Preparation and nonlinear optical properties of inorganic-organic hybrid films with various substituents on chromophores

Four kinds of hydroxy-ended azobenzene-type chromophores containing different substituent groups as electron donor or electron acceptor were synthesized and further reacted with 3-isocyanatopropyltriethoxysilane (ICTES) to give alkoxysilane dyes via a urethane reaction. Following a sol-gel process of the alkoxysilane dyes, the inorganic-organic hybrid nonlinear optical (NLO) films were successfully prepared. Molecular structures of the resultant films were confirmed by elemental analysis, FTIR, and 1H NMR. The betaCT mu(g) values of the chromophores were evaluated by a solvatochromic method, and the second harmonic coefficients (d33) of the hybrid films were measured by in situ second harmonic generation (SHG) measurement. The hybrid films exhibited large optical nonlinearity and full transparency in the visible range. The effects of substituent group and position on betaCT mu(g) values of the chromophores and d33 values of the films were also discussed.     

Inorganic-organic hybrid nonlinear optical films containing bulky alkoxysilane dyes

Two bulky alkoxysilane dyes based on nonlinear optical (NLO)-active triphenylamino derivatives possessing high thermal stabilities, without and with a cyano group substitution on the vinylene moiety (TPAH and TPACN, respectively), were synthesized, characterized, and copolymerized with tetraalkoxysilane (TEOS) with the ratio of 1:5. After a poling and curing process, the resulting side-chain-type sol-gel films with excellent optical qualities were achieved. Second-order NLO coefficients, d33, of 10-20 pm/V have been obtained in the films incorporated with different types of NLO-active dyes. The variation of chromophoric structures on NLO properties was investigated, indicating that the cyano substitution on the vinylene bridge of the chromophore would greatly enhance the temporal stability. This work provides a potential design strategy based on molecular engineering which would lead to more stable dipole orientation.     

含对硝基偶氮苯胺生色团的键合型有机/无机复合材料的合成及其二阶非线性光学特性

以γ 缩水甘油氧丙基三甲氧基硅烷 (KH5 6 0 )作中间体 ,用溶胶 凝胶 (Sol Gel)法合成了含对硝基偶氮苯胺 (DO3)生色团的新型键合型有机 /无机复合非线性光学 (NLO)材料 ,在这种有机生色团与无机玻璃键合形成的交联网络结构中 ,无机玻璃的刚性三维结构和优良的高温稳定性能有效抑制NLO生色团的极化松弛 .二次谐波信号 (SHG)测量表明 ,合成的键合型聚合物膜的二阶非线性光学系数 (d33)值达 5 79× 10 -7esu ,NLO稳定性也较好 ;在室温下放置 90天后 ,其d33 值能维持初始值的 93 5 % ;在 10 0℃下放置 30 0min后 ,其d33 值仍能维持初始值的 6 0 %     

Dipolar orientation stabilities of hybrid films for second-order nonlinear optical applications

Organic–inorganic hybrid films containing nonlinear optical (NLO) active chromophores were prepared through the polyaddition of methacrylate and hydrolytic polycondensation of sila-functional alkoxy groups of 3-(trimethoxysilyl)propyl methacrylate (TSPM) which is capable of forming carbon–carbon and siloxane chains, respectively. The NLO-active chromophores are designed and synthesized to be covalently grafted to the carbon–carbon or the siloxane chains. The comparative study of the two different incorporation methods reveals that the poled hybrid film with NLO-active chromophores bonded to siloxane chains would possess a more stable dipolar orientation.     

聚酰亚胺多层膜的制备及其在非线性光学中的应用

报道了一种通过旋涂制备NLO聚合物多层膜的方法.紫外-可见吸收光谱及膜的厚度表征说明,在所得多层膜的结构中,聚合物单层膜的厚度可以较好地控制在100~200nm之间,所得含有5个双层的NLO多层膜(厚度1.6μm)具有良好的结构均一性,光学显微镜下没有观察到明显的结构缺陷.与单层具有较大厚度的NLO聚合物薄膜(如2~4μm)相比,所得聚合物多层膜可以允许掺杂更多的发色团而不发生相分离.     

