全椅式边含薁缺陷石墨烯纳米片的二阶非线性光学性质

基于全椅式边石墨烯纳米片(GNSs), 在保证GNSs化学稳定性的前提下并考虑了纳米片形状(六边形、 三角形和平行四边形), 在全椅式边GNSs中分别引入2, 3和4个薁构成的常见本征缺陷来调节这些GNSs的二阶非线性光学性质. 研究结果表明, 薁缺陷数量对于这些GNSs的二阶非线性光学响应起主导作用. 含有4个薁缺陷的GNSs具有较大的二阶非线性光学响应, 其中AP-4a纳米片具有最大的静态第一超极化率(<β₀>,230387.70 a. u., 平均每个重原子的<β₀>为2260.42 a. u.). 纳米片形状对体系的二阶非线性光学响应也有一定的影响. 薁单元片段在GNSs中不仅诱导GNSs发生电荷分布极化, 而且还在对非线性光学响应起重要贡献的主要电子跃迁中起主要作用. 薁单元作为碳基纳米材料的功能单元极大改善了其光电性质.     

Theoretical Studies on the Electronic Structure of Nano-graphenes for Applications in Nonlinear Optics

In this work, azulene is introduced into nano-graphene with coronene center to enhance the second-order nonlinear optical (NLO) properties. The sum-over-states(SOS) model based calculations demonstrate that dipolar contributions are larger than octupolar contributions to the static first hyperpolarizability(〈β₀〉) in most nano-graphenes except those with high symmetry(e.g., a C_2v nano-graphene has octupolar contributions Φ^J=3 up to 59.0% of the 〈β₀〉). Nano-graphenes containing two parallel orientating azulenes (i.e., Out-P and Out-P_s) have large dipole moments, while their ground state is triplet. Introducing B/N/BN atoms into the positions with a high spin density transfers the ground state of Out-P and Out-P_s to closed-shell singlet, and the Out-P_s-2N has a large 〈β₀〉 of 1621.67×10⁻³⁰ esu. Further addition of an electron donor(NH₂) at the pentagon end enhances the 〈β₀〉 to 1906.22×10⁻³⁰ esu. The two-dimensional second-order NLO spectra predicted by using the SOS model find strong sum frequency generations and difference frequency generations, especially in the near-infrared and visible regions. The strategies to stabilize the electronic structure and improve the NLO properties of azulene-defect carbon nanomaterials are proposed, and those strategies to engineer nano-graphenes to be semiconducting while maintaining the π-framework are exten-dable to other similar systems.     

Theoretical studies of third-order nonlinear optical response for B12N12, B24N24 and B36N36 clusters

In this paper, we have calculated the third-order nonlinear optical polarizabilities corresponding to three optical processes: third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) for B₁₂N₁₂, B₂₄N₂₄ and B₃₆N₃₆ clusters. The calculations have been performed by employing ab initio time-dependent density functional theory combined with sum-over-states method (SOS//TDDFT). We obtained the similar dynamic behavior of third-order NLO polarizabilities for three BN clusters. At input photon energy below 1.25 eV, the resonance enhancements of response haven't occurred. This is due to the fact that the calculated BN clusters have the large transition energy. B₂₄N₂₄ cluster has the larger transition dipole moments and the third-order polarizabilities of B₂₄N₂₄ are much larger than those of B₁₂N₁₂ and B₃₆N₃₆. We also estimate the static third-order optical susceptibility χ⁽³⁾ for BN fullerene materials from the average static third-order polarizability <γ>. The static χ⁽³⁾ of B₂₄N₂₄ fullerene materials are 1.36×10⁻¹⁴ esu for three NLO processes.     

Helical Nanographenes Containing an Azulene Unit: Synthesis,Crystal Structures,and Properties

Three unprecedented helical nanographenes ( 1 , 2 , and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X-ray crystallographic analysis. The embedded azulene unit in 2 possesses a record-high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis-spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps ( 2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in-situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties.     

Helical Nanographenes Containing an Azulene Unit: Synthesis,Crystal Structures,and Properties

Three unprecedented helical nanographenes ( 1 , 2 , and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X‐ray crystallographic analysis. The embedded azulene unit in 2 possesses a record‐high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis‐spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps ( 2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in‐situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties.     

