Fluorinated diphenylpolyenes: crystal structures and emission properties

(E,E,E)-1,6-Diaryl(Ar)-1,3,5-hexatrienes (2, Ar = 4-fluorophenyl; 3, Ar = 2,4-difluorophenyl; 4, Ar = 2,4,6-trifluorophenyl; 5, Ar = perfluorophenyl) and (E,E,E)-1-perfluorophenyl-6-phenyl-1,3,5-hexatriene (6) were prepared. The absorption and fluorescence spectra in methylcyclohexane solution showed only a small dependence on the fluorine ring substituent, and were similar to those of the unsubstituted parent compound (1, Ar = phenyl). The solid-state absorption and fluorescence spectra shifted to red relative to those in solution and strongly depended on the substituent. The emission from crystals 1-5 originated mainly from monomeric species with the maximum wavelength (lambda f(max)) of 440-465 nm, which overlapped the emission from molecular aggregates (1-4) or excimeric species (5) in the red region. Crystal 6 exhibited red-shifted (lambda f(max) = 530 nm) and structureless emission due to excimers. The cocrystal of 1 and 5 (1/5) showed red-shifted (lambda f(max) = 558 nm) and distinctly structured emission, not from exciplexes but from the excited states of molecular aggregates in which molecules 1 and 5 strongly interact already in the ground state. These assignments were confirmed by the results of fluorescence lifetime and quantum yield measurements in the solid state. Single-crystal X-ray structure analyses showed that the molecules were basically planar in each crystal, whereas the crystal packing was strongly substituent-dependent. Weak pi-pi interactions in the herringbone (1 and 2) and in the pi-stacked but largely offset structures (3 and 4) account for their predominantly monomeric origin of emission. The observation of excimer fluorescence from 5 was rather unexpected, since the molecules in this crystal were arranged in an offset stacking fashion due to perfluorophenyl-perfluorophenyl (C6F5...C6F5) interaction. The structures of 6 and 1/5 considerably resembled each other, in which molecules were pi-stacked with more face-to-face geometries than those in 5, as a result of strongly attractive perfluorophenyl-phenyl (C6F5...C6H5) interaction. Nevertheless, the fluorescence origin was clearly different for 6 and 1/5. This can be ascribed to the difference in the strength of orbital-orbital interaction between molecular pi-planes in the ground and excited states in crystals.     

Synthesis, mesomorphic properties and crystal structure studies of a chiral ferroelectric liquid crystal series

A new series of chiral mesogens: (R) 4-(1-methylheptyloxycarbonyl)phenyl 4-(4-alkyloxyphenyl)ethylylbenzoates has been synthesized. All materials are mesomorphic and the liquid crystalline properties were characterized by optical observation, DSC and electro-optical measurements. They display SmA and ferroelectric SmC* phases at low temperatures. One of them, the nonyloxy derivative, exhibits the SmC*alpha phase, present in different 'antiferroelectric' series. This behaviour is confirmed by mixture studies. Furthermore one compound of the series, the heptyloxy derivative, C37H48O5 crystallizes in the P21 space group (Z=2) with the following parameters: a=8.497 (1), b=5.490 (1), c=36.148 (4)A with beta 92.72 (1) . The final R and wR reliability factors were equal to 0.109 and 0.124, respectively; the goodness of fit was equal to 3.0. The whole molecule is L-shaped with the long chiral chain almost perpendicular to the core moiety as observed for several compounds showing an antiferroelectric mesophase. In the crystal, the molecules related through the 2 1 axis, located at z=0.5, give an antiparallel smectic C-like arrangement. The thickness of the sheets is equal to the c parameter, with a tilt angle close to 35 . There are strong intersheet interactions between the chiral chains related through the 2 1 axes located at z=0 and 1.     

A combined spectroscopic and theoretical study of a series of conformationally restricted hexapeptides carrying a rigid binaphthyl-nitroxide donor-acceptor pair