Challenging the auxiliary donor effect on molecular hyperpolarizability in thiophene-containing nonlinear chromophores: X-ray crystallographic and optical measurements on two new isomeric chromophores

To reexamine the established "auxiliary donor" effect of thiophene in nonlinear optical (NLO) chromophores, we have prepared two isomeric donor-acceptor azo dyes, differing only in the position of the thiophene. Experimental analysis of these chromophores, including electric field-induced second harmonic generation (EFISH) and X-ray crystallography, contradicts previous experimental findings on similar chromophores but is consistent with the majority of computational precedents. We have found that the thiophene on the donor side produces a compound with a larger dipole moment; however, the isomer with the thiophene on the acceptor side is more nonlinear and has a higher figure of merit for NLO device applications.     

From controllable attached isolation moieties to possibly highly efficient nonlinear optical main-chain polyurethanes containing indole-based chromophores

For the first time, the indole-based NLO chromophores were embedded into the polymer main chain, and different isolation groups were attached to their donor side with the efforts of adjusting the NLO properties of the resultant main-chain polyurethanes, according to the site isolation principle. Thanks to the main-chain structure and the advantages of the indole-based chromophores, all the polymers show excellent transparency, good processability, thermal stability, and relatively good NLO effects. The tested NLO properties of the polymers demonstrate that there is a suitable isolation group present for the sulfonyl-based chromophore to boost its microscopic beta value to a possibly higher macroscopic NLO property efficiently.     

基于分子间侧向氢键作用的电光材料制备及性能

通过重氮耦合和酯化等反应制备了一系列侧向含有酰胺基团的偶氮苯类非线性光学生色团, 并将其与聚合物进行掺杂或通过分子间的侧向氢键作用制备了主客体型及超分子型的电光薄膜材料. 生色团的结构通过核磁共振谱(¹H NMR, NMR)、 红外光谱(IR)、 质谱(MS)和元素分析(EA)等进行了表征, 结果表明, 生色团形成了分子间的氢键作用. 通过紫外-可见(UV-Vis) 光谱研究了材料的极化性能. 相比主客体型电光薄膜材料, 由分子间侧向氢键作用形成的超分子型电光薄膜材料无需与聚合物基体材料复合, 更有利于提高材料的生色团含量、 极化取向度及稳定性. 通过Teng-Man简单反射法研究了主客体型和超分子型电光材料的二阶非线性光学性质, 结果表明, 基于分子间侧向氢键作用形成的超分子体系具有更大的电光系数.     

PREPARATION AND SECOND-ORDER OPTICAL NONLINEARITY OF NOVEL PHENOXYSILICON NETWORKS BY SOL-GEL PROCESS**

 Four phenoxysilicon networks for nonlinear optical (NLO) applications were designed and prepared by an extended sol-gel process without additional H₂O and catalyst. All poled polymer network films possess high second-order nonlinear optical coefficients (d₃₃) of 10-?～10-8 esu. The investigation of NLO temporal stability at room temperature and elevated temperature (120℃) indicated that these films exhibit high d33 stability because the orientation of the chromophores are locked in the phenoxysilicon organic/inorganic networks.     

Synthesis and second-order nonlinear optical properties of new chromophores containing benzimidazole, thiophene, and pyrrole heterocycles

A new series of thermally stable benzimidazole-based nonlinear optical (NLO) chromophores 4 and 5 have been developed. These chromophores possess a thienylpyrrolyl π-conjugated system attached to functionalized benzimidazole heterocycles. This feature leads to robust chromophores with excellent solvatochromic properties, high thermal stabilities and good molecular optical nonlinearities.     

Effect of pendant group on the second-order optical nonlinearity of sol–gel films

A series of organically modified sol–gel films with various acceptor groups were prepared and characterized. All the chromophores exhibit much larger microscopic optical nonlinearity compared with the classical chromophore DR1 in solvatochromic measurement. Using in situ second harmonic generation (SHG) technique, the optimal poling temperatures (T _opt) for sol–gel films were obtained. The second harmonic coefficients (d ₃₃) of hybrid films at the wavelength of 1,064 nm were in the range of 50.1–70.3 pm/V after corona poling under their T _opt. The NLO stabilities of these poled films were also investigated by tracing the d ₃₃ value as a function of temperature and time. One of the hybrid films, which was prepared from chromophore 2,4-dinitro-4′-(N,N-dihydroxyethyl) aminoazobenzene exhibited a combination of large optical nonlinearity and high NLO stability. Furthermore, the effects of molecular structure on the NLO property and thermal stability of the hybrid films were also discussed.     

