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.     

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 %     

SYNTHESIS AND CHARACTERIZATION OF NOVEL SOL-GEL DOPED ORGANIC／INORGANIC HYBRID NONLINEAR OPTICAL MATERIALS

4-hydroxy-4 ‘-nitro azobenzene (NHA) and 4-amino-4 ‘-nitro azobenzene (DO3) were prepared respectively from p-nitrophenylamine as a precursor compound. Two kinds of doped organic/inorganic hybrid nonlinear optical (NLO) materials containing NHA and DO3 were synthesized by Sol-Gel process. The preparation and properties of two NLO materials were studied and characterized by FTIR, IH-NMR, UV-VIS, SEM, DSC and SHG measurements. The results show that the maximum doping amounts of NHA and DO3 in two doped hybrid NLO materials are 7.2(wt)% and ll.3(wt)% respectively, and the corresponding second-order NLO coefficients (d33values) are 2.91 ×l0^-3esu and 6.14×10 -8 esu. Two doped NLO materials have relatively good RT stability, after 90 days at RT the d33 values can maintain about 85% of their initial values, but after l0h at 100℃ can only maintain about 50% of their initial values. In this report, the reasons for high-temperature instability of doped materials were discussed, and the possible improvements were also suggested.     

Low loss second‐order non‐linear optical crosslinked polymers based on a phosphorus‐containing maleimide

A series of crossslinked organic and organic/inorganic polymers based on maleimide chemistry have been investigated for second‐order non‐linear optical (NLO) materials with excellent thermal stability and low optical loss. Two reactive chromophores (maleimide‐containing azobenzene dye and alkoxysilane‐containing azobenzene dye) were incorporated into a phosphorus‐containing maleimide polymer, respectively. The selection of the phosphorus‐containing maleimide polymer as the polymeric matrices provides enhanced solubility and thermal stability, and excellent optical quality. Moreover, a full interpenetrating network (IPN) was formed through simultaneous addition reaction of the phosphorus‐containing maleimide, and sol‐gel process of alkoxysilane dye (ASD). Atomic force microscopy (AFM) results indicate that the inorganic networks are distributed uniformly throughout the polymer matrices on a nano‐scale. The silica particle sizes are well under 100 nm. Using in situ contact poling, the r₃₃ coefficients of 2.2–17.0 pm/V have been obtained for the optically clear phosphorus‐containing NLO materials. Excellent temporal stability (100°C) and low optical loss (0.99–1.71 dB/cm; 830 nm) were also obtained for these phosphorus‐containing materials. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis and nonlinear optical properties of novel Y‐type polyester containing tricyanovinylthiazolylazoresorcinoxy group with enhanced thermal stability of dipole alignment

Novel Y‐type polyester 4 containing 5‐methyl‐4‐{5‐(1,2,2‐tricyanovinyl)‐2‐thiazolylazo}resorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer backbone, was prepared, and its NLO properties were investigated. Polyester 4 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. Polymer 4 shows a thermal stability up to 250 °C from thermogravimetric analysis with glass‐transition temperature obtained from differential scanning calorimetry of approximately 94 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1560‐nm fundamental wavelength is 8.12 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 6 °C higher than glass‐transition temperature (T_g), and no significant SHG decay is observed below 100 °C due to the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and electro‐optic properties of novel X‐type polyurethane containing nitrophenylazonitroresorcinoxy group with highly enhanced thermal stability of dipole alignment

Novel X‐type polyurethane 4 containing 4‐(4‐nitrophenylazo)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer main chains, was prepared and characterized. Polyurethane 4 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stabilities up to 270 °C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry of about 134 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064 nm fundamental wavelength is 5.37 × 10^?9 esu. Polymer 4 exhibits a thermal stability up to T_g, and no significant SHG decay is observed below 135 °C, which is acceptable for NLO device applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 760–766     

