Semi-metallic single-component crystal of soluble La@C82 derivative with high electron mobility

We prepared an organic conductor crystal having extremely high electron mobility, in which the adamantylidene (Ad) derivative of La@C(82) (an endohedral metallofullerene known as a n-type semiconductor) is aligned in an orderly fashion. The single-component crystal exhibits high electron mobility of μ > 10 cm(2) V(-1) s(-1) along the c axis under normal temperatures and pressures in the atmosphere, as shown by flash-photolysis time-resolved microwave conductivity (TRMC) measurements, which are the highest of reported organic conductors measured by TRMC. According to density functional calculations, the single crystal of La@C(82)Ad is semi-metallic, with a small band gap of 0.005 eV.     

Three-chain truxene discotic liquid crystal showing high charged carrier mobility

A new truxene discotic liquid crystal possessing only three octyloxy chains (3C8OTRX) was studied on the mesomorphic and semiconducting properties to reveal that it exhibits a high drift mobility of positive carriers in the order of 10(-2) cm(2) V(-1) s(-1) in the hexagonal ordered columnar (Col(ho)) mesophase.     

Aceno[2,1,3]thiadiazoles for field-effect transistors: synthesis and crystal packing

An efficient synthetic approach to a series of aceno[2,1,3]thiadiazole derivatives is described. 2-TIPS and 2-TES molecules exhibited different crystal packings, and 2-TIPS show good device performances with hole mobility up to 0.4 cm(2) V(-1) s(-1) and an average mobility of 0.15 cm(2) V(-1) s(-1) as the active material for organic field-effect transistors. All of the results demonstrate these aceno[2,1,3]thiadiazole derivatives as promising materials for optoelectronic devices.     

An asymmetric oligomer based on thienoacene for solution processed crystal organic thin-film transistors

A novel thienoacene-based conjugated oligomer, i.e.BTTT-T-C12, was designed and synthesized. Its highly asymmetric structural feature enables the preparation of two-dimensional single-crystalline thin films in millimetre size and ~100 nm thick by a solution processing method directly on the Si/SiO(2) substrate. Single crystal organic thin film transistors exhibit a mobility of 0.70 cm(2) V(-1) s(-1) and an on/off ratio of 5.7 × 10(4).     

Optical and morphological characterization of polyacrylamide hydrogel and liquid crystal systems

In this work, the thermotropic liquid crystal MBBA (N-(4-methoxybenzilidene)-4-butylaniline), entrapped on hydrogels, based on cross-linked polyacrylamide (PAAm), was studied. The liquid crystalline phases of system were characterized by polarized optical microscopy (POM), refractive index, optical transmittance, scanning electron microscopy (SEM) and water loss. It was verified the presence of birefringence on hydrogel + liquid crystal. The dynamic of formation of such birefringence finished 40 days after the hydrogel synthesis. The effective birefringence Δn, i.e., the difference on refractive index of polyacrylamide hydrogel to refractive index of hydrogel + liquid crystal (Δn₁) and the difference on refractive index of liquid crystal (MBBA) to refractive index of hydrogel + liquid crystal (Δn₂) are dependent of content of acrylamide (AAm) and MBBA on hydrogel. The increase on Δn₁ and Δn₂ with the polyacrylamide content on hydrogel was attributed to decreasing of the mobility liquid crystal inside the hydrogel. Also, an increase on MBBA concentration in the polymeric matrix provides a reduction in the values of optical transmittance in the system. The morphology observed by SEM shows that hydrogel + liquid crystal is more compact that PAAm hydrogels. The presence of MBBA causes an increase in hydrophobicity. The water loss speed is favored by the increase in the amount of MBBA present in the hydrogels.     

High performance n-type single crystalline transistors of naphthalene bis(dicarboximide) and their anisotropic transport in crystals

High-performance n-type organic single crystal transistors of a naphthalene diimide are demonstrated. The accomplished transistors exhibit electron mobility as high as 0.7 cm(2) V(-1) s(-1). The anisotropic charge transport in the elongated hexagonal crystals of the naphthalene diimide is also explored. The transport anisotropy along different directions is at least 1.6 (mobility ratio).     

