位阻型有机电致磷光材料的研究进展

重金属旋轨耦合作用使磷光有机发光二极管的内量子效率在理论上可达100%,突破了传统有机荧光二极管内量子效率为25%的限制,是目前最有潜力的第三代显示器.但是,磷光材料常因浓度猝灭、三线态湮灭、二聚体发光等因素影响器件性能.位阻型磷光材料能够抑制分子间的强相互作用,从而解决了上述问题.本文作者综述了近年来具有大体积空间位阻效应的铱(III)、铂(II)、锇(II)等有机小分子磷光材料的研究进展,讨论了其目前存在的问题和未来的发展趋势.     

The effect of the steric hindrance on metallic cation conduction in polymer electrolytes

2,6-Di-t-butylphenol and oligo(ethylene oxide) bound covalently to polyisocyanate were synthesized and characterized. The ionic conductivities of their Li, Na, and K phenolates were studied at various temperatures. The conductivities were in the range of 10^?7?10^?5 S/cm at 30°C. The conductivity of Na and K salts was approximately 10² greater than that of the Li salts. The t-butyl groups serve to dissociate K and Na ions from the phenoxide. The cations, therefore, are more mobile as a result increasing the conductivity. The temperature dependence of ionic conductivity suggests that the migration of ions is controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel–Tammann–Fulchere plots. The polyisocyanate backbone is a rather stiff structure, however, a flexible oligo(ethylene oxide) side chain forms complexes with metal ion. Since the ion transport is associated with the local movement of polymer segments, the rigidity of the polymer backbone does not have much influence on the ion mobility.     

有机空间位阻剂对NaP分子筛的调控作用

以粉煤灰中提取出的硅酸钠和铝酸钠为原料,通过水热合成法制备NaP型分子筛。通过正交实验优化了晶化时间、晶化温度和溶液硅水比等工艺参数,提出了通过空间位阻效应调控晶粒生长过程的方法,探索了结构空间位阻作用对NaP型分子筛生长过程晶型、粒径的调控规律。采用XRD、FI-IR、SEM、BET等手段对产物的晶型、粒径和形貌进行表征,并对不同条件下制备的NaP型分子筛的吸附性能进行了评价。结果表明,水热反应体系中引入空间位阻效应能有效调控Na P型分子筛的形貌和粒径;空间位阻效应的影响规律为环状结构链状结构,长链结构短链结构。吸附性能测试表明,Zn~(2+)有效吸附去除率可达99.8%。     

Topology control of three-dimensional covalent organic frameworks by adjusting steric hindrance effect

Since the intrinsic topological network determines their pore characteristics and functional applications, it is important to construct 3D COFs with target topology from predesigned functional building blocks. However, when starting from precursors with same connectivity but different bulky groups, the structure and topology of 3D COFs may change, which will greatly increase the complexity of the crystal structure determination. Therefore, it is essential to understand how to control the steric ...     

A SHG-active manganese coordination polymer with noncentrosymmetric structure based on achiral carboxyphosphinate ligand

The hydrothermal reaction of MnSO₄ with the achiral 2-carboxyethyl(phenyl)phosphinate ligand (H₂L) afforded a 2?D coordination polymer manganese phosphinate, [Mn(HL)₂]_n (1) (H₂L?=?2-carboxyethyl(phenyl) phosphinic acid). It contains two types of dimeric ring motifs, which can generate a layer structure through edge-sharing. The interlayer stacking by C-H…π interactions between the C-H groups of the phenyl rings of HL^- and the phenyl rings of the adjacent layers results in its crystallization in a noncentrosymmetric crystal structure with (4³)₂(4⁶·6⁶·8³) topology. Compound 1 shows a second harmonic generation response that is 0.8 times that of urea. The luminescence spectrum indicates an emission maximum at 457?nm, attributed to an intra-ligand emission state.     

Assembly of the highest connectivity Wells-Dawson polyoxometalate coordination polymer: the use of organic ligand flexibility

Through tuning the length of flexible bis(triazole) ligands and different metal ion coordination geometries, four Wells-Dawson polyoxoanion-based hybrid compounds, [Cu 6(btp) 3(P 2W 18O 62)].3H 2O ( 1) (btp = 1,3-bis(1,2,4-triazol-1-y1)propane), [Cu 6(btb) 3((P 2W 18O 62)].2H 2O ( 2), [Cu 3(btb) 6(P 2W 18O 62)].6H 2O (btb = 1,4-bis(1,2,4-triazol-1-y1)butane) ( 3), and [Cu 3(btx) 5.5((P 2W 18O 62)].4H 2O (btx = 1,6-bis(1,2,4-triazol-1-y1)hexane) ( 4), were synthesized and structurally characterized. In compound 1, the metal-organic motif exhibits a ladder-like chain, which is further fused by the ennead-dentate [P 2W 18O 62] (6-) anions to construct a 3D structure. In compound 2, the metal-organic motif exhibits an interesting Cu-btb grid layer, and the ennead-dentate polyoxoanions are sandwiched by two Cu-btb layers to construct a 3D structure. Compound 3 exhibits a (4 (2).6 (2).8 (2)) 3D Cu-btb framework with square and hexagonal channels arranged alternately. The hexa-dentate polyoxoanions incorporate only into the hexagonal channels. In compound 4, there exist two sets of (6 (1).10 (2)) 2(6 (1).8 (2).10 (3)) 3D Cu-btx frameworks to generate a 2-fold interpenetrated structure into which the penta-dentate polyoxoanions are inserted to construct a 3D structure. The structural analyses reveal that the length of flexible bis(triazole) ligands and metal ion coordination geometries have a synergic influence on the structures of this series. To our knowledge, they have the highest connectivity for the Wells-Dawson polyoxometalate coordination polymers to date.     

