苯丙炔酸和苯丙烯酸酯苯并菲盘状液晶电荷传输的理论研究

电荷传输是有机材料的重要性质之一．根据电子转移的半经典模型对含苯丙炔酸和苯丙烯酸酯支链的苯并菲盘状液晶化合物分子的电荷传输性质进行理论研究．研究结果表明,所计算的三个苯并菲衍生物分子均具有高的电荷传输性能．标题化合物分子的负电荷传输速率均比苯并菲大,含苯丙烯酸酯链的苯并菲分子比含苯丙炔酸酯链的苯并菲分子具有较大的空穴传输速率及较小的负电荷传输速率．对于含苯丙烯酸酯链的苯并菲分子,链烷氧基越长,正电荷传输速率越大,负电荷传输速率越小．     

羟基取代苯并菲化合物分子的结构与电荷传输性质研究

在量子化学B3LYP/6-31G**水平上对苯并菲, 氟及羟基取代苯并菲化合物分子及其分子离子的结构进行理论研究, 得到稳定构型. 在此基础上, 计算二聚物的单点能随旋转角度和盘间距离的变化关系, 得到能量最低点. 根据电子转移的半经典模型计算了苯并菲及氟和羟基取代苯并菲化合物分子的电荷转移常数, 氟和羟基的引入使正电荷转移速率常数明显减小, 即不利于正电荷的传输, 对负电荷的传输速率常数影响不大.     

含酯基和酰胺基支链的苯并菲液晶电荷传输性质的量子化学研究

根据Marcus半经典模型,计算了支链中含酰胺基和含酯基的苯并菲盘状液晶化合物C18H6(OC2H5)3(OCH2CONHCH3)3和C18H6(OC2H5)3(OCH2COOCH3)3的电荷转移反应的速率常数。这两种化合物的支链都可以对称性分布,也可以非对称性分布。计算表明,支链排列的对称性对电荷转移矩阵元和电荷传输速率常数的影响很大,非对称性分子的正电荷传输速率常数和负电荷传输速率常数均大于对称性分子。所以,取代基非对称性排列对增加电荷传输速率常数有利。其原因是支链非对称排列的分子的质量中心与几何中心不重合,当液晶分子绕质量中心旋转的同时形成了分子间的相对平移,从而增大了电荷转移矩阵元。本文为设计、改善液晶分子的电荷传输性能提供了一条新的思路。     

苯并咪唑苯并异喹啉酮及其衍生物的电子结构和光谱性质的理论研究

采用密度泛函、含时密度泛函和单激发组态相互作用(CIS)方法研究了苯并咪唑苯并异喹啉酮(1)及其衍生物的电子结构特性和光谱性质,并用极化连续模型考虑了溶剂的影响.结果表明,化合物1及其衍生物的吸收和荧光发射过程的电子垂直跃迁是由于分子内的电荷迁移.化合物1中取代基的位置及给吸电子能力影响其HOMO-LUMO能隙和电荷迁移量.在分子中引入吸电子和给电子取代基,均使最大吸收波长和最大荧光发射波长红移,计算的结果与实验结果吻合得较好.     

雪花胺类化合物的三维构效关系研究

雪花胺是一类重要的乙酰胆碱脂酶抑制剂，有可能发展成治疗阿尔茨海默病的药物. 利用分子力学计算得到了这类化合物的优势构象，并对这些化合物进行了CoMFA研究．发现，对于雪花胺类化合物，影响其药效的主要因素是空间结构，电荷作用力的影响较小．对空间因素的进一步分析发现，对于该类分子，不宜用空阻较大的基团进行取代．由电荷影响的分析得到了在不同位置上取代基所应有的电荷性质．三维定量构效关系研究为基于雪花胺的抑制剂设计提供了方案．     

分子内氢键 Ⅰ.分子内氢键的PMO研究

脂肪族化合物的分子内氢键与分子间氢键无论在性质和强度上都没有明显的区别,而在共轭体系中的分子内氢键强度却可成倍地大于类似官能团间的分子间氢键,这为应用PMO方法来研究含杂交替烃体系中的分子内氢键提供了可能性.观察到如下规律:对于相同官能团的一系列化合物,分子内氢键的强度主要决定于给予原子上的电荷密度,电荷密度越大,内氢键越强;在非键分子轨道系数相同的情况下,共轭体系越大,内氢键越强.当分子中有脂并环取代基时不服从上述规律.这种脂并环取代基有时会增强内氢键的强度.     

