Synthesis of macrocycles containing 1,3,4-oxadiazole and pyridine moieties

A series of peptide-like 25–28 membered macrocycles containing 1,3,4-oxadiazoles and pyridines bearing a chiral center scaffold have been synthesized by using known coupling reagents and common protecting groups. The yield of the purified macrocycles was poor on an average, yet it seems to be independent of amino acid substitution or stereochemistry. These macrocycles represent a new class of structures for further development and for future application in high-throughput screening against a variety of biological targets.     

Macromolecularization of fullerenes and the charge transfer complex formation of fullerenes with polymers having electron-donating or electron-accepting moieties

C₆₀ was bonded to allylamine homopolymer (PALA) and its copolymers with styrene, 2-hydroxypropyl methacrylate etc. as a pendant functional group. The polyallylamine bonded C₆₀ displays fluorescence at room temperature although C₆₀ does not in itself. This may be due to the lessening of highly symmetrical shape of C₆₀. Some C₆₀-amine adducts are prepared as the model of polyallylamine-C₆₀ for the clarification. C₆₀ doped poly(tetrahydrofurfuryl methacrylate) film has been prepared and its optical non-linearity has been investigated. The charge transfer complexes formation of C₆₀ with polymers having electron-donating chromophore moieties such as poly(dimethylaminostyrene), poly(acryloylphenothiazine), poly(acryloylphenoxazine) and poly(styrene-co-dimethylaminophenylmaleimide) as well as with polymer having electron-accepting chromophore moiety poly(cyanophenylacrylamide) have been manifested.     

The effect of counterion in polymer sulfonates on the synthesis and properties of poly-3,4-ethylenedioxythiophene

The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of the salt and acid forms of polymer sulfonates with different polymer-chain flexibility is studied. The dependence of the rate of synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on the nature of polysulfonate counterion that determines the type and distribution density of the charge in the polyelectrolyte chain is demonstrated. For the Н⁺ form of a rigid-chain polysulfonate, it is found that the specific interactions between parts of its macromolecules lead to destabilization of EDOT?⁺ radical cations, hinder the growth of PEDOT chains, and favor the formation of structures with the high degree of charge localization.     

二联吡啶及其二氮取代衍生物电子性质和非线性光学性质的理论研究

采用量子化学PM3方法优化得到二联吡啶及四种二氮取代衍生物的稳定结构,利用ZINDO-SOS∥PM3方法对它们的二阶和三阶非线性光学性质进行计算.结果表明,该类化合物具有良好的非线性光学性质,其中1,6,1′,6′-四氮取代联苯的β值最大,为73 2082C·m,而2,4,2′,4′-四氮取代联苯的三阶非线性光学性质最显著.     

Investigation of the role of 1,3,4-oxadiazole on the spectroscopic, optical, and electrochemical properties of benzimidazolophanes

The synthesis of 1,3,4-oxadiazole (OXD)-based dicationic cyclophanes has been achieved via an N-alkylation route, and UV-vis spectra proved the absence of charge transfer interactions. Electrochemical studies showed interference of the OXD unit on the characteristic redox properties of dicationic benzimidazolophanes.     

Theoretical studies on the electronic and optical properties of two new alternating fluorene/carbazole copolymers

Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)-co-alt-2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m = 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (Delta(H-L)), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (E(g)s) and the maximal absorption wavelength lambda(abs) of PFmCz (m = 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as Delta(H-L), E(g), IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz)(n) series.     

N－甲基-吡咯烷并[3,4]C60衍生物的结构、电子光谱 和二阶非线性光学性质的 理论研究

利用半经验AM1量子化学方法研究了N－甲基－吡咯烷并[3,4]C60(MPC)及其噻吩取代衍生物(TMPC)的几何结构。电子结构研究表明,MPC及TMPC衍生物的前沿轨道主要由C60部分决定,C60母体与成基团之间存在较强的分子内电荷转移,C60部分是电子受体,而噻吩环部分和吡咯环部分为电子给体。在AM1优化几何构型的基础上,用INDO/SCI方法计算了MPC及TMPC的电子光谱,用完全态求和(SOS)公式计算了其二阶非线性光学性质。结果表明,MPC与TMPC在400nm以上均存在吸收峰,TMPC的这些吸收峰(400nm以上)比MPC的吸收峰强得多,与实验所得结果一致。对于TMPC来说,其二阶非线性光学系数β0值随分子构型不同而有较大的变化,β0值最大可达60×10^-30esu。     

硫化反式聚异戊二烯电子性质的理论化学研究

应用量子化学计算方法,对反式聚异戊二烯本征态和硫化态结构的能量及电子性质等进行了计算.结果表明,当聚异戊二烯掺杂硫后,相邻两链之间的距离a⊥变窄,体系的总能量降低,从而使整个掺杂体系更加稳定.另外,在硫化聚异戊二烯分子中,S原子位于两个相邻聚异戊二烯链之间,并偏向于其中一个分子链的C C双键的一侧,即与相邻两链中相对应的两个C C双键形成π-p-π共轭体系,增加了电子在两个聚异戊二烯链间的流动性,从而使硫化的反式聚异戊二烯更加稳定.另外,根据固体能带理论,采用量子化学EHMO方法,对反式聚异戊二烯本征态和硫掺杂态的能带结构进行了计算,根据硫化前后能隙和带宽的变化,解释了反式聚异戊二烯掺杂后呈现电导率各向异性的原因.     