Synthesis of nonlinear optical polyimides containing azodiamine derivative chromophores and their electrooptic and thermal properties

Some thermally stable second‐order nonlinear optical (NLO) polyimides were synthesized. The polyimides were prepared by the ring‐opening polyaddition of 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride and pyromellitic dianhydride with two aromatic azodiamine derivatives as the NLO chromophores. These chromophores, based on a nitro group connected with azobenzene as the acceptor end of a donor–π‐bridge–acceptor chromophore and a diamine group as the donor end, had specific chemical stability. On the basis of ZERNER'S INDO methods, according to the sum‐over‐states formula, a program for the calculation of nonlinear second‐order optical susceptibilities was devised. The resulting polyimides had high number‐average and weight‐average molecular weights of up to 26,000 and 53,500, respectively, and a large glass‐transition temperature of 248 °C. With an in situ poling and temperature ramping technique, the optimal temperatures (T_opt's) for corona poling were obtained for the largest second‐order NLO response. The electrooptic coefficient (γ₃₃) of a polyimide at a wavelength of 830 nm was up to 21 pm/V after corona poling under its T_opt, and the value remained at elevated temperatures (>90.6% was retained at 240 °C for >120 h). The thermal stability of the NLO polyimides was studied with UV spectrometry after poling of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2478–2486, 2002     

Second-order Nonlinear Optical Properties of a Series of Benzothiazole Derivatives

The second-order nonlinear optical (NLO) properties of a series of benzothiazole derivatives were studied by use of the ZINDO-SOS method.These chromophores are formed by a donor- π- bridge-acceptor system,based on a nitro group connected with benzothiazole as the acceptor and a hydroxyl-functional amino group as the donor.For the purpose of comparison,we also designed molecules in which nitrobenzene is an acceptor,The calculation results indicate that benzothiazole derivatives exhibit larger second-odrder polarizabilities than nitrobenzene derivatives.In order to clarify the origin of the NLO response of these chromophores,their electron properties were investigated as well.The benzothiazole derivatives are good candidates for application in electro-optical device due to their high optical nonlinearities,good thermal and photonic stability.     

Systematic study of the structure-property relationship of a series of ferrocenyl nonlinear optical chromophores

A series of novel nonlinear optical (NLO) chromophores 1-4 incorporating the ferrocenyl (Fc) group as an electron donor and 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF) derivatives as electron acceptors are presented. The use of a constant Fc donor and varied acceptors and bridges makes it possible to systematically determine the contribution of the conjugated bridge and the acceptor strength to chromophore nonlinear optical activity. The X-ray crystal structures of all four chromophores allow for the systematic investigation of the structure-property relationship for this class of molecules. For example, the crystal structures reveal that both cyclopentadienyl groups in the ferrocenyl donor contribute to the electron donating ability. The first-order hyperpolarizabilities beta of these chromophores, measured by hyper-Rayleigh scattering (HRS) relative to p-nitroaniline are reported. These beta values are compared to those calculated by density functional theory (DFT). The excellent agreement between the theoretical and experimental beta values demonstrates that a linear relation exists between the hyperpolarizability and the bond length alternation. An electrooptic coefficient, r(33), of approximately 25 pm/V at 1300 nm, for compound 4, incorporated into a polymer matrix, is competitive with organic chromophores. Moreover, this r(33) is more than 30 times larger than the previously reported value for an organometallic chromophore in a poled polymer matrix. This work not only underscores the potential for Fc donor moieties, which have been underutilized, but also demonstrates that experimental characterization and theoretical simulations are now congruent, viable methods for assessing potential performance of NLO materials.     

Influence of thiazole regioisomerism on second-order nonlinear optical chromophores

Two series of matched and mismatched donor–thiazole–acceptor chromophores have been synthesized to disclose the role that the orientation of the thiazole ring plays on their second-order nonlinear optical (NLO) properties. Whereas previous theoretical studies predict that the matched systems show markedly higher NLO responses, our experimental results do not parallel this trend, showing differences between regioisomers much lower than those predicted.     