The structural features of a series of linear hexapeptides of general formula Boc‐B‐A_r‐T‐A_m‐OtBu, where A is L ‐Ala or Aib (α‐aminoisobutyric acid), B is (R)‐Bin, a binaphthyl‐based C^α,α‐disubstituted Gly residue, T is Toac, a nitroxide spin‐labeled C^α,α‐disubstituted Gly, and r+m=4, were investigated in methanol solution by fluorescence, transient absorption, IR and CD spectroscopic studies, and by molecular mechanics calculations. These peptides are denoted as B‐T/r‐m, to emphasize the different position of Toac with respect to that of the Bin fluorophore in the amino acid sequence. The rigidity of the B‐T donor–acceptor pair and of the Aib‐rich backbone allowed us to investigate the influence of the interchromophoric distance and orientation on the photophysics of the peptides examined. The excited state relaxation processes of binaphthyl were investigated by time‐resolved fluorescence and transient absorption experiments. Dynamic quenching of the excited singlet state of binaphthyl by Toac was successfully interpreted by the Förster energy transfer model, provided that the mutual orientation of the chromophores is taken into account. This implies that interconversion among conformational substates, which involves puckering of the Toac piperidine ring, is slow on the time scale of the transfer process, that is slower than 5 ns. By comparison of the experimental and theoretical data, the type of secondary structure (right‐handed 3₁₀ helix) from the B‐T/r‐m peptides in solution was determined; this would not have been achievable by using the CD and NMR data only, as the data are not diagnostic in this case. Static quenching was observed in all peptides examined but B‐T/1‐3, where the effect can be ascribed to a non‐fluorescent complex. Among the computed low‐energy conformers of these peptides, there is one structure exhibiting a NO ^. –naphthalene center‐to‐center distance <6 Å, which might be assigned to this complex. The overall results emphasize the versatility of fluorescence experiments in 3D‐structural studies in solution.     

The synthesis, crystal structure and spectroscopic properties of luminescent Zn(II) complex

A luminescent Zn(II) complex 1, ZnL2Cl2.2H2O has been synthesized where L=2,2',2'-(1,3,5-benzenetriyltrimethylidyne) as a yellow crystal. Single crystal X-ray analysis of the compound 1 shows a distorted tetrahedral structure. The compound 1 crystallizes in monoclinic, space group C2/c with a = 20.3151(19), b = 8.7299(9), c = 24.626(2) angstroms, beta = 107.474(2) degrees , V = 4165.9(7) A3. At room temperature, the complex 1 exhibits an intense blue emission at 474 nm upon 380 nm excitation.     

Synthesis, crystal structure and spectroscopic properties of an unsymmetrical compound with carbazole and benzothiadiazole units

An unsymmetrical organic compound with carbazole (Cz) as donor and benzothiadiazole (BTD) as acceptor (D-π-A-π∗-D∗) was designed and synthesized via simple Heck reaction. The unique crystal structure of Cz-BTD-Cz∗ shows a ladder-like packing mode. A two molecule pair stacks parallelly with each other in each packing unit. In each cell, one Cz moiety is connected with BTD by vinylene bond in same plane. However, the other Cz group is connected to BTD by a one-end vinyl bond in almost perpendicular position to the coplanar part of the molecule. The shortest intermolecular plane distance is 3.48 ± 0.1 Å. The photophysical properties of Cz-BTD-Cz∗ in solution and in bulky crystalline powder state were studied. In bulk crystalline powder state, it has a red-shifted emission band peaked at 609 nm relative to that in solution, and the FWHM was reduced to only 58 nm. Electrochemical properties were also investigated.     

A novel series of rhenium-bipyrimidine complexes: synthesis, crystal structure and electrochemical properties

Four novel rhenium complexes of formula [ReCl(4)(bpym)] (1), [ReBr(4)(bpym)] (2) PPh(4)[ReCl(4)(bpym)] (3) and NBu(4)[ReBr(4)(bpym)] (4) (bpym = 2,2'-bipyrimidine, PPh(4) = tetraphenylphosphonium cation and NBu(4) = tetrabutylammonium cation), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of [ReX(4)(bpym)] molecules held together by van der Waals forces. In both complexes the Re(iv) central atom is surrounded by four halide anions and two nitrogen atoms of a bpym bidentate ligand in a distorted octahedral environment. The structures of 3 and 4 consist of [ReX(4)(bpym)](-) anions and PPh(4)(+) () or NBu(4)(+) (4) cations. The coordination sphere of the Re(iii) metal ion is the same as in 1 and 2, respectively. However, whereas the Re-X bonds are longer the Re-N bonds are shorter than in 1 and 2. This fact reveals that the bpym ligand forms a stronger bond with Re(iii) than with Re(iv) resulting in a stabilisation of the lower oxidation state. [ReX(4)(bpym)] complexes are easily reduced, chemically and electrochemically, to the corresponding [ReX(4)(bpym)](-) anions. A voltammetric study shows that the electron transference is a reversible process characterized by formal redox potentials of +0.19 V (1) and +0.32 V (2) vs. NHE, in acetonitrile as solvent.     