荧光素及其衍生物电子结构与光谱性质的理论研究

用ZINDO、从头算和密度泛函理论方法研究荧光素及其衍生物的电子结构和光谱性质.计算结果表明母体双阴离子荧光素分子(1)与单(2)、双(3)取代形成的单阴离子荧光素分子的基态电子结构不同,而且1与2和3的基态和激发态的电子转移方向相反.体系1~3的最大吸收波长依次发生红移,与实验结果相符合.     

Theoretical and experimental studies of electronic effects and second-order nonlinear optical properties of some benzenecarbothioates and benzenecarbodithioates

The relative nonlinear efficiency of some conjugated ester, thioester and dithioester molecules was investigated by quantum chemical semi-empirical methods. The results of calculations on ground and excited states properties and on finite-field hyperpolarizabilities allowed to select the best compounds for quadratic nonlinear optics. Some of these molecules were synthesized and the theoretical results were confronted with the experimental NLO response obtained by EFISH measurements. It was concluded from this analysis that the dithioester substituent represents an interesting electron-accepting group for applications in nonlinear optics and can be used instead of the nitro group. Correspondence to: A. Botrel     

Optical and electronic properties of siloxane-bridged cyclic dimers with naphthylene or pyrenylene moieties

The optical and electronic properties of novel siloxane-bridged cyclic dimers with naphthylene (CD1) or pyrenylene (CD2) moieties are described. CD1 and CD2 were obtained by the cyclic dimerization of 1,4-bis(dimethylhydroxysilyl)naphthalene (M1) and 1,6-bis(dimethylhydroxysilyl)pyrene (M2), respectively. CD1 and CD2 mainly exhibited the emission from their excimers owing to their short distances between aryl moieties in CD1 and CD2, which were determined to be 3.44 Å and 3.41 Å by the X-ray crystallographic analysis, respectively. The absorption spectra of CD2 in the presence of 7,7,8,8-tetracyanoquinodimethane (TCNQ) revealed that CD2 has the ability to form 1:1 charge-transfer complex with TCNQ, indicating the existence of the transannular π-π interaction between closely located pyrene components in CD2.     

Theoretical studies of structural and electronic properties of AlnAsn clusters

We present theoretical results of size dependent structural, electronic, and optical properties of ligand‐free stoichiometric Al_nAs_n clusters of zinc‐blende modification. The investigation is done using a simplified parametrized linear combination of atomic orbital–density functional theory‐local density approximation–tight‐binding (LCAO–DFT–LDA–TB) method and consider clusters with n up to around 100. Initial structures have assumed as spherical parts of infinite zinc‐blende structure and then allowed to relax to the closest local‐energy‐minimum structure. We analyze the radial distributions of atoms, Mulliken populations, electronic energy levels (in particular, HOMO and LUMO), bandgap, and stability as a function of size and composition. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Synthesis,characterization and comparative study of mesomorphic properties of some new compounds containing both 1,2,4- and 1,3,4-oxadiazole moieties linked in the same molecule

One new homologous series of compounds containing 1,2,4- and 1,3,4-oxadiazole rings in the same molecule was synthesized. 3-(4-Butoxyphenyl)-5-{4-[5-(4-alkoxyphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-1,2,4-oxadiazole (VII)_1–8 were synthesized by several procedures. This series has been characterized by FT-IR and ¹H NMR spectroscopy. Their liquid crystalline properties were studied by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). This series did not show any liquid crystalline behaviors and only crystal to isotropic liquid transition was observed.     

Modification of the electrochemical and electronic properties of electrogenerated poly(3,4-ethylenedioxythiophene) by hydroxymethyl and oligo(oxyethylene) substituents

Ethylenedioxythiophene (EDOT) derivatives with hydroxymethyl and oligo(oxyethylene) groups covalently attached at the ethylenedioxy bridge have been synthesized. The hydroxymethyl group considerably increases the ability of EDOT to electropolymerize in water and the electroactivity of the polymer in aqueous media. The electrochemical and optical properties of the oligo(oxyethylene)-substituted polymer reveal a negative shift of the oxidation potential and a significant enhancement of the effective conjugation length with a 0.10 eV decrease of the bandgap. The optical spectra of the polymer undoped in the presence and absence of oxygen indicate a high sensitivity of the polymer towards molecular oxygen, suggesting possible spontaneous doping by molecular oxygen.     

