Can octupolar molecules be poled by an external electric field?

Octupolar molecules are generally believed to be of potential use in developing nonlinear optical materials owing to the fact that they do not easily form molecular aggregates. This is often put against the conjectured drawback that electric fields have no poling, or ordering, effect for this class of molecules because of the lack of a permanent ground state dipole moment. In this paper, we analyze this notion in some detail and present results from molecular dynamics computer simulations of an ensemble of a prototypical octupolar molecule, the 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) molecule, dissolved in chloroform. It is found that TATB molecules indeed show rather significant dipole moments in solutions because of the dual action of the thermal motions of the atoms and the strong intermolecular interactions. Applied electric fields accordingly show significant effects on the orientations of the molecular dipole moments. We also find that TATB molecules can aggregate because of the strong hydrogen-bonding interactions between the molecules, though they lack a static permanent dipole moment. Thus, the simulation results for TATB molecules in solution present us with a totally different notion about the collective properties of octupolar molecules. Taking account of quantum chemistry results, we found that the collective molecular nonlinear optical (NLO) properties are enhanced after the onset of the electric field, showing significant anisotropic characteristics.     

Novel chiral conjugated macromolecules for potential electrical and optical applications

Optically active 1,1′‐binaphthyl molecules have been used to construct novel chiral dendrimers and linear polymers. Efficient light harvesting effects of the dendrimers have been observed. They have shown enantioselective fluorescence responses in the presence of chiral amino alcohol quenchers. They are potentially useful as fluorescent sensors for the recognition of chiral organic compounds. Linear binaphthyl polymers have shown strong light emitting properties. Their colors of emission can be systematically tuned by incorporating linkers of various conjugation length. A very efficient light emitting diode has been prepared from the binaphthyl‐based conjugated polymers. Nonlinear optical chromophores have been organized in the chiral binaphthyl polymer chains to construct noncentrosymmetric and multipolar materials. These novel propeller‐like polymers have shown significant second‐order nonlinear optical effects.     

Nonpolar second‐order nonlinear and electrooptic materials: Axially ordered chiral polymers and liquid crystals

This article reviews our work on the development and optimization of chiral, nonpolar media with large second‐order nonlinear optical responses. We show how molecular engineering, theory, and measurements can be used to optimize this promising class of nonlinear optical materials. We describe how supramolecular alignment into easily processable materials takes advantage of the relevant molecular hyperpolarizabilities. A wide variety of techniques can be used to fabricate bulk materials belonging to the chiral nonpolar symmetry groups, D_∞ and D₂. The microscopic chromophore alignment schemes that optimize the nonlinear optical response in such materials are deduced from general symmetry considerations for both molecules and bulk. We also speculate on the possible applications of such materials as image‐plane modulators. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2744–2754, 2003     

Theoretical Investigation on the Second-order Nonlinear Optical Properties of Chiral Amino Acid Zinc(Ⅱ) Porphyrins

Static second-order nonlinear optical effects of amino acid zinc(II) porphyrins 1, 2, 3 and 4 were calculated by the TDHF/PM3 method based on the molecular structures optimized at the semiempirical PM3 quantum chemistry level, showing due to the cancellation of symmetric center, these amino acid zinc(II) porphyrins exhibit second order nonlinear optical response. The analysis of β components indicated that these amino acid zinc(II) porphyrins are of multipolarizabilities, and they may be ascribed as the "mixture" of octupolar and dipoar molecules with ||βJ=3||/||βJ=1|| ≈ 5. It is found that there are no significant differences between the static β values of non-chiral and chiral amino acid zinc(II) porphyrins. However, the βxyz component, which is quite important to quadratic macroscopic х (2) susceptibility of chiral material, is increased significantly with the increase of side chain group of amino acids.     

Predication of second-order optical nonlinearity of [(Bu2t Im)AuX] (X=halogen) using time-dependent density-functional theory combined with sum-over-states method

The dipole polarizability and second-order polarizability of recently synthesized (1,3-di-ter-butylimidazol-2-ylidine) gold complexes [(Bu2t Im)AuX] (X=halogen) were investigated by using time-dependent density-functional theory combined with sum-over-states method. We have discovered that these complexes possess remarkably larger molecular second-order polarizability compared with the organometallic and organic complexes. The value of the second-order polarizability increases in the order of F相似文献   

Discotic liquid crystalline materials for potential nonlinear optical applications: synthesis and liquid crystalline behavior of 1,3,5-triphenyl-2,4,6-triazine derivatives containing achiral and chiral alkyl chains at the periphery

As a novel approach to nonlinear optical materials, new octupolar discotic liquid crystalline materials 1,3,5-triphenyl-2,4,6-triazine derivatives containing achiral alkyl chains (5a) and chiral alkyl chains (5b) at the periphery were synthesized. The former exhibits an ordered hexagonal columnar mesophase, whereas the latter displays a rectangular columnar mesophase. The negative exciton splitting observed in the CD spectrum of a thin film of 5b suggests that it has a left-handed helical structure within the column.     