The design,synthesis, and nonlinear optical properties of novel X‐type polyurethane containing dicyanovinylnitroresorcinoxy group with enhanced SHG thermal stability

Novel X‐type polyurethane 5 containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature (T_g) obtained from differential scanning calorimetry thermogram of around 120 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064‐nm fundamental wavelength is around 6.12 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 5 °C higher than T_g, and there was no SHG decay below 125 °C due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

POLYIMIDE/INORGANIC INTERPENETRATING POLYMER NETWORKS FOR STABLE SECOND-ORDER NONLINEAR OPTICS

Thermally stable NLO interpenetrating polymer networks (IPNs) based on an organosoluble polyimides functionalized with methacryloyl groups (PIB), and an alkoxysilane dye (ASD) have been developed. IPNs were formed through the free radical polymerization of methacryloyl group containing PIB, and sol-gel process of ASD. Optically clear samples exhibit large second-order optical nonlinearity (d₃₃ = 6.9-39.6 pm/V at 1064 nm) after poling and curing at 180°C for 2 hours. The temporal stability of the PIB/ASD IPN samples was much better than the inter-chain crosslinking polyimide/inorganic samples. The high rigidity of the polymer backbone and the interpenetrating structure of the polymer networks prevent the randomization of the aligned NLO chromophores     

Molecular design,synthesis, and properties of Y‐type nonlinear optical polyester containing tricyanovinylthiophene with enhanced thermal stability of second harmonic generation

1‐{3,4‐Di‐(2‐hydroxyethoxy)phenyl}‐2‐(2‐thiophenyl)ethene (5) was prepared and condensed with terephthaloyl chloride to yield polyester (6). Polymer 6 was reacted with tetracyanoethylene to give a new Y‐type polyester (7) containing 1‐(3,4‐dioxyethoxy)phenyl‐2‐{5‐(2,2,3‐tricyanovinyl)‐2‐thiophenyl)}ethenyl groups as NLO‐chromophores, which are components of the polymer backbones. Polyester 7 is soluble in common organic solvents such as N,N‐dimethylformamide and acetone. Polymer 7 showed a thermal stability up to 300 °C in thermogravimetric analysis with glass transition temperature (T_g) obtained from differential scanning calorimetry near 126 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at the 1560 nm fundamental wavelength was around 6.57 × 10^?9 esu. The dipole alignment exhibited high thermal stability up to the T_g, and there was no SHG decay below 125 °C due to the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1911–1919, 2009     

Synthesis and properties of novel Y‐type nonlinear optical polyimides with high thermal stability of second harmonic generation

2,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐1‐(2,2‐dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 4,4′‐oxydianiline, 4,4′‐diaminobenzanilide and 4,4′‐(hexafluoroisopropylidene)dianiline to yield novel Y‐type polyimides 5‐7 containing 2,4‐dioxybenzylidenemalononitrile groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5‐7 are soluble in polar solvents such as dimethylsulfoxide and N,N‐dimethylformamide. Polymers 5‐7 showed a thermal stability up to 330 °C in thermogravimetric analysis thermograms with T_g values obtained from differential scanning calorimetry thermograms in the range 179–194 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength were around 5.56 × 10^?9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 20 °C higher than the glass‐transition temperature there was no SHG decay below 215 °C because of the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3078–3087, 2008     

Synthesis and characterization of NLO chromophores bearing poly(1,6-heptadiyne)s for electro-optic application

We utilized the metathesis reaction to synthesize a new type of multifunctional polymer that contains a conjugated backbone and a second-order NLO chromophore as a pendant group. The 1,6-heptadiyne derivatives bearing NLO chromophores were easily polymerized by using a metathesis catalyst to give corresponding polymers with large optical nonlinearities. Molecular structural characterizations for the resulting polymers were achieved by ¹H- and ¹³C-NMR, FTIR, and UV-visible spectroscopies. Soluble polymers were obtained up to 72 mol % of chromophore monomer portion in the copolymer. These amorphous polymers exhibited good film-forming abilities and thermal stability. The electro-optic coefficient, r₃₃, of the poled polymer films was in the range of 0.5–10.1 pm/V, and the nonresonant values of the third-order NLO coefficient, χ⁽³⁾ was found to be about 10⁻¹¹ esu. © 1996 John Wiley & Sons, Inc.     

