine maruz kaldıktan sonra göstermiş oldukları dayanımdır. Bu çalışmada, öğütülmüş yüksek fırın cürufu (İÖYFC), ...bazalt (BZ) ve üleksit (U) katkılarıyla üretilen beton örneklerin yüksek sıcaklık etkisi altındaki özellikleri araştırılmıştır. Bu amaçla, TS 802 standardında belirtilen şartlara uygun beton karışımında ince agreganın yerine kütlece yüksek fırın cürufu %10-20, bazalt %10-20 ve üleksit %1-2 oranlarında eklenmiştir. Yüksek fırın cürufu, bazalt ve üleksit katkılı 7 ve 28 günlük örnekler bir saat 600 ve 800 °C sıcaklık etkisinde bırakılarak havada ve suda olmak üzere iki farklı soğutma rejimine tabi tutulmuştur. Yüksek sıcaklığa maruz bırakılan örneklere basınç dayanımı ve ultrasonik dalga hızı deneyleri yapılmıştır. Ayrıca örnekler üzerinde 7 ve 28 günlük basınç dayanımı, ultrases geçiş hızı ve aşınma deneyleri yapılmıştır. 600 °C yüksek sıcaklık etkisine maruz bırakılan numunelerin havada soğutma sonrası basınç dayanım değerleri referans numunesine göre %40-%20-%8 oranlarında ve suda soğutma sonrası basınç dayanım değerleri referans numunesine göre %60-%55-%42 oranlarında İÖYFC10, İÖYFC20 ve U1 katkısının yüksek sıcaklık etkisine karşı dayanım değerlerini arttırdığı göstermektedir. Bu değerlendirme ile yüksek fırın cürufu ve üleksit katkısının ince agrega olarak beton karışımında yüksek sıcaklık etkilerine karşı dayanıklı beton üretiminde kullanılabileceğini göstermiştir.Anahtar Kelimeler: Bazalt, Yüksek fırın cürufu, Durabilite, Yüksek sıcaklık
Differential electrochemical mass spectrometry (DEMS) analysis of the oxygen isotopologues produced by 18O-labeled Co-OEC in H2 16O reveals that water splitting catalysis proceeds by a mechanism that ...involves direct coupling between oxygens bound to dicobalt edge sites of Co-OEC. The edge site chemistry of Co-OEC has been probed by using a dinuclear cobalt complex. 17O NMR spectroscopy shows that ligand exchange of OH/OH2 at Co(III) edge sites is slow, which is also confirmed by DEMS experiments of Co-OEC. In borate (Bi) and phosphate (Pi) buffers, anions must be displaced to allow water to access the edge sites for an O–O bond coupling to occur. Anion exchange in Pi is slow, taking days to equilibrate at room temperature. Conversely, anion exchange in Bi is rapid (k assoc = 13.1 ± 0.4 M–1 s–1 at 25 °C), enabled by facile changes in boron coordination. These results are consistent with the OER activity of Co-OEC in Bi and Pi. The Pi binding kinetics are too slow to establish a pre-equilibrium sufficiently fast to influence the oxygen evolution reaction (OER), consistent with the zero-order dependence of Pi on the OER current density; in contrast, Bi exchange is sufficiently facile such that Bi has an inhibitory effect on OER. These complementary studies on Co-OEC and the dicobalt edge site mimic allow for a direct connection, at a molecular level, to be made between the mechanisms of heterogeneous and homogeneous OER.
Carbon dots (CDs) have attracted attention in metal‐free afterglow materials, but most CDs were heteroatom‐containing and the afterglow emissions are still limited to the short‐wavelength region. A ...universal approach to activate the room‐temperature phosphorescence (RTP) of both heteroatom‐free and heteroatom‐containing CDs was developed by one‐step heat treatment of CDs and boric acid (BA). The introduction of an electron‐withdrawing boron atom in composites can greatly reduce the energy gap between the singlet and triplet state; the formed glassy state can effectively protect the excited triplet states of CDs from nonradiative deactivation. A universal host for embedding CDs to achieve long‐lifetime and multi‐color (blue, green, green‐yellow and orange) RTP via a low cost, quick and facile process was developed. Based on their distinctive RTP performances, the applications of these CD‐based RTP materials in information encryption and decryption are also proposed and demonstrated.
The room‐temperature phosphorescence (RTP) of CDs was activated by one‐step heat treatment of CDs and boric acid (BA). Heteroatom‐free CDs (a‐CDs) possess favorable RTP in BA matrix with a lifetime as high as 1.6 s. Blue, green, yellow‐green, and orange RTP CD‐based materials were obtained. These CD‐based RTP materials were successfully applied in information encryption owing to their distinctive RTP performance.