Versatile coordinative abilities of a new hybrid pteridine-thiosemicarbazone ligand: crystal structure, spectroscopic characterization, and luminescent properties

The synthesis and characterization of the first thiosemicarbazone-lumazine (TSCLMH=the thiosemicarbazone of 6-acetyl-1,3,7-trimethyllumazine) hybrid ligand is reported. The influence of the conformation of this compound on its energy and the atomic contribution to the molecular orbitals have been theoretically investigated. Ni(II), Cu(I), Zn(II), and Cd(II) complexes of this ligand have been synthesized and characterized by elemental analysis, thermogravimetric studies, IR, 1H, 13C, and 15N NMR, and UV-vis-NIR spectroscopy, magnetic measurements, and X-ray crystallography. Four types of coordination modes for the ligand may be predicted: (a) double bidentate; (b) tetradentate; (c) tridentate; (d) bidentate. Structures of representative complexes of types a, b, and d have been determined by X-ray crystallography. In the [Cu(TSCLMH)]2(ClO4)2 complex, TSCLMH acts as a doubly bidentate bridging ligand forming a dimer with a Cu...Cu distance of 2.876 A. The geometry around the metal ion is trigonally distorted tetrahedral with a relatively long (four-atom) bridge between the metal centers instead of the shorter, mainly single atom, bridges present in other thiosemicarbazone derivatives complexes. In the [Cd(NO3)2(TSCLMH)(EtOH)] complex, the metal ion displays eight-coordinated geometry with the TSCLMH ligand acting in a tetradentate planar fashion and two nitrate anions, one monodentate and the other bidentate. The coordination polyhedron in [Cd(TSCLM)2(H2O)].MeOH.2H2O is a square pyramid with two monoanionic ligands acting as bidentate NS donors and a water molecule completing the coordination sphere. Fluorescence spectroscopic properties of TSCLMH have been studied as well as the changes in position and intensity of fluorescence bands caused by the complexation with different metal ions (Ni2+, Cu+, Zn2+, Cd2+).     

Synthesis, crystal structure and spectroscopic properties of two new complexes containing azido or dicyanamido bridges

Two new complexes, [Cu(L₁){N(CN)₂}]·ClO₄ (1) (L₁ is 1,8-dimethyl-1,3,6,8,10,13-hexa-azacyclotetradecane) and [Co(L₂)(N₃)₂]·ClO₄ (2) (L₂ is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane) have been synthesized and characterized. The compounds crystallize in the monoclinic system P2₁ space group for 1 and P2₁/n for 2. Single crystal X-ray analysis reveals that the compound 1 assumes a one-dimensional structure via hydrogen-bonding interactions, in which each Cu(II) ion is coordinated by four nitrogen atoms from ligand L₁ and one nitrogen atom from [N(CN)₂]⁻ anion. For compound 2, each Co(III) ion is coordinated by four nitrogen atoms of ligand L₂ and two nitrogen atoms from N₃ ⁻ anion.     

Synthesis,crystal structures,spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H₂L¹), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H₂L²); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H₂L³), namely [Co^III(L¹)(N-MeIm)₃]PF₆ (1), [Co^III(L¹)(py)₃]ClO₄ (2), [Co(L¹)(py)₃][Co(L¹)₂] (3) and [Co^III(L²)(N-MeIm)₃]PF₆ (4) and [Co(L³)(N-MeIm)₂]PF₆ (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.     

Formate ion: structure and spectroscopic properties

The formate anion HCOO(-) is present in a multitude of systems of relevance, and it is characterized by its plasticity, adopting several different structures. This work provides a theoretical study of the ion focused on two of these structures, a crystal and an isolated species. Crystals of sodium formate and ammonium formate are studied using CASTEP, a solid-oriented computing package. Individual molecules of the same systems and of the formate and ammonium ions are also studied, using the Gaussian code at the MP2/aug-cc-pvTZ level. All theoretical calculations are contrasted by comparison to observed infrared spectra, recorded by using different techniques. In addition, a topological analysis of the bonding properties of the isolated molecules is presented.     

Synthesis,crystal structure,spectroscopic properties and DFT calculations of a new Schiff base-type Zinc(II) complex

Research on Chemical Intermediates - A new mononuclear Zn(II) complex, [Zn(L 2 )2]·CH3OH (HL 2 &nbsp;=&nbsp;1-(2-{[(E)-3,5-dichloro-2-hydroxybenzylidene]amino}phenyl)ethanone oxime),...     

Nd:GdVO4晶体的生长与光谱性能

采用Czochralski法生长了均匀透明的Nd:GdVO4晶体,测量了其室温偏振吸收谱,并与0.2mol·L^-1的NdCl3溶液的室温吸收谱进行了比较。根据Judd-Ofelt理论,拟合出晶体场唯象强度参数：Ω2=12.629×10^-20cm^2,Ω4=4.828×10^-20cm^2,Ω6=8.425×10^-20cm^2.计算了各能级的辐射跃迁几率AJ,J',振子强度PJ,J;,辐射寿命τ,荧光分支比βJ'等光学参量。并用LD激光器泵浦Nd:GVO4晶体,当量大泵浦功率为26W时,得到输出功率为14.3W波长为1.06μm的基频光,光-光转换效率为55%,斜效率为63%。     

Accidental formation of Gd4(SiO4)2OTe: crystal structure and spectroscopic properties

Designing new functional materials with increasingly complex compositions is of current interest in science and technology. Complex rare‐earth‐based chalcogenides have specific thermal, electrical, magnetic and optical properties. Tetragadolinium bis[tetraoxidosilicate(IV)] oxide telluride, Gd₄(SiO₄)₂OTe, was obtained accidentally while studying the Gd₂Te₃–Cu₂Te system. The crystal structure was determined by means of single‐crystal X‐ray diffraction. The compound crystallizes in the space group Pnma. Three symmetry‐independent gadolinium sites were determined. The excitation and emission spectra were collected at room temperature and at 10 K. Gd₄(SiO₄)₂OTe appears to be a promising optical material when doped with rare‐earth ions.     