Influence of small additions of polar organic liquids on the energy stability of the steric structure of water

Belorussian State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 146–148, July–August, 1992.     

Na_4-CyDTA空间位阻的动态核磁共振研究

用动态核磁共振(DNMR)的方法研究了Na4CyDTA乙羧基质子1H NMR谱随温度的变化关系,结果表明,常温下由于乙羧基旋转受到空间阻碍导致其1H NMR谱分裂为1组AB谱,随温度升高,AB谱的化学位移差减小.通过拟和化学位移差与温度的关系,计算出了Na4CyDTA中阻碍乙羧基旋转的能垒为16.95 kJ/mol.     

Na4-CyDTA空间位阻的动态核磁共振研究

用动态核磁共振（DNMR）的方法研究了Na4-CyDTA乙羧基质子^1H—NMR谱随温度的变化关系，结果表明，常温下由于乙羧基旋转受到空间阻碍导致其^1H—NMR谱分裂为1组AB谱，随温度升高，AB谱的化学位移差减小．通过拟和化学位移差与温度的关系，计算出了Na4-CyDTA中阻碍乙羧基旋转的能垒为16．95kJ／mol．     

Influence of steric hindrance on the core geometry and sulfoxidation chemistry of carboxylate-rich diiron(II) complexes

The asymmetric terphenyl-2'-carboxylate ligand 3,5-dimethyl-1,1':3',1' '-terphenyl-2'-carboxylate, -O2CArPh,Xyl, was prepared in high yield. This ligand facilitates the assembly of the diiron(II) complexes [Fe2(micro-O2CArTol)2(O2CArPh,Xyl)2(THF)2] [2, -O2CArTol=2,6-di-p-tolylbenzoate], [Fe2(micro-O2CArTol)2(O2CArPh,Xyl)2(pyridine)2] (5), [Fe2(micro-O2CArPh,Xyl)2-(O2CArPh,Xyl)2(THF)2] (3), and [Fe2(micro-O2CArPh,Xyl)2(O2CArPh,Xyl)2(pyridine)2] (6), all of which have a windmill geometry. The iron-iron distance of 3.355[10] A in 6 is approximately 1 A shorter than that in the analogue [Fe2(micro-O2CArTol)2(O2CArTol)2(pyridine)2] (4) and similar to the approximately 3.3 A metal-metal separation at the active site of the reduced diiron(II) form of the soluble methane monooxygenase hydroxylase enzyme (MMOHred). A series of ortho-substituted picolyl-based ligands, 2-picSMe, 2-picSEt, 2-picStBu, 2-picSPh, 2-picSPh(Me3) (Ph(Me3)=mesityl), and 2-picSPh(iPr3) (Ph(iPr3)=2,4,6-triisopropylphenyl), were prepared and allowed to react with [Fe2(micro-O2CAr)2(O2CAr)2(THF)2] to produce [Fe2(micro-O2CAr)3(O2CAr)(picSR)] (7-13, Ar=ArTol or ArPh,Xyl) complexes in 45-87% yields. The substrates tethered to the pyridine N-donor ligands picSR, where R=Me, Et, tBu, or Ph, coordinate to one iron atom of the diiron(II) center by the nitrogen and sulfur atoms to form a five-membered chelate ring. The Fe-S distance be-comes elongated with increasing steric hindrance imparted by the R group. The most sterically hindered ligands, 2-picSPh(Me3) and 2-picSPh(iPr3), bind to the metal only through the pyridine nitrogen atom. The reactions of several of these complexes with dioxygen were investigated, and the oxygenated products were analyzed by 1H NMR spectroscopy and GC/MS measurements following decomposition on a Chelex resin. The amount of sulfoxidation product is correlated with the Fe...S distance. The ratio of oxidized to unoxidized thioether substrate varies from 3.5, obtained upon oxygenation of the weakly coordinated 2-picSPh ligand in 10, to 1.0, obtained for the bulky 2-picSPh(iPr3) ligand in 12, for which the iron-sulfur distance is >4 A. External thioether substrates were not oxidized when present in oxygenated solutions of paddlewheel and windmill diiron(II) complexes containing 1-methylimidazole or pyridine ligands, respectively.     