Deep‐ultraviolet nonlinear optical (DUV NLO) crystals are the key materials to extend the output range of solid‐state lasers to below 200 nm. The only practical material KBe2BO3F2 suffers high ...toxicity through beryllium and strong layered growth. Herein, we propose a beryllium‐free material design and synthesis strategy for DUV NLO materials. Introducing the (BO3F)4−, (BO2F2)3−, and (BOF3)2− groups in borates could break through the fixed 3D B–O network that would produce a larger birefringence without layering and simultaneously keep a short cutoff edge down to DUV. The theoretical and experimental studies on a series of fluorooxoborates confirm this strategy. Li2B6O9F2 is identified as a DUV NLO material with a large second harmonic generation efficiency (0.9×KDP) and a large predicted birefringence (0.07) without layering. This study provides a feasible way to break down the DUV wall for NLO materials.
Be gone: A strategy to prepare a beryllium‐free material that does not grow in layers for deep‐UV (DUV) nonlinear optical (NLO) materials is developed and carried out. Introducing the (BO3F)4−, (BO2F2)3−, and (BOF3)2− groups in borates is a feasible way to balance the criteria of deep‐UV NLO materials, breaking down the DUV wall for NLO materials.
Bottom-up synthesis of graphene nanoribbons (GNRs) has significantly advanced during the past decade, providing various GNR structures with tunable properties. The synthesis of chiral GNRs, however, ...has been underexplored and only limited to (3,1)-GNRs. We report herein the surface-assisted synthesis of the first heteroatom-doped chiral (4,1)-GNRs from the rationally designed precursor 6,16-dibromo-9,10,19,20-tetraoxa-9a,19a-diboratetrabenzoa,f,j,operylene. The structure of the chiral GNRs has been verified by scanning tunneling microscopy, noncontact atomic force microscopy, and Raman spectroscopy in combination with theoretical modeling. Due to the presence of oxygen–boron–oxygen (OBO) segments on the edges, lateral self-assembly of the GNRs has been observed, realizing well-aligned GNR arrays with different modes of homochiral and heterochiral inter-ribbon assemblies.
Unsymmetric 1,1-diboryl alkenes bearing one −BPin (BPin = pinacolatoboryl) and one −BDan (BDan = 1,8-diaminonaphthalatoboryl) substituent each were hydrogenated in high yield and enantioselectivity ...using C 1-symmetric pyridine(diimine) (PDI) cobalt complexes. High activities and stereoselectivities were observed with an array of 2-alkyl-, 2-aryl-, and 2-boryl-substituted 1,1-diboryl alkenes, giving rise to enantioenriched diborylalkane building blocks. Systematic study of substrate substituent effects identified competing steric and electronic demands in the key activating role of the boron substituents, whereby sterically unencumbered boronates such as −BDan, −BCat (BCat = catecholatoboryl), and −Beg (Beg = ethylene glycolatoboryl) promote the hydrogenation of trisubstituted alkenes by enabling irreversible α-boron-directed insertion pathways to achieve otherwise challenging hydrogenations of trisubstituted alkenes. Deuterium-labeling studies with 1,1-diboryl alkenes support an insertion pathway generating a chiral intermediate with two different boron substituents and cobalt bound to the same carbon.
Conventional theory predicts that ultrahigh lattice thermal conductivity can only occur in crystals composed of strongly bonded light elements, and that it is limited by anharmonic three-phonon ...processes. We report experimental evidence that departs from these long-held criteria. We measured a local room-temperature thermal conductivity exceeding 1000 watts per meter-kelvin and an average bulk value reaching 900 watts per meter-kelvin in bulk boron arsenide (BAs) crystals, where boron and arsenic are light and heavy elements, respectively. The high values are consistent with a proposal for phonon-band engineering and can only be explained by higher-order phonon processes. These findings yield insight into the physics of heat conduction in solids and show BAs to be the only known semiconductor with ultrahigh thermal conductivity.
The key parameters of conjugated polymers are lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Few approaches can simultaneously lower LUMO and ...HOMO energy levels of conjugated polymers to a large extent (>0.5 eV). Disclosed herein is a novel strategy to decrease both LUMO and HOMO energy levels of conjugated polymers by about 0.6 eV through replacement of a CC unit by a B←N unit. The replacement makes the resulting polymer transform from an electron donor into an electron acceptor, and is proven by fluorescence quenching experiments and the photovoltaic response. This work not only provides an effective approach to tune the LUMO/HOMO energy levels of conjugated polymers, but also uses organic boron chemistry as a new toolbox to develop conjugated polymers with high electron affinity for polymer optoelectronic devices.
Transforming units: A novel strategy decreases both LUMO and HOMO energy levels of conjugated polymers, by about 0.6 eV, through replacement of a CC unit by a B←N unit. The replacement transforms the resulting polymer from an electron donor into an electron acceptor.
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