Coherent Enantiomer‐Selective Population Enrichment Using Tailored Microwave Fields

We report the experimental demonstration of coherent enantiomer‐selective enrichment of chiral molecules by employing a novel microwave five‐pulse scheme. Our results show that enantiomers can be selectively transferred to a rotational level of choice by applying sequences of resonant microwave pulses in a phase‐ and polarization‐controlled manner. This is achieved by simultaneously exciting all three kinds of electric dipole‐allowed rotational transitions and monitoring the effect on a fourth rotational transition of choice. Using molecular beams, we apply our method to two chiral terpenes and obtain a 6 % enantiomeric enrichment, which is one order of magnitude larger than that recently reported in a buffer‐gas cell experiment. This approach establishes a robust scheme for controlled manipulation of enantiomers using tailored microwave fields and opens up new avenues for chiral purification and enrichment that can be used in a broad scope of analytical or spectroscopic applications.     

Quadrupole contribution to the third-order optical activity spectroscopy

Time-resolved nonlinear optical activity measurement spectroscopy can be a useful tool for studying biomolecular and chemical reaction dynamics of chiral molecules. Only recently, the two-dimensional (2D) circularly polarized photon echo (CP-PE) spectroscopy of polypeptides and a photosynthetic light-harvesting complex were discussed, where the beam configuration was specifically controlled in such a way to eliminate the quadrupole contribution to the CP-PE signal. In this paper, we generalize the CP-PE spectroscopy by including the transition quadrupole contributions from peptide amide I vibrational transition and chlorophyll electronic transition. By using a density functional theory calculation method, the corresponding amide I vibrational and chlorophyll Q(y) electronic transition quadrupole tensor elements are determined. Amplitude of nonlinear optical transition pathway involving a quadrupole transition is found to be comparable to those of magnetic dipole terms for two different cases considered, i.e., dipeptides and photosynthetic antenna complex. However, due to the rotational averaging factors, the overall quadrupole contribution is an order of magnitude smaller than the magnetic dipole contribution. This suggests that the conventional 2D photon echo method and experimental scheme can be directly used to measure the 2D CP-PE signal from proteins and molecular complexes and that the 2D CP-PE signal is mainly dictated by the magnetic dipole contribution.     

The interplay of bent-shape,lateral dipole and chirality in thiophene based di-, tri-, and tetracatenar liquid crystals

A range of mesogenic molecules varying in both bend angle and strength of lateral dipole were synthesized, and their phase behavior was characterized by polarizing microscopy, thermal analysis, X-ray diffraction, and electrooptical measurements. We find the general destabilization of the liquid crystallinity caused by strong lateral dipolar groups and the bent molecular shape are off-set in mesomorphic tetracatenars, which display stable nematic, smectic, columnar, and cubic mesophases. The broad mesomorphism of the tetracatenars containing lateral dipoles and their incompatibility with chiral induction are explained by considering that loosely correlated dimers exist within the mesophases. Chiral mesophases of derivatives with strong lateral dipoles were achieved by attaching fewer or different side chains to each end of the mesogen.     

A series of novel side chain liquid crystalline polysiloxanes containing cyano‐ and cholesterol‐terminated substituents: Where will the structure‐dependence of terminal behavior of the side chain reappear?

A series of polysiloxane side chain liquid crystal polymers with strong polarity cyano substitution‐terminated achiral side chains and cholesterol‐terminated chiral side chains was successfully synthesized via thiol‐ene click chemistry. ¹H‐NMR, FT‐IR, and thermogravimetric analysis were used to confirm their chemical structures and thermal stabilities. Their phase transition behaviors and phase structures were systematically investigated by a combination of analysis methods such as differential scanning calorimetry, polarized optical microscopy, and X‐ray. Results revealed that attributing to the decisive role of the polarity interaction, all the polymers only developed a monolayer interdigitated SmA phase in which the period arrangement was determined by the cyano‐terminated side chains, the increased content of cholesterol‐terminated chiral side chains (X_chol) just expanded the distance between neighboring molecules within a layer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1765–1772     

Influence of mesogenic core polarity and position of chains attachment on columnar phase stability

Series of new Ni(II) metalomesogens of triangular molecular shape and forming Col_h liquid crystalline (LC) phase were synthesised and described. Using in the molecular core the barbituric moieties that contain carbonyl or thiocarbonyl groups causes strong polarisation of the molecules and creates a permanent dipole moment μ, which was confirmed by quantum mechanical calculations. The relationship between molecular dipole moment and self-organisation of molecules into the columnar phase was considered. The position of alkyl and alkoxy chains substituted at phenyl ring that affects LC phase formation seems to be connected with planar conformation of the attached chains. These can broaden the mesogenic core and stabilise the Col_h mesophase.     