基于星射状三苯胺敏化剂的分子设计

以性能优良的三苯胺星射状分子WD8为母体,通过密度泛函理论方法,探讨了取代基团在不同位置时,对母体分子电子性质、光谱性质和电荷传输性能的影响.结果表明,取代基团位置的不同,对分子的前线分子轨道组成基本没有影响.当2-氰基-3-呋喃基-丙烯酸基团取代位置由对位变为间位时,分子的吸收范围最大.当2-氰基-3-呋喃基-丙烯酸基团和1个吩噻嗪-苯基团取代位置由对位变为间位时,分子的EHOMO最大,ELUMO和Eg最小,分子的最大吸收波长最长.当2-氰基-3-呋喃基-丙烯酸基团和2个吩噻嗪-苯基团取代位置由对位变为间位时,分子的电荷传输性能最强.     

六烷氧基取代的苯并菲和六氮杂苯并菲盘状液晶中的电荷转移

用电子转移的半经典模型在量子化学B3LYP/6-31G(d)水平(对单体)和B3LYP/STO-3G水平(对二聚物)对六烷氧基取代的苯并菲和六烷氧基取代的六氮杂苯并菲组成的盘状晶体系的电荷转移性质进行了研究,发现在用量子化学方法研究电荷转移反应时,不能简单地用氢氧基代替长链烷氧取代基。由于在电荷转移反应中,要考虑参与反应的分子之间前线轨道的细微差别,所以将长链取代基用氢氧基取代,可能得不到定性正确的结果。     

巯基偶氮苯单分子电子传输的取代基效应

用密度泛函理论B3LYP/6-31G**计算巯基偶氮苯分子及分子离子的空间构型和电子结构, 研究取代基对巯基偶氮苯单分子电子传输的影响. 结果表明, 拉电子基(—COOH、—NO2)的引入, 可以提高巯基偶氮苯单分子电子传输体系的稳定性, 使体系LUMO的离域性增高、S原子反应活性增强、HOMO-LUMO能隙显著减小, 进而降低电子传输能垒, 有利于分子电子传输. 相同取代基的分子离子比分子具有更小的HOMO-LUMO能隙, S—Au键更易形成, 金属-分子-金属结构的电子传输性更强.     

分子内氢键——Ⅴ.N-甲基-2-邻羟基芳香基苯并咪唑的合成及分子内氢键

本文报道N-甲基取代邻羟基芳香基苯并咪唑的合成,并研究了此类螯合剂的分子内氢键的性质。在合成N-甲基芳香基苯并咪唑或芳香基苯并咪唑过程中进行的N-甲基化时,随着(?)NH基N上的电荷密度增加和取代基空间位阻的增大,产率急剧下降。羟基的化学位移,离解常数和HMO计算均表明2-(邻羟基芳香基)-苯并咪唑、(口恶)唑、噻唑等化合物均具有较弱的分子内氢键。由于五员共轭环的生成,内氢键强度与结构之间的规律性很差。这与前文~[7]关于邻苯基偶氮芳香酚和2(-邻羟基苯基)喹啉的结果不同。     

Theoretical study on the charge transport properties of triphenylene discogens with a phenylpropionyloxy or 3-phenylpropenoyloxy side chain