New trinuclear carbonato-bridged copper(II) complexes: Synthesis,crystal structure,and spectroscopic properties

New trinuclear carbonato-bridged copper(II) complexes, [Cu₃(Bipy)₆(μ₃-CO₃)](CF₃SO₃)₄(H₂O)_0.5 (I) and [Cu₃(Phen)₆(μ₃-CO₃)](CF₃SO₃)₄(H₂O)_0.5 (II) (Bipy = 2,2′-bipyridine and Phen = 1,10-phenanthroline), have been synthesized and characterized by X-ray crystallography. In the trinuclear units, a carbonate anion triply bridges three Cu atoms in a μ₃-η¹:η¹:η¹-CO₃ mode. The environment around each copper(II) center is five-coordinate ranging between intermediate to distorted square-pyramidal geometry. In the crystal packing, the molecule of I is involved in a variety of intra/intermolecular non-covalent interactions such as intra/intermolecular stacking and CH···π interactions between the pyridine groups of the chelated ligand, leading to a one-dimensional arrangement of I. In complex II, the molecule is involved in both intra- and intermolecular Phen-Phen π-stacking, forming a three-dimensional network. The spectroscopic (IR, diffuse reflectance, and EPR spectra) properties and the preliminary results of magnetic measurements of both complexes are investigated and compared to other closely related trinuclear copper(II) complexes.     

Electronic structure and spectroscopic properties of the two structural isomers of donor-acceptor substituted sesquifulvalene in the gas and solution phases-a case study of sudden polarization

The ground state equilibrium structure and electric properties of two structural isomers of donor-acceptor substituted sesquifulvalene have been calculated at ab initio HF and MP2 levels for different conformations. The electronic properties of low lying excited singlets are calculated by using CI calculations including single excitations only. Isomer I in which the inter-ring charge transfer (CT) is reinforced in the presence of substituents shows sudden polarization in the ground and two lower lying excited states, while isomer II in which the longitudinal CT interaction is attenuated does not exhibit sudden polarization. The phenomenon of sudden polarization has been rationalized in terms of the easy polarization, smaller rotational barrier, and enhanced inter-ring CT on going from the planar to the orthogonal geometry. The appreciably large static second-order polarizability of I stems from its sudden polarized ground state. The solvent (using the conductor-like polarizable continuum model (CPCM)) plays a significant role on the modulation of ground and excited state electronic properties which, in general, predicts blue-shifts for I. However, for molecule II, the two lower energy transitions show a red-shift while the others show a weaker blue-shift at any conformation.     

Self-assembly of a novel series of hetero-duplexes driven by donor-acceptor interaction

The self-assembly of a novel series of donor-acceptor interaction-driven artificial hetero-duplexes in organic media has been described. Four linear compounds 1a-1d, bearing two to five electron rich 1,5-dioxynaphthalene units connected by the tetra(ethylene glycol) linker, respectively, have been prepared and used as donors, while eight compounds 2a-2d, 13-16, bearing one to four electron deficient pyromellitic diimide, 1,4,5,8-naphthalene-tetracarboxydiimide, or perylene-3,4,9,10-tetracarboxydiimide units, respectively, have been used as acceptors. The structure of the hetero-duplexes has been characterized by the ¹H NMR, UV-vis spectroscopy and vapor pressure osmometry. It is revealed that the binding stability of the duplexes vary greatly, depending on the length and structure of the monomers and also the solvent, and hetero-duplex 1d·2d displays a maximum association constant of ca. 1.0×10⁴ M⁻¹ in chloroform.     

Influence of chloromethyl substituent on structure and donor-acceptor properties of 10-methyl-10-chloromethylphenothiasiline

Summary From an x-ray structure study of crystals of 10-methyl-10-chloromethylphenothiasiline, it has been found that the presence of the electron-acceptor substituent CH₂Cl on the Si atom leads to destabilization of the heterocycle, an increase in nonplanarity of the molecule, and a weakening of its aromatic properties, both in the ground state and in the state with charge transfer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2436–2441, November, 1981.The authors wish to thank V. F. Traven' for furnishing the crystals, and A. G. Kozlovskaya for participating in the work.