Reinvestigation of carrier transport properties in liquid crystalline 2-phenylbenzothiazole derivatives

We have reinvestigated the charge carrier transport properties in a liquid crystal of 2-(4'-heptyloxyphenyl)-6-dodecylthiobenzothiazole (7O-PBT-S12), for which the electronic conduction was first established in rodlike liquid crystals and for which the highest hole mobility in the smectic A (SmA) phase ever achieved was reported. We found that 7O-PBT-S12 exhibited three crystal phases, one of which appeared in a limited temperature range of 10 degrees just below the phase transition temperature from the SmA phase. In this crystal phase, nondispersive transient photohole currents were observed in time-of-flight experiments, and its hole mobility was determined to be 8 x 10(-3) cm(2)/Vs, slightly higher than that reported previously in the SmA phase. For the SmA phase, however, the hole mobility was 1 x 10(-4) cm(2)/Vs. Furthermore, we established the electron transport in the SmA phase of purified 7O-PBT-S12, whose mobility was the same as the hole mobility in that phase. In order to confirm generality of the new findings in 7O-PBT-S12, we investigated the carrier transport properties of its derivative having a short hydrocarbon chain, 2-(4'-heptyloxyphenyl)-6-butylthiobenzothiazole (7O-PBT-S4), and obtained comparable results. The present results correct a mistake in the previous report and give an idea of what a typical mobility in the SmA phase is. On the basis of these results, we discuss what determines the charge carrier mobility in smectic mesophases.     

n-channel polymers by design: optimizing the interplay of solubilizing substituents, crystal packing, and field-effect transistor characteristics in polymeric bithiophene-imide semiconductors

Electron transporting (n-channel) polymer semiconductors for field-effect transistors are rare. In this investigation, the synthesis and characterization of new electron-depleted N-alkyl-2,2'-bithiophene-3,3'-dicarboximide-based pi-conjugated homopolymers and copolymers containing the 2,2'-bithiophene unit are reported. A novel design approach is employed using computational modeling to identify favorable monomer properties such as core planarity, solubilizing substituent tailorability, and appropriate electron affinity with gratifying results. Monomeric model compounds are synthesized to confirm these properties, and a crystal structure reveals a short 3.43 A pi-pi stacking distance with favorable solubilizing substituent orientations. A family of 10 homopolymers and bithiophene copolymers is then synthesized via Yamamoto and Stille polymerizations, respectively. Two of these polymers are processable in common organic solvents: the homopolymer poly(N-(2-octyldodecyl)-2,2'-bithiophene-3,3'-dicarboximide) (P1) exhibits n-channel FET activity, and the copolymer poly(N-(2-octyldodecyl)-2,2':5',2':5',2'-quaterthiophene-3,3'-dicarboximide) (P2) exhibits air-stable p-channel FET operation. After annealing, P1 films exhibit a very high degree of crystallinity and an electron mobility > 0.01 cm (2) V(-1) s(-1) with a current on-off ratio of 10 (7), which is remarkably independent of film-deposition conditions. Extraordinarily, P1 films also exhibit terracing in AFM images with a step height matching the X-ray diffraction d spacing, a rare phenomenon for polymeric organic semiconductors. Another fascinating property of these materials is the air-stable p-channel FET performance of annealed P2 films, which exhibit a hole mobility of approximately 0.01 cm(2) V(-1) s(-1) and a current on-off ratio of 10(7).     