Controlled plasmon resonance properties of hollow gold nanosphere aggregates

Hollow gold nanospheres (HGNs) ranging from 29.9 nm/8.5 nm (outer diameter/shell thickness) to 51.5 nm/4.5 nm and having aspect ratios spanning 3.5-11.7 were employed to investigate the ability to tailor charge oscillations of HGN aggregates by systematic variation of particle aspect ratio, interparticle gap, and nanosphere inner surface spatial separation. Altering these properties in aggregated HGNs led to control over the interparticle plasmon resonance. Thiol-mediated aggregation was accomplished using either ethanedithiol or cysteine, resulting in dimeric structures in which monomer subunits were spatially separated by <3 ? and 1.2 ± 0.7 nm, respectively. Particle dimensions and separation distances were confirmed by transmission electron microscopy. Experimental absorption spectra obtained for high-aspect ratio nanospheres dimerized using ethanedithiol exhibited an obvious blue shift of the surface plasmon resonance (SPR) relative to that observed for the native, monomeric HGN. This spectral difference likely results from a charge-transfer plasmon resonance at the dimer interface. The extent of the blue shift was dependent upon shell thickness. Dimers comprised of thin-shelled HGNs exhibited the largest shift; aggregates containing HGNs with thick shells (≥7 nm) did not display a significant SPR shift when the individual particles were in contact. By comparison, all cysteine-induced aggregates examined in this study displayed large interparticle gaps (>1 nm) and a red-shifted SPR, regardless of particle dimensions. This effect can be described fully by a surface mode coupling model. All experimental measurements were verified by finite difference time domain calculations. In addition, simulated electric field maps highlighted the importance of the inner HGN surface in the interparticle coupling mechanism. These findings, which describe structure-dependent SPR properties, may be significant for applications derived from the plasmonic nanostructure platform.     

Sensing behavior of BN nanosheet toward nitrous oxide: A DFT study

In order to develop a sensor for the detection of toxic N₂O molecules, the interaction of pristine and Aldoped BN nanosheets with an N₂O molecule was investigated using density functional theory calculations. It was found that unlike the pristine sheet, the Al-doped sheet can effectively interact with the N₂O molecule so that its electronic properties and conductivity are dramatically changed. Webelieve that replacing a B atom of the BN sheet with an Al atom may be a good strategy for improving the sensitivity of these nanosheets toward N₂O, which cannot be trapped and detected by the pristine sheet.     

Azulene-based organic functional molecules for optoelectronics

Design and synthesis of new organic functional materials with improved performance or novel properties are of great importance in the field of optoelectronics. Azulene, as a non-alternant aromatic hydrocarbon, has attracted rising attention in the last few years. Different from most common aromatic hydrocarbons, azulene has unique characteristics, including large dipole moment, small gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). However, the design and synthesis of azulene-based functional materials are still facing several challenges. This review focuses on the recent development of organic functional materials employing azulene unit. The synthesis of various functionalized azulene derivatives is summarized and their applications in optoelectronics are discussed, with particular attention to the fields including nonlinear optics (NLO), organic field-effect transistors (OFETs), solar cells, and molecular devices.     

Enhancement of the thermal and mechanical properties of a surface‐modified boron nitride–polyurethane composite

Thermoplastic polyurethane (PU) elastomer, prepared from poly(tetramethylene glycol) and methyl diphenyl diisocyanate, was blended with boron nitride (BN) to fabricate a thermally conductive interface material. BN treated by a silane coupling agent (BN―NH₂) and PU‐grafted BN were prepared to fabricate a composite that has better thermal conductivity and mechanical strength. The surface‐modified filler showed enhanced dispersibility and affinity because of the surface treatment with functional groups that affected the surface free energy, along with the structural similarity of the doped crystallized diisocyanate molecule with the matrix. The thermal conductivity increased from 0.349 to 0.467 W mk^?1 on 20 wt% PU‐grafted BN loading that is a 1.34‐fold higher value than in the case of pristine BN loading at the same weight fraction. Moreover, the number of BN particles acting as defects, thereby reducing the mechanical strength, is decreased because of strong adhesion. We can conclude that these composite materials may be promising materials for a significant performance improvement in terms of both the thermal and mechanical properties of PU‐based polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Strongly non-linear optical ferroelectric liquid crystals for frequency doubling

From our research for novel non-linear optical (NLO) materials for frequency doublers and optical modulators we report on new ferroelectric liquid crystals, which for the first time, exhibit second order NLO coefficients (for example d₂₂ = 5 pm V^-1, which are comparable to those of state of the art inorganic NLO materials. The novel compounds contain 5-amino-2-nitrophenyl groups attached close to the chiral centres. The switching behaviour of the new compounds, their spontaneous polarization, as well as their frequency doubling of Nd:YAG laser pulses in the S*_c and in the glass state, are reported. Moreover their waveguiding properties are presented.     