Synthesis and characterization of chiral compounds containing cationic groups as chiral dopants in liquid crystals

Novel chiral molecules containing cationic groups, (N-[4-triethylammoniomethyl]-benzoyl ester)-ethyl lactate chloride and bi-(N-[4-triethylammoniomethyl]-benzoyl ester)-isosorbide chloride, were designed and synthesized. Chemical structures of the molecules were characterized by elemental analysis, FT-IR, and (1)H NMR. The photochemical properties of the chiral compounds and their textures in nematic liquid crystals (LCs) were investigated by optical rotation, circular dichroism (CD), and polarizing optical microscopy (POM). The novel chiral molecules exhibited good optical activity. The chiral compound based on a L-ethyl lactate chiral center had a left-handed configuration. The chiral compound based on an isosorbide chiral center had a right-handed configuration. The cationic polar groups did not affect the direction of optical rotation, but could effluence the molar rotation of chiral compounds. The mixtures with dopants showed oily streak textures. Doping of a nematic phase liquid crystal with the chiral molecules converted it to the cholesteric phase.     

Nonlinear optical constants of polymers from molecular hyperpolarizabilities of donor–acceptor molecules

A mathematical analysis previously developed to solve the quadratic tensor equations that relate molecular hyperpolarizability and bulk medium nonlinear optical constants is applied to donor–acceptor polyene molecules. The focus is on mutual polarization of spatially organized collections of molecules, e.g., chromophore side chains in an optical polymer. The performance of the electrostatic model is first confirmed by comparison with MOPAC calculations of composite molecules containing a pair of chromophores, and then applied to linear polymer chains as well as lattices in two and three dimensions. An optimal chromophore packing density is determined to maximize the macroscopic susceptibilities of polymer materials of the type studied. This is lower than the density allowed by the structure of the polymer, because of the mutual depolarization of chromophores at high packing densities. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

含有噻唑生色团的Y-型有机分子的二阶非线性光学性质

采用密度泛函理论(DFT)B3LYP/6-31G*方法优化了一系列含有噻唑生色团的Y-型有机杂环分子的几何构型, 在此基础上结合有限场(FF)方法和含时密度泛函理论(TD-DFT)对分子的非线性光学(NLO)活性和电子光谱进行计算分析. 结果表明, 这些分子具有A-π-D-π-A(A: 受体, D: 给体)结构, 分子基态偶极矩、极化率和二阶NLO系数(β)随支链共轭桥的增长及生色团共轭效应的增大而增大. 同时, 该系列有机杂环分子的二阶极化率总的有效值(βtot)与其前线分子轨道能级相关, 分子的前线分子轨道能级差越小, βtot值越大.     

非线性光学材料的分子设计研究

非线性光学研究应用电磁场和各种材料的相互作用, 产生新的电磁场, 改变频率, 相或其它物理性质. 本文介绍了非线性光学材料分子设计的原理, 并以共轭长链分子和碳笼及其衍生物为例报道了我们在这方面的研究工作.     

Dynamic Supramolecular Polymers Based on Benzene‐1,3,5‐tricarboxamides: The Influence of Amide Connectivity on Aggregate Stability and Amplification of Chirality

N‐Centred benzene‐1,3,5‐tricarboxamides (N‐BTAs) composed of chiral and achiral alkyl substituents were synthesised and their solid‐state behaviour and self‐assembly in dilute alkane solutions were investigated. A combination of differential scanning calorimetry (DSC), polarisation optical microscopy (POM) and X‐ray diffraction revealed that the chiral N‐BTA derivatives with branched 3,7‐dimethyloctanoyl chains were liquid crystalline and the mesophase was assigned as Col_ho. In contrast, N‐BTA derivatives with linear tetradecanoyl or octanoyl chains lacked a mesophase and were obtained as crystalline compounds. Variable‐temperature infrared spectroscopy showed the presence of threefold, intermolecular hydrogen bonding between neighbouring molecules in the mesophase of the chiral N‐BTAs. In the crystalline state at room temperature a more complicated packing between the molecules was observed. Ultraviolet and circular dichroism spectroscopy on dilute solutions of N‐BTAs revealed a cooperative self‐assembly behaviour of the N‐BTA molecules into supramolecular polymers with preferred helicity when chiral alkyl chains were present. Both the sergeants‐and‐soldiers as well as the majority‐rules principles were operative in stacks of N‐BTAs. In fact, the self‐assembly of N‐BTAs resembles closely that of their carbonyl (C?O)‐centred counterparts, with the exception that aggregation is weaker and amplification of chirality is less pronounced. The differences in the self‐assembly of N‐ and C?O‐BTAs were analysed by density functional theory (DFT) calculations. These reveal a substantially lower interaction energy between the monomeric units in the supramolecular polymers of N‐BTAs. The lower interaction energy is due to the higher energy penalty for rotation around the Ph? NH bond compared to the Ph? CO bond and the diminished magnitude of dipole–dipole interactions. Finally, we observed that mixed stacks are formed in dilute solution when mixing N‐BTAs and C?O BTAs.     