Charge transport is one of the most important properties in organic materials. Charge transport properties of triphenylene discogens with a phenylpropionyloxy or 3-phenylpropenoyloxy side chain have been investigated computationally on the basis of semi-classical Marcus theory. The results show that three triphenylene derivatives have high charge mobility. Title compounds have much better electronic mobility than the triphenylene. The triphenylenes containing 3-phenylpropenoyloxy have better hole mobility, but smaller electronic mobility than the triphenylenes with phenylpropionyloxy. For the triphenylene discogens with a phenylpropionyloxy, the longer the alkloxy chains, the better the positive charge transfer rate, but the smaller the negative charge transfer rate. Supported by the National Natural Science Foundation of China (Grant No. 50673069), the Research Foundation of Education Bureau of Sichuan Province, China (Grant No. 07ZA093), and Scientific Research Foundation of Sichuan Normal University for Innovation Groups ( Grant No. 025156)     

苯并菲盘状液晶的合成、亲氟效应及分子对称性对介晶性的影响

New symmetrical and asymmetrical triphenylene-containing discotic liquid crystals with two different peripheral alkyl chains, known as sym-TP(OC6H13)3(OR)3 and asym-TP(OC6H13)3(OR)3, were synthesized. Their thermotropic liquid crystal properties were investigated through polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The asyrranetdcal discogens are 2,6,11-rialkoxy-3,7,10-trihexyloxytriphenylenes, with the alkyl chain carbon numbers varying from 3-10, 12, and 14, while the symmetrical compounds are 2,6,10-trialkyloxy-3,7,11-trihexyloxytriphenylene. Two fluoroalkoxy substituted triphenylene discogens, 2,6,10-td(4,4,4-trifluorobutoxy)-3,7,11-trihexyloxytriphenylene and its asymmetrical isomer 2,6,11-tri(4,4,4-trifluorobutoxy)-3,7,10-trihexyloxytdphenylene were prepared. These two compounds show higher melting and clearing points than their alkoxy analogs, which implies that fluorophilic effect exists in the formation and stabilization of discotic columnar mesophase. The triphenylene derivatives TP(OC6H13)3(OR)3 with two different peripheral chains, symmetrically or asymmetrically attached on triphenylene cores, have lower melting points and clearing points than those of the higher symmetrical compounds TP(OR)6 with the same total chain carbon numbers. The mixed-chain-triphenylenes with longer alkoxy chains (n=9,10,12,14) show columnarmesophase at room temperature.     

Charge transport properties in discotic liquid crystals: a quantum-chemical insight into structure-property relationships

We describe at the quantum-chemical level the main parameters that control charge transport at the molecular scale in discotic liquid crystals. The focus is on stacks made of triphenylene, hexaazatriphenylene, hexaazatrinaphthylene, and hexabenzocoronene molecules and derivatives thereof. It is found that a subtle interplay between the chemical structure of the molecules and their relative positions within the stacks determines the charge transport properties; the molecular features required to promote high charge mobilities in discotic materials are established on the basis of the calculated structure-property relationships. We predict a significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique.     

Influence of branched chains on the mesomorphic properties of symmetrical and unsymmetrical triphenylene discotic liquid crystals

A series of novel symmetrical and unsymmetrical triphenylene‐based discotic liquid crystalline materials with one or six branched peripheral alkoxy chains have been prepared. These materials have been compared with analogous known symmetrical and unsymmetrical compounds to reveal a balance between steric and space‐filling effects of the peripheral branched chains, which significantly affects intermolecular forces of attraction and packing, and hence affects melting and isotropisation temperatures of the liquid crystalline materials. The desired result of reduction of melting points and enhancement of isotropisation temperatures has been accomplished by use of branched alkoxy chains in both symmetrical and unsymmetrical materials.     

δ‐Methyl Branching in the Side Chain Makes the Difference: Access to Room‐Temperature Discotics

Although discotic liquid crystals are attractive functional materials, their use in electronic devices is often restricted by high melting and clearing points. Among the promising candidates for applications are [15]crown‐5 ether‐based liquid crystals with peripheral n‐alkoxy side chains, which, however, still have melting points above room temperature. To overcome this problem, a series of o‐terphenyl and triphenylene [15]crown‐5 ether derivatives was prepared in which δ‐methyl‐branched alkoxy side chains of varying lengths substitute the peripheral linear alkoxy chains. The mesomorphic properties of the novel crown ethers were studied by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction. δ‐Methyl branching indeed lowers melting points resulting in room‐temperature hexagonal columnar mesophases. The mesophase widths, which ranged from 87 to 30 K for o‐terphenyls, significantly increased to 106–147 K for the triphenylenes depending on the chain lengths, revealing the beneficial effect of a flat mesogen, due to improved π–π interactions.     