高活性、高产率非线性偶氮化合物的合成及其线性、非线性光学性能

合成了一类高产率的基于偶氮的新型非线性活性化合物. 初步测定其薄膜的折射率可在1.55—1.64范围内任意调节, 薄膜的Tg在130 ℃ 以上, 其未经优化的非线性光学系数γ33为16 pm/V(1310 nm), 该材料在通讯波长窗口的光学损耗较小, 化合物的热分解温度在239 ℃ 以上.     

Thermal stability and structural characterization of organic/inorganic hybrid nonlinear optical material containing a two-dimensional chromophore

In this study, two nonlinear optic hybrid materials with different dimensional alkoxysilane dyes were prepared and characterized. One NLO silane (Cz2PhSO 2OH- TES), a two-dimensional structure based on carbazole, had a larger rotational volume than the other (DR19-TES). Second harmonic ( d 33) analysis verified there is an optimum heating process for the best poling efficiency. The maximum d 33 value of NLO hybrid film containing Cz2PhSO 2OH was obtained for 10.7 pm/V after precuring at 150 degrees C for 3 h and poling at 210 degrees C for 60 min. The solid-state (29)Si NMR spectrum shows that the main factor influencing poling efficiency and thermal stability was cross-linking degree of NLO silane, but not that of TMOS. In particular, the two-dimensional sol-gel system has a greater dynamic and temporary stability than the one-dimensional system due to Cz2PhSO 2OH-TES requiring a larger volume to rotate in the hybrid matrix after cross-linking.     

NLO properties of metallabenzene-based chromophores: a time-dependent density functional study

The static and dynamic first hyperpolarizabilities for a series of substituted metallabenzene-based nonlinear optical (NLO) chromophores were determined by time-dependent density functional theory (TDDFT). The electronic excitation contributions to the first hyperpolarizability are rationalized in terms of the two-level model. The effects on the hyperpolarizabilities of (a) the metal center (Os, Ir, Pt); (b) the ligand environment (PH3, CO, Cl); (c) various donor and acceptor substituents (NH2, OH, Me, H, Cl, Br, I, COOMe, COOH, CN, NO2); and (d) the length of pi-conjugation were studied. Our calculations predict that metallabenzenes have significant second-order NLO susceptibilities, ranging from = 1.0 x 10(-29) to 5.6 x 10(-28) esu and from mu = 3.0 x 10(-47) to 1.1 x 10(-44) esu, that can be tuned by changing the metal center and/or ligand environment.     

Investigation of dipole alignments by swelling in poled thin films of a side-group polymer using second harmonic generation

This paper deals with relations between solvent diffusion and changes in second harmonic generation (SHG) in a side-group polymer with nonlinear optical (NLO) chromophores. The SHG signal of poled polymer thin films was measured as a function of time during the swelling process with methanol. The results indicated that the diffusion process was Fickian. The topographic results obtained by atomic force microscopy, together with the SHG data, also demonstrated the existence of the domain layer formed during poling that gave rise to the principal SHG intensity for this sample. Also, a noncentrosymmetric chromophore ordering was induced by swelling in the absence of a poling electric field. This time-varying SHG signal upon swelling was discussed in terms of dipolar and polar alignments of the side-group NLO chromophores. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3108–3114, 1999     

A relaxation study of poled nonlinear optical polymers by infrared reflection-absorption spectroscopy

The relaxation of poled nonlinear optical (NLO) chromophores in polymer films was characterized by infrared (i.r.) reflection-absorption spectroscopy. Both a guest-host system and a photocrosslinkable polymer system were investigated. Polymethylmethacrylate doped with either 2-methyl-4-nitroaniline or 4(4′-nitrophenylazo)aniline was studied. The photocrosslinkable polymer system, polyvinylcinnamate doped with 3-cinnamoyloxy-4-[4-(N,N-diethylamino)-2-cinnamoyloxy phenyl azo]nitrobenzene was also investigated. Doped NLO active molecules were aligned using the corona poling technique. i.r. spectra as a function of time were used to monitor the relaxation behavior of the oriented dyes after poling. Relaxation of NLO molecules was followed at various characteristic vibrational frequencies. The relaxation behavior of both systems were found to be consistent with those studied by the second harmonic generation technique.