手性锌卟啉的非线性光学性质及对咪唑类客体分子识别的构象研究

在纳秒(ns)领域中，利用Z-扫描技术测定了Zn(o-BocTyr)TAPP(主体1)和Zn(p-BocTyr)TAPP(主体2)两种手性锌卟啉的三阶非线性光学性质以及对咪唑类客体的分子识别行为的构象研究. 结果表明，(1) 两种手性锌卟啉都具有反饱和吸收效应和自散焦效应；(2) 由于两种主体中侧链位置的差异，造成两种主体分子极化程度的不同，主体1具有较大的三阶非线性折射率(n2)值；(3) 主体1中侧链苯环与卟啉环之间存在一定的相互作用；(4) 分子识别出现了配位方向的选择性，客体咪唑(Im)与主体1侧链中的苯环能够形成π-π相互作用，选择从有侧链一方配位于主体1，而2-甲基咪唑(2-MeIm)选择从没有侧链一方进攻主体1，但对于主体2，则没有出现配位方向的选择性.     

Molecular origins of the remarkable chiral sensitivity of second-order nonlinear optics.

Recent observations of remarkably large chiroptical effects in second-harmonic generation (SHG) and sum-frequency generation (SFG) measurements suggest exciting possibilities for the development of new chiral-specific spectroscopies and novel chiral materials for nonlinear optics. Several fundamental studies designed to elucidate the molecular and macromolecular origins of the chiral responses are reviewed to provide a framework for development of this emerging field. In general, the chiral activity in SHG and SFG has the potential to arise from complex interactions between hosts of different competing effects. Fortunately, relatively simple electric dipole-allowed mechanisms routinely dominate the nonlinear optical chiral activities of most practical systemsexpressions can often be generated to link the. This substantial reduction in complexity allows for the development of simple models connecting the macroscopic nonlinear optical response to intuitive molecular and supramolecular properties.     

六元碳环邻位对称取代的Λ-型分子非线性光学系数的计算

采用密度泛函理论(DFT)的BHandHLYP/6-31G*方法,对3类含有六元碳环的Λ-型分子的几何构型进行优化.在优化结构的基础上,结合有限场方法(FF)和含时密度泛函理论(TD-DFT)对分子的二阶非线性光学(NLO)活性及电子吸收光谱进行研究.结果表明,在拐点处环己烷的构象不同时,分子电荷分布、偶极矩、极化率、二阶NLO系数和电子吸收光谱等变化很小.以苯环为拐点片段的分子有所不同,当支链取代基R增大时,以苯环为拐点片段分子的极化率和二阶NLO系数增加明显.     

Optical manipulation with nanoscale chiral fields and related photochemical phenomena

Chiral light-matter interaction occurs when the system consists of the matter and the light has a chiral structure, which is generically called the chiro-optical effect. Circular dichroism and optical rotation are representative spectroscopic methods based on chiro-optical effects. Chiro-optical effects have been widely utilized to detect chiral materials in the system. The chiro-optical effect also has the potential to create chiral materials from achiral materials and chiral optical fields, and to generate chiral optical fields from chiral matter systems. To achieve that, the design and observation of chiral optical field structures are essential. In this article, we describe local chiral optical fields generated in the peripheries of nanomaterials (typically metal nanostructures) irradiated with light. We summarize basic characteristics of nanoscale local chiral optical fields, methods to observe/control the chiral optical field structures at nanomaterials. Then some chemical, optical, and mechanical effects of designed chiral optical fields are described. Chiral nanostructures were created from achiral nanomaterials combined with circularly polarized light. Nucleation of chiral crystals of achiral molecules was achieved by circularly polarized light with the aid of plasmonic materials. Circularly polarized luminescence was observed from achiral fluorescent molecules conjugated with chiral plasmonic nanostructures. On mechanical characteristics, optical forces exerted on chiral materials were found to be dependent on the handedness of incident circularly polarized light, which can be utilized to discriminate the chirality of the material. The concept can be further generalized to the spin-dependent asymmetric light-matter interactions, which will create not only the molecular- and nano-scale chiral structures but also various novel functions of materials that are correlated with the handedness degree of freedom.