Charge Transport through Peptides in Single‐Molecule Electrical Measurements

Charge transport across the peptide chains is one of the vital processes in the biological systems, so understanding their charge transport properties is an indispensable prerequisite to explain the complex biochemical phenomenon. Here, we review the charge transport mechanism, the influence of the special groups and the experimental conditions on the charge transport through the peptide backbone by employing the single‐molecule electrical measurements. Besides, we further review the recent progresses in charge transport properties of supramolecular interaction among the adjacent peptide chains. Finally, we discuss some experimental and theoretical contradictions existing in the charge transport through peptides and provide new inspiration for the future development of the bioelectronics at the single‐molecule scale.     

Alignment behaviour of symmetrical and asymmetrical triphenylenes possessing fluoroalkylated side chains on modified substrates

The alignment behaviour of triphenylene‐based compounds possessing fluoroalkylated and alkyl side chains was investigated for the hexagonal columnar (Col_h) mesophase on polyimide‐, cetyltrimethylammonium bromide (CTAB)‐, and indium tin oxide‐coated glass substrates by polarizing optical microscopy. It was found that 2,6,10‐trinonyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluorononyloxy)triphenylene and 2,6,11‐trinonyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluorononyloxy)triphenylene exhibit spontaneous homeotropic alignment on these substrates. On the other hand, it was found that 2,6,10‐triheptyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluoroheptyloxy)triphenylene, 2,6,11‐triheptyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluoroheptyloxy)triphenylene, 2,6,10‐trihexyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluorohexyloxy)triphenylene, 2,6,11‐trihexyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluorohexyloxy)triphenylene, 2,6,10‐tributyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluorobutyloxy)triphenylene and 2,6,11‐tributyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluorobutyloxy)triphenylene do not show such spontaneous homeotropic alignment on these substrates. These results indicate that the spontaneous homeotropic alignment of the Col_h phase could be easily attained by the introduction of an appropriate length of the fluoromethylene chains in the peripheral parts of discogens. Therefore, it is suggested that the balance between the hydrocarbon part including the triphenylene core and the fluoroalkyl part determines the alignment control behaviour. Furthermore, it was found that alignment behaviour is independent of the rotation symmetry of the chemical structure but is dependent on the number of fluoromethylene chains in the chemical structure.     

Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

Chlorination of π‐conjugated backbones is garnering great interest because of fine‐tuning electronic properties of conjugated materials for organic devices. Herein we report a synthesis of thiophene‐based diketopyrrolopyrrole (DPP) dimers and their chlorinated counterparts by introducing a chlorine atom in the outer thiophene ring to investigate the influence of the chlorination on charge transport. The backbone chlorination lowers both the HOMO and the LUMO of the dimers and leads to a blue‐shift of maximum absorption in compared to unsubstituted counterparts. X‐ray analysis reveals that the chlorine atom prompts the outer thiophene ring out of the planarity of the backbone with a relatively large torsional angle. The chlorinated dimers exhibit slipped one‐dimensional packing decorated with multiple intermolecular interactions, because of a combination of a negative inductive effect and a positive mesomeric effect of the halogen atom, which might facilitate charge transport within the oligomeric backbones. The mobility in the single‐crystal OFET devices of the chlorinated dimers is up to 1.5 cm² V^?1 s^?1, which is two times higher than that of the non‐chlorinated DPP dimers. Our results indicate that the chlorine atom plays a key role in directing non‐covalent interactions to lock the slipped stacks, enabling electronic coupling between adjacent molecules for efficient charge transport. In addition, our results also demonstrate that these DPP dimers with straight n‐octyl chains exhibit higher mobilities than the dimers with branched 2‐ethylhexyl chains.