两种四噻吩并萘分子晶体电荷传输性质的理论研究

采用密度泛函理论(DFT)方法结合不相干的电荷跳跃模型和随机Monte Carlo模拟,研究了2种四噻吩并萘晶体(AT1和AT2)的分子结构、电子性质及电荷载流子传输参数,并预测了这2种晶体室温下空穴和电子迁移率的各向异性.结果表明标题化合物具有近似平面的刚性骨架结构,电荷传输过程中分子的结构弛豫相当小.基于绝热势能面法计算的AT1和AT2分子空穴/电子传输内重组能分别为9.300×10~(-2)/1.100×10~(-1)eV和1.020×10~(-1)/1.290×10~(-1) eV,外重组能分别为1.835×10~(-2)/1.711×10~(-2) eV和1.857×10~(-2)/1.747×10~(-2) eV.利用Monte Carlo随机模拟方法预测的2种分子晶体室温(300K)下空穴/电子迁移率平均值分别为4.976×10~(-3)/2.766×10~(-2) cm~2 V~(-1)s~(-1)和3.857×10~(-3)/1.478×10~(-2)cm~2 V~(-1)s~(-1).此外,迁移率的角度依赖性研究表明2种载流子在AT1和AT2晶体aob平面传输时表现出显著的各向异性,其最大值均沿着电荷传输积分最大的方向,为制备高性能场效应晶体管器件提供了参考.     

烯氨酮晶体结构研究

研究了氨基分别为1'-四氢吡咯,1'-六氢吡啶和4'-吗啉的1-苯基-3-氨基-2-丁烯-1-酮的晶体结构. 它们的构型.构象均为trans, S-cis.由于共轭体系的扩展,这些烯氨酮的氮原子都比相应的烯胺有程度更大的电子离域,其中又以扭式构象的四氢吡咯基的离域程度最高.四氢吡咯形成N-不饱和化合物的特殊活性与此有关.     

沙蚕磷草酸盐的合成与晶体结构

合成了一种新的有机磷杀虫剂沙蚕磷[O,O,O',O'-四甲基－S,S'-(2-N,N-二甲氨基-1,3-亚丙基)-双-二硫代磷酸酯],并制备了它的草酸盐。测定了沙蚕磷草酸盐的晶体结构,结果表明,该晶体属三斜晶系,P1空间群,晶胞参数为:a=0.74342(5)nm,b=1.1057(4)nm,c=1.45295(11)nm,α=98.018(11)°,β=101.012(4)°,γ=96.224(10)°,Z=2。通过元素分析,MS、IR及^1H,^1^3CNMR表征了该化合物的结构。     

FT-IR study of liquid crystal molecules on alignment layers

Alignment control at the molecular level is crucial for realizing high-performance LCDs. In particular, the structure of the interface between the liquid crystal and the alignment layer must be clarified. By utilizing RAS (reflection-absorption spectroscopy), a highly sensitive FT-IR spectroscopic technique, we have obtained the following information about the orientation of liquid crystal molecules; (1) the cyano group in a liquid crystal molecule behaves like an electron donor with respect to an SiO layer, but like an electron acceptor with respect to a polyimide layer; (2) with the use of polarized IR spectroscopy, it was discovered that the liquid crystal 8CB is aligned with a slant away from the aligning direction, regardless of the type of alignment layer. The angle between the molecular short axis within the plane of the core and the surface normal was found to be smaller on polyimide layers than on SiO layers.     

Roles of inter- and intramolecular vibrations and band-hopping crossover in the charge transport in naphthalene crystal

We calculate the hole and electron mobilities in naphthalene crystal from 10 to 300 K within the framework of the Holstein-Peierls model coupled with first-principles density-functional-theory-projected tight-binding band structures. All the electron-phonon coupling constants, including both local and nonlocal parts for inter- and intramolecular vibrations, have been taken into considerations through density functional theory. The band-hopping crossover transition temperature for the electron transport in the c' axis is calculated to be around 23 K. We have identified a few high frequency intramolecular vibrations which are very important to the charge transport in naphthalene crystal due to their comparatively large electron-phonon coupling constants. However, their contributions to the temperature dependence of mobility are minor because of the small phonon occupations and small nonlocal coupling strengths. The low frequency intermolecular modes (longitudinal optical modes) are found to be the major contributions to the temperature dependent charge transfer properties in naphthalene crystal. Even though the calculated qualitative temperature dependence is in agreement with experiment, the predicted absolute mobility is about one to two orders of magnitude larger.     