Design of organic semiconductors: tuning the electronic properties of pi-conjugated oligothiophenes with the 3,4-ethylenedioxythiophene (EDOT) building block

Hybrid oligothiophenes based on a various combinations of thiophene and 3,4-ethylenedioxythiophene (EDOT) groups have been synthesized. UV/Vis absorption spectra show that the number and relative positions of the EDOT groups considerably affect the width of the HOMO-LUMO gap and the rigidity of the conjugated system. Analysis of the crystallographic structure of two hybrid quaterthiophenes confirms that insertion of two adjacent EDOT units in the middle of the molecule leads to a self-rigidification of the conjugated systems by intramolecular SO interactions. Cyclic voltammetry data shows that the first oxidation potential of the oligomers decreases with increasing chain length and increasing number of EDOT groups for a given chain length. Electrochemical studies and theoretical calculations show that the positions of the EDOT units in the conjugated chain control the potential difference (DeltaE(p)) between the first and second oxidation steps. Moving the EDOT groups from the outer to the inner positions of the conjugated system increases DeltaE(p). Theoretical calculations confirm that this phenomenon reflects an increase of the intramolecular coulombic repulsion between positive charges in the dication. A thin-film field-effect transistor was fabricated by vacuum sublimation of a pentamer with alternating thiophene-EDOT structure, and the hole mobility was determined.     

洛汾碱衍生物的电子结构及光谱性质的理论研究

采用密度泛函理论(DFT)的B3LYP/6-31G*方法,对4种洛汾碱类化合物的几何构型进行了优化,在此基础上计算分子的电子结构,并结合有限场FF方法研究了二阶非线性光学(NLO)性质.用含时密度泛函理论(TD-DFT)对上述化合物分子进行吸收光谱的研究.研究表明在4,5-二-苯基-2-对甲酰苯基咪唑生色团中4,5苯环上引入硝基和3位N原子引入苄基改变分子的共轭平面,使二阶非线性极化率总有效值(βtot)减小,吸收峰总体蓝移.同时还发现,在CH2Cl2溶剂中a和c分子的λmax主要来源于HOMO→LUMO的π一π*跃迁,b和d分子的λmax主要来源于HOMO→LUMO+2的π→π*跃迁.     

Theoretical studies on the structure and electronic properties of aryl sulfides and sulfones

Molecular orbital calculations are reported on the structure and electronic properties of diphenyl sulfide using both semiempirical and ab initio methods. Neither the MNDO nor AM1 methods give satisfactory structures, but better results are obtained with the PM3 method. At the ab initio level, the 4-31G basis set with polarization functions on sulfur alone (4-31G/S*) gives comparable results to those obtained with the 6-31G** basis set. The corresponding bond lengths and angles at the sulfur atom of 4-aminophenyl-4′-nitrophenyl sulfide and related derivatives of diphenyl sulfone, diphenyl disulfide, and phenylthiosulfonate calculated at the 4-31 G/S* level show a good correlation with crystallographic data where available. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 141–147, 1998     

Theoretical investigations of the elastic,electronic, optical and thermodynamics properties of SrSi

The crystal structural, electronic, optical and thermodynamic properties of SrSi are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). We have calculated the ground states properties and they are in good agreement with the available experimental data and other theoretical results. We have obtained the electronic structure and density of states, and the results showed that both of Immm and Cmcm phases are metal material. The elastic properties such as elastic constants, shear modulus, Young's modulus and Poisson's ratio are obtained for the first time. Furthermore, the optical properties are reported for radiation up to 30 eV. Finally, the thermodynamic properties of Cmcm phase such as free energy, entropy, enthalpy, heat capacity and Debye temperature are given for reference.     

两种C~6~0双炔衍生物的结构、光谱和二阶非线性光学性质的 理论研究

用INDO/2和INDO/SCI方法,计算了C~6~0C(C=CH)~2基态电子结构和电子光谱,所得结果与实验结果基本一致.在此基础上,设计了C60(C=CH)~2,并用同样方法计算了电子结构和光谱.在正确的电子光谱基础上,用ZINDO-SOS方法计算了2个分子的二阶非线性光学系数β~i~j~k和β~μ,并对其结果进行了分析和讨论.结论是,乙炔基与C~6~0(C=CH)~2有更大的非线性光学系数,是有希望的非线性光学备选材料分子。     

Modulation of the electronic properties of conjugated polymers through design of polymer backbone

We present the results of valence effective hamiltonian (VEH) band structure calculations on stereoregular block copolymers of poly(thienylene vinylene) and poly(pyrrylene vinylene). We have examined the evolution of the electronic properties as a function of the extension and distribution of the block copolymer sequences. In both cases, the electronic-properties deviate from a linear evolution as a consequence of the localization of both HOCO and LUCO.