Solvent induced enhancement of nonlinear optical response of graphdiyne

Flat and crystalline materials with exceptional nonlinear optical(NLO) properties are highly desirable for their potential applications in integrated NLO photonic devices.Graphdiyne(GD),a new twodimensional(2 D) carbon allotrope,has recently evoked burgeoning research attention by virtue of its tunable bandgap along with a high carrier mobility and extended π-conjugation compared with most conventional optical materials.Here,we experimentally probe the third-order nonlinear optical response of GD dispersed in several common solvents(alcohols) using a femtosecond Z-scan technique.The measured nonlinear optical refractive index is in the order of ~10^-8 cm²/W,which is approximately one order of magnitude higher than that of most 2 D materials.In particular,we find that different NLO responses can be observed from GD when dispersed in different solvents,with the strongest NLO response when dispersed in 1-propanol.It is proposed that some intrinsic properties of the solvents,such as the polarity and viscosity,could influence the NLO response of GD materials.Our experimental results confirm the assumptions on the NLO behavior in GD and demonstrate its great potential for future generations of Kerr-effect-based NLO materials and devices.     

Preparation of silica-encapsulated hollow gold nanosphere tags using layer-by-layer method for multiplex surface-enhanced raman scattering detection

The use of silica shells offers many advantages in surface-enhanced Raman scattering (SERS)-based biological sensing applications due to their optical transparency, remarkable stability in environmental media, and improved biocompatibility. Here, we report a novel layer-by-layer method for the preparation of silica-hollow gold nanosphere (HGN) SERS tags. Poly(acrylic acid) was used to stabilize Raman reporter-tagged HGNs prior to the adsorption of a coupling agent, after which a silica shell was deposited onto the particle surface using Sto?ber's method. Importantly, competitive adsorption of the Raman reporter molecules and coupling agents, which results in unbalanced loading of reporter molecules on individual nanoparticles, was avoided using this method. As a result, the loading density of reporter molecules could be maximized. In addition, HGNs exhibited strong enhancement effects from the individual particles because of their ability to localize the surface electromagnetic fields through pinholes in the hollow particle structures. The proposed layer-by-layer silica-encapsulated HGN tags showed strong SERS signals as well as excellent multiplexing capabilities.     

杂原子掺杂的含单空位缺陷BN纳米管的非线性光学性质

采用密度泛函理论(DFT)研究了杂原子M(M=Li, Na, K, Be, Mg, Ca, C和Si)在B/N单空位缺陷处的掺杂对(6,0)BN纳米管体系非线性光学性质的影响. 采用B3LYP方法共得到了14种几何构型, 并采用BHandHLYP方法计算了这些结构的第一超极化率β₀值. 研究结果表明, 单纯的B或N缺陷几乎不影响BN纳米管体系的非线性光学性质; 与B缺陷处掺杂的体系相比, 杂原子在N缺陷处的掺杂更有利于提高BN纳米管体系的第一超极化率β₀值; 对于同周期掺杂原子, 还原性越强的原子掺杂对BN纳米管体系的第一超极化率β₀值的改善越明显, 表现为β₀(Ⅰ族)>β₀(Ⅱ族)>β₀(Ⅳ族); 对比同主族掺杂原子, 第三周期元素Na和Mg的掺杂能更有效地提高体系的第一超极化率β₀值, 原因主要在于原子半径和还原性等因素共同决定其对BN纳米管体系第一超极化率β₀值的改善程度. 本文研究结果为有效提高BN纳米管体系的非线性光学性质提供了一种新思路, 为基于BN纳米管的非线性光学材料设计提供了有价值的理论信息.     

卟啉-碳硼烷-硼亚甲基二吡咯三元化合物二阶非线性光学性质的理论研究

采用密度泛函理论(DFT)方法对卟啉-碳硼烷-硼亚甲基二吡咯(BODIPY)三元化合物的几何结构、 吸收光谱及二阶非线性光学(NLO)特性进行计算分析. 结果表明, V型化合物的静态第一超极化率(β_tot)大于相应直线型化合物, 且延长共轭链可提高体系的β_tot. 分析体系的电子密度差分图得出, 化合物氧化还原态的电荷转移方式与本征态相比发生了改变, 从而使其二阶NLO性质发生明显变化. 含频第一超极化率计算结果表明, 在一定范围内频率对化合物有较小的色散效应. 因此, 通过延长二维化合物的共轭链及氧化还原反应, 可以有效调控其二阶NLO响应.     

脂环酮均相催化硅氢化反应的研究

以(Ph₃P)₃RhCl作催化剂.苯为介质,利用原位傅立叶红外光谱技术和假一级动力学方法,对脂环酮的均相催化硅氢化反应进行了研究,考查了脂环嗣环及环硅氢化物环的大小对反应速率的影响,结果表明其活性顺序为:模型反应I:k₄>k₆>k₅>k₇;模型反应Ⅱ:k₅>k₅.提出了硅基对环酮羰基的迁移插入为反应的决定速率步骤.     