Influence of hydrogen bonding on coordination polymer assembly

An extended dipyridyl ligand (L1) capable of hydrogen bonding with guest species via urea functionalities has been designed and synthesised. Assembly of a silver(I) coordination polymer of L1 is dependent on the nature of the hydrogen bond acceptor in a logical extension of the monopyridyl analogue.     

Improving the yield of mono-DNA-functionalized gold nanoparticles through dual steric hindrance

A novel strategy of dual steric hindrance, which was obtained by Janus modification of gold nanoparticles (Au NPs) and volume exclusion of DNA, was adopted to prepare mono-DNA-modified Au NPs. The yield of mono-DNA-functionalized Au NPs significantly improved from 44 to 70% in the reaction between Au NPs and thiolated DNA. Furthermore, the specificity of mono-DNA-functionalized Au NPs was enhanced from 57 to 95%. The as-prepared Au NPs without postsynthetic treatment showed good controllability in self-assembly fabrication of complex nanostructures.     

Synthesis and characterization of the mixed ligand coordination polymer CPO-5

The synthesis and crystal structures of a novel coordination polymer and its high-temperature variant are described. The as-synthesized material (CPO-5-as), of composition Zn(4,4′-bipyridine)(4,4′-biphenyldicarboxylate)·3H₂O, crystallizes in the triclinic space group P-1 (No. 2) with a=11.0197(2), b=14.2975(3), c=7.6586(1) Å, α=95.9760(9)°, β=108.026(1)°, γ=91.373(1)° and V=1139.16(4) Å³. CPO-5-as is composed of tetrahedral zinc centers that are connected by the organic linkers to give five independent, interpenetrating diamond networks. In the structure, there is additional space for channels that are filled with three water molecules. These water molecules can be removed, leading to an anhydrous variant at 130^oC. CPO-5-130, of composition Zn(4,4′-bipyridine)(4,4′-biphenyldicarboxylate), crystallizes in the triclinic space group P-1 (No. 2) with a=11.1844(6), b=14.0497(7), c=7.7198(3) Å, α=96.917(2)°, β=109.527(2)°, γ=89.115(3)° and V=1134.6(1) Å³. The structure of the five interpenetrating networks is virtually unchanged after the dehydration resulting in CPO-5-130 being a porous structure with an estimated free volume of 19.8%.     

Influence of steric hindrance on enantioseparation of Dns-amino acids and pesticides on terguride based chiral selectors in capillary electrophoresis

Three urea derivatives of ergoline-based chiral selectors (CSs), differing in the size of the urea side chain, i.e. dimethyl- (CSI), diethyl- (CSII), and diisopropylurea (CSIII), were used to study the effect of steric hindrance on the enantioseparation of dansyl amino acids (Dns-AAs), pesticides, and mandelic acid under condition of capillary electrophoresis (CE) in linear polyacrylamide coated capillaries. A mixture of organic modifiers (MeOH/THF, 4:1 v/v) in a BGE consisting of 100 mM beta-alanine-acetate was used to increase the solubility of CSs up to 25 mM. The capillary was filled with CS (high UV absorption), and the inlet and outlet vials contained buffer solutions only. The best enantioseparation of Dns-AAs was achieved on CSI. Increased steric hindrance of the chiral binding site led to reduction of both enantioselectivity and resolution. The opposite pattern was observed for the separation of mandelic acid enantiomers, where the best enantioseparation and resolution was obtained with CSIII. Most of the pesticides studied reached maximum selectivity on the diethylurea ergoline derivative (CSII). Enantioseparation of fenoxaprop was found to be independent of steric hindrance.     

Polyoxometalate steric hindrance driven chirality-selective separation of subnanometer carbon nanotubes

Subnanometer single-chirality single-walled carbon nanotubes (SWCNTs) are of particular interest in multiple applications. Inspired by the interdisciplinary combination of redox active polyoxometalates and SWCNTs, here we report a cluster steric hindrance strategy by assembling polyoxometalates on the outer surface of subnanometer SWCNTs via electron transfer and demonstrate the selective separation of monochiral (6,5) SWCNTs with a diameter of 0.75 nm by a commercially available conjugated polymer. The combined use of DFT calculations, TEM, and XPS unveils the mechanism that selective separation is associated with tube diameter-dependent interactions between the tube and clusters. Sonication drives the preferential detachment of polyoxometalate clusters from small-diameter (6,5) SWCNTs, attributable to weak tube–cluster interactions, which enables the polymer wrapping and separation of the released SWCNTs, while strong binding clusters with large-diameter SWCNTs provide steric hindrance and block the polymer wrapping. The polyoxometalate-assisted modulation, which can be rationally customized, provides a universal and robust pathway for the separation of SWCNTs.

We develop a cluster steric hindrance strategy by assembling polyoxometalates on subnanometer single-walled carbon nanotubes (SWCNTs) and demonstrate the selective separation of single-chirality (6,5) SWCNTs via polymer extraction.