Synthesis of nonlinear optical maleimide copolymer by polymer reaction and their electro-optic properties

Thermally stable poly(α-methyl styrene-co-maleimide) (MSMI) and poly(α-methyl styrene-co-4-carboxyphenyl maleimide) (MSCM) substrate polymers were obtained readily by free radical polymerization of comonomers. Introduction of a DR1 chromophore to the maleimide units of MSMI substrate polymer by the Mitsunobu reaction was dependent on the reaction solvent. The degree of substitution of DR1 into the MSMI polymer was bound to be 91.1 mol % and 0.4 mol % by UV spectrometers in the THF and DMF solvent, respectively. DR1 chromophore was, however, substituted in the MSCM polymer at 33.0 mol % by Mitsunobu reaction in the THF solvent. Both substrate and NLO polymer exhibited high thermal stability due to the incorporation of maleimide units in the polymer chain. The glass transition temperature (T_g) and initial decomposition temperature (T_i) of the NLO polymer were in the range of T_g = 185°C and T_i = 310–345°C. The electro-optic coefficient (r₃₃) of NLO polymer was determined with an experimental setup capable of the real-time measurement while varying both the poling field and temperature. The NLO polymer MSMI-THF had a higher r₃₃ value than MSCM-DR due to an increased degree of substitution of DR1 chromophore. MSMI-THF had a maximum r₃₃ value of 16 pm/V at 135 MV/m poling field with a 632.8 nm light source. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3715–3722, 1999     

Synthesis and nonlinear optical properties of novel Y‐type polyurethane containing tricyanovinylthiazole with enhanced thermal stability of second harmonic generation

A novel Y‐type poly[iminocarbonyloxyethyl‐5‐methyl‐4‐{2‐thiazolylazo‐4‐(1,2,2‐tricyanovinyl)}resorcinoxyethyloxycarbonylimino‐(3,3′‐dimethoxy‐4,4′‐biphenylene)] 4 containing 5‐methyl‐4‐{5‐(1,2,2‐tricyanovinyl)‐2‐thiazolylazo}resorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 4 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It showed a thermal stability up to 250 °C in thermogravimetric analysis thermogram and the glass‐transition temperature (T_g) obtained from differential scanning calorimetry thermogram was around 118 °C. The second harmonic generation coefficient (d₃₃) of poled polymer films at 1560 nm fundamental wavelength was around 8.43 × 10^?9 esu. The dipole alignment exhibited a thermal stability even at 12 °C higher than T_g, and there was no SHG decay below 130 °C due to the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1166–1172, 2010     

SYNTHESIS OF A NOVEL SELF-ASSEMBLING NLO POLYMERIC FILM*

By covalently binding chromophore NPP, N-(4-nitrophenyl)-(L)-prolinol, to a structurallycontrolled cage-like cross-linking polymer (SCCP), a modified nonlinear optical (NLO) polymeric filmprepared by "in situ poling and sol-gel" process successfully overcame the fundamental problem of NPPchromophores subliming out from the cages of the "doped" NLO polymeric film when heated or placed underUV light. Its d_(33) (coefficient of second harmonic generation) is 2.0×10~(-8) esu. measured by IR dichroism. Themodified film has a low decay of the SHG signal and preserves 94% of the initial value after 50 days at roomtemperature. These properties match that of the "doped" film, indicating that the modified film also retainsthe main advantages of the "doped" film.     