Stable second‐order NLO semi‐IPN system based on bipyridine‐containing polyimide and alkoxysilane dye

An organosoluble polyimide based on bipyridyl moiety and an alkoxysilane dye have been developed for second‐order non‐linear optics (NLOs). This bipyridine‐containing polyimide exhibits a glass transition temperature of 254°C and a degradation temperature of 400°C. An NLO‐active semi‐interpenetrating network (IPN) system was prepared by blending the polyimide with the alkoxysilane dye via in situ sol‐gel process of alkoxysilane. The selection of this bipyridine‐containing polyimide as the polymeric matrices provides improved solubility and thermal stability, and most importantly enhanced intermolecular interactions. No aggregation of the NLO chromophores in the polyimide matrices was observed through morphology and NLO studies. Under the limitation of chromophore degradation at elevated temperatures, the pristine poled/cured alkoxysilane dye exhibits poorer long‐term stability. By introducing the polyimide upon a silica network by the semi‐IPN system, randomization of the oriented chromophores can be effectively suppressed. Using in situ contact poling, the r₃₃ coefficients of 2.2–17.0 pm/V were obtained for the optically clear semi‐IPN NLO materials. Excellent temporal stability (100°C) was also achieved for these semi‐IPN materials. Copyright © 2005 John Wiley & Sons, Ltd.     

Relative quantum yield of the S2 → S1 fluorescence from azulene

The quantum yield ratio r = φ_{2 → 0}/φ_{2 → 1} of the S₂ → S₀ and S₂ → S₁ fluorescences from azulene has been redetermined. With azulene in isopentane at 190 K, r = 455 ± 100. This value agrees with the lower limit, given by Huppert, Jortner and Rentzepis, but is an order of magnitude lower than that given by Gillispie and Lim.     

Metal oxyhalides: an emerging family of nonlinear optical materials

Second-order nonlinear optical (NLO) materials have drawn enormous academic and technological attention attributable to their indispensable role in laser frequency conversion and other greatly facilitated applications. The exploration of new NLO materials with high performances thus has long been an intriguing research field for chemists and material scientists. However, an ideal NLO material should simultaneously satisfy quite a few fundamental yet rigorous criteria including a noncentrosymmetric structure, large NLO coefficients, desired transparent range, large birefringence, high laser damage threshold, and availability of a large-size single crystal. Therefore, the identification of promising compound systems, targeted design, and experience-based syntheses are crucial to discover novel NLO materials working in the spectral region of interest. As an important family of mixed-anion compounds, versatile metal oxyhalides containing metal-centered oxyhalide functional units ([MO_mX_n] (X = F, Cl, Br, and I)) are becoming a marvelous branch for interesting NLO materials. Especially, when the central metals are d⁰/d¹⁰ transition metals or heavy post-transition metals, a number of novel NLO materials with superior functionalities are expected. Our thorough review on the recent achievements of metal oxyhalides for NLO materials are divided into the fast-growing NLO metal oxyhalides with single type halogen anions and the newly identified NLO metal oxyhalides with mixed halogen anions. Here we mainly focus on the design strategy, structural chemistry, NLO-related properties, and structure–property correlation of the metal oxyhalides with relatively large NLO responses. We hope this review can provide an insight on the rational design and future development of emerging metal oxyhalides for NLO and other applications.

Nonlinear optical metal oxyhalides could provide a new insight into the target design and exploratory synthesis of new functional materials with intriguing chemical and physical properties.     

Theoretical study on second‐order nonlinear optical properties of spin crossover Fe(III) phenolate‐pyridyl Schiff base complexes

The density functional and ab initio theory were used to investigate the second‐order nonlinear optical (NLO) properties of Schiff base ligands, open‐shell Fe(III), and closed‐shell Ni(II) complexes. The effect of the metal center in complexes is thus manifold: it templates the formation of acentric structures, imparts high thermal stability to the chelate ring, and display higher second‐order NLO response than their ligands. The second‐order NLO response of metal complexes are intensively sensitive to the exchange donor/acceptor because the differences of the extent of charge separation and the intraligand charge transfer processes. Thus, substituted metal complexes could realize “switches on” the second‐order NLO response by exchange donor/acceptor. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Synthesis, characterization, and tunable optical properties of hollow gold nanospheres

Nearly monodisperse hollow gold nanospheres (HGNs) with tunable interior and exterior diameters have been synthesized by sacrificial galvanic replacement of cobalt nanoparticles. It is possible to tune the peak of the surface plasmon band absorption between 550 and 820 nm by carefully controlling particle size and wall thickness. Cobalt particle size is tunable by simultaneously changing the concentration of sodium borohydride and sodium citrate, the reducing and capping agent, respectively. The thickness of the gold shell can be varied by carefully controlling the addition of gold salt. With successful demonstration of ensemble as well as single HGN surface-enhanced Raman scattering, these HGNs have shown great potential for chemical and biological sensing applications, especially those requiring nanostructures with near-IR absorption.