Influence of the alkyl and alkoxy side chains on the electronic structure and charge-transport properties of polythiophene derivatives

Density Functional Theory has been used to study the structural, electronic and charge-transport properties of two regio-regular head-to-tail polythiophene derivatives, i.e. poly(3-hexyl-thiophene), P3HT, and poly(3-oxyhexyl-thiophene), P3OHT. The effect of substituents on the electronic structure was analyzed by means of bandwidth, bandgap, effective mass, total and partial densities of states and crystal orbital overlap populations. Electronic couplings were estimated from band diagrams as the splitting of the valence band. The neutral and cationic states of isolated oligomers were optimized using the supercell approximation. The hole-transfer rates and mobilities were evaluated according to Marcus's theory. Results provide a compelling illustration of the effect of side chains on the crystal packing, electronic structure and charge-transport properties. Thus, the hole mobility calculated for the alkyl derivative was 0.15 cm(2) V(-1) s(-1) (experimental mobility is 0.10 cm(2) V(-1) s(-1)), while the alkoxy derivative has a theoretical mobility of 0.49 cm(2) V(-1) s(-1). The obtained results hopefully could motivate experimentalists to try out P3OHT for an improved charge carrier mobility.     

香草醛晶体光学非线性系数的有限场方法研究

采用有限场方法计算了有机非线性材料3-甲氧基-4-羟基-苯甲醛(分子式C~8H~8O~3,简称MHBA)的二阶非线性光学系数d~2~1,d~2~2,d~2~3,d~2~5。研究结果表明在MP2近似和6-31G+(p,d)基组水平上理论值能较好地与实验值符合,同时也表明拉电子基团HC＝O和推电子基团HO对MHBA分子的光学非线性性能的影响很大,而晶体中分子间的氢键作用对d值的贡献很小。     

Liquid crystal compound anti-ice surface

In some cold areas/regions, ice accumulation is harmful to aircrafts, highways and power lines. To overcome this challenge, many researchers have focused on developing anti-icing surfaces. In this paper, liquid crystal compound Cholest-5-en-3-ol(3β)-4-(2-propenyloxy)benzoate was synthesised, and a liquid crystal surface (LC surface) is prepared by heating the liquid crystal compound to 250°C and then cooling it. We determined ice-phobic properties of LC surface using differential scanning calorimetry (DSC) and polarised optical microscope (POM). A phenomenon that the freezing of water droplet on the LC surface is delayed was found. Compared with the two measurement methods, we obtained similar result that water freezing temperature was delayed nearly by 8°C on average on the LC surface. A process of ice/frost formation is observed using POM. The results displayed that the glass wafer without LC was covered completely by ice/frost, whereas on the LC surface at the same temperature no ice/frost was formed. Characteristics of LC surface were observed by field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) imaging system. We suggest that the reason behind anti-ice surface is related to surface molecules and this is an important factor which may have an effect on anti-icing property.     

Mechanism of linear and nonlinear optical properties of the urea crystal family

First-principles calculations of the second-order optical response functions and the dielectric functions of urea [CO(NH(2))(2)] and some of its derivatives such as monomethylurea (H(2)NCONHCH(3), MMU), and N,N'-dimethylurea (H(3)CHNCONHCH(3), DMU) crystals are performed. On the basis of the density functional theory (DFT) in the local-density approximation (LDA), the highly accurate full-potential projected augmented wave (FP-PAW) method was used to obtain the electronic structure. Over a wide frequency range (0.0-10.0 eV), the dielectric constants and second-harmonic generation (SHG) susceptibilities of the urea crystal family have been obtained, and the results are in good agreement with the experimental values. The origin of the linear and nonlinear optical (NLO) properties of the urea crystal family has been analyzed by coupling the calculated electronic structure and optical spectrum. The prominent spectra of χ((2)) are successfully correlated with the dielectric function ε(ω) in terms of single-photon and double-photon resonances. The virtual electron (VE) and virtual hole (VH) processes have also been performed for the urea crystal family. From the research into the electron deformation density, crystal configuration, substitutional group, and so forth, it is found that the origin of the SHG of the urea crystal family is the charge transfer due to the strong "(?)push-pull" effect along the hydrogen bond, which favors a head-to-tail arrangement of the molecules and enhances the SHG response. The electron-donating substitutional group supplies more electrons to the electron-accepting group, and helps to form large dipoles in molecules. The influence on the NLO properties of the local symmetry of the substitutional group is also discussed in detail.     