[C5H12N]SnCl3: A Tin Halide Organic–Inorganic Hybrid as an Above-Room-Temperature Solid-State Nonlinear Optical Switch

Nonlinear optical (NLO) switches driven by a solid-state structural phase transition have attracted extensive attention; however, above-room-temperature solid-state NLO switch materials are still sparse. Herein, we report an above-room-temperature tin halide organic–inorganic hybrid quadratic NLO switchable material, N-methylpyrrolidinium trichloride stannite ([C₅H₁₂N]SnCl₃, MPSC). The MPSC crystal exhibits a phase-matchable NLO property that is 1.1 times that of KH₂PO₄ (KDP) and NLO switching behavior, changing from a high second harmonic generation (SHG) response to a low SHG response at 383 K, thereby demonstrating its prospective applications in the field of nonlinear optics. Variable-temperature crystal structural analysis combined with theoretical calculations revealed that the large NLO response stems from the inorganic SnCl₃ moiety, whereas the high-performance NLO switching properties mainly originate from the order/disorder transformation of the N-methylpyrrolidinium. This work provides a new approach to designing and exploring new high-performance quadratic NLO switches involving tin halide organic–inorganic hybrids.     

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.     

Stable second‐order nonlinear optical poly(amide–imide)/inorganic materials via simultaneous sequential self‐repetitive reaction and sol–gel process

A series of thermally stable organic/inorganic second‐order nonlinear optical (NLO) composites via sequential self‐repetitive reaction (SSRR) and sol–gel process has been developed. This SSRR is based on carbodiimide (CDI) chemistry. The difunctional azo chromophores (2,4‐diamino‐4′‐(4‐ nitrophenyl‐diazenyl)azobenzene (DNDA)) was reacted with excessive amount of 4, 4′‐methylene‐ diphenylisocyanate (MDI) to form poly‐CDI, and subsequently trimellitic anhydride (TMA) was added to obtain poly(N‐acylurea). The organic/inorganic composites containing prepolymer of phenyltriethoxysilane (PTEOS) and poly(N‐acylurea) in different weight ratios (10:90, 30:70, 50:50, 70:30, 90:10 wt%) were prepared, respectively. The moderate glass transition temperature (T_g) characteristic of the poly(N‐acylurea) allows the NLO‐active polymer to achieve high poling efficiency. After in situ poling and curing process, the T_gs of the composites were elevated, and higher than that of the pristine poly(amide–imide) sample. Electro‐optical (EO) coefficients (r₃₃) of about 5.5 ～ 18.0 pm/V at 830 nm were obtained. Excellent temporal stability at 100°C, and waveguide characteristics (3.1–4.2 dB/cm at 830 nm) were also obtained for these composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular design, synthesis and electro-optic properties of novel Y-type polyurethanes with high thermal stability of second harmonic generation

2,4-Di-2^′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3^′-dimethoxy-4,4^′-biphenylenediisocyanate to yield unprecedented novel Y-type polyurethanes (4-5) containing 2,4-dioxybenzylidenemalononitrile group as a nonlinear optical (NLO) chromophore, which constitutes a part of the polymer backbone. The resulting polyurethanes 4-5 were soluble in common organic solvents such as acetone and DMF. Polymers 4-5 showed a thermal stability up to 260 °C from thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) giving T_g values around 143-156 °C. The approximate lengths of aligned NLO-chromophores estimated from AFM images of poled polymer films were about 10 nm. The SHG coefficients (d₃₃) of poled polymer films were around 7.4 × 10⁻⁹ esu. These Poled polymers exhibited a greater thermal stability of dipole alignment even at 10 °C higher than T_g, and no SHG decay was observed below 155 °C due to the partial main chain character of the polymer structure and extensive hydrogen bonds between urethane linkage, which is acceptable for NLO device applications.     

Electro-optical properties and nonlinear response of side chain liquid crystalline polymers

Among the NLO processes that have been studied, one of the most visually dramatic is the frequency doubling. In the field of optical