Superstructure-dependent optical and electrical properties of an unusual face-to-face, pi-stacked, one-dimensional assembly of dehydrobenzo[12]annulene in the crystalline state

To develop a novel pi-conjugated molecule-based supramolecular assembly, we designed and synthesized trisdehydrotribenzo[12]annulene ([12]DBA) derivative 2 with three carboxyl groups at the periphery. Recrystallization of 2 from DMSO gave a crystal of the solvate 23 DMSO. Crystallographic analysis revealed, to our surprise, that a face-to-face pi-stacked one-dimensional (1D) assembly of 2 was achieved and that the DMSO molecule played a significant role as a "structure-dominant element" in the crystal. This is the first example of [12]DBA to stack completely orthogonal to the columnar axis. To reveal its superstructure-dependent optical and electrical properties, 2 and its parent molecule 1, which crystallizes in a herringbone fashion, were subjected to fluorescence spectroscopic analysis and charge-carrier mobility measurements in crystalline states. The 1D stacked structure of 2 provides a red-shifted, broadened, weakened fluorescence profile (lambda(max) = 545 nm, phi(F) = 0.01), compared to 1 (lambda(max) = 491 nm, phi(F) = 0.12), due to strong interactions between the p orbitals of the stacked molecules. The charge-carrier mobility of the single crystal of 23 DMSO, as well as 1, was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The single crystal of 23 DMSO revealed significantly-anisotropic charge mobility (sigma(mu) = 1.5x10(-1) cm(2) V(-1) s(-1)) along the columnar axis (crystallographic c axis). This value is 12 times larger than that along the orthogonal axis (the a axis).     

Impact of structure and morphology on charge transport in semiconducting oligomeric thin-film devices.

We investigated various thin-film morphologies of vacuum-deposited highly luminescent 2,5-di-n-octyloxy-1,4-bis[4'-(styryl)styryl]benzene (Ooct-OPV5) in a typical light-emitting-diode device structure. Important modifications in the thin-film morphology and structure were obtained by changing the substrate temperature in the range 23-90 degrees C. Structural analysis by X-ray and electron diffraction provided clear evidence for polymorphism in evaporated thin films of Ooct-OPV5. Concomitantly, the hole mobility in the corresponding devices was determined by transient electroluminescence measurements. We demonstrate that the substrate temperature T(sub) is a key parameter that controls the hole mobility of the devices. Increasing T(sub) between 23 and 84 degrees C results in a progressive increase of the zero-field hole mobility from 10(-6) to 10(-4) cm(2) V(-1) s(-1). The increase in hole mobility is correlated to the average grain size in the thin films. In addition, we give evidence for the existence of a peculiar growth mode in the bulk crystal structure of Ooct-OPV5, whereby the (a,b) and (b,c) planes can grow in a homoepitaxial manner.     

Synthesis,crystal structures and electrochemical properties of two new metal-centered ferrocene complexes

Two new metal-centered ferrocene complexes Ni(SCN)2(L)4 (1) and Cu(OAc)2(L)2 (2) (L = 1-[1-ferro- cenylmethyl]imidazole) have been synthesized and characterized by elemental analysis, single crystal X-ray diffraction analysis, spectroscopic and cyclic voltammetric measurements. The geometry of Ni(Ⅱ) in 1 is octahedral, with four ligands in the equatorial plan and two thiocyanate anions at the axial site, while that of Cu(Ⅱ) in 2 is a distorted octahedron formed by two chealted OAc- and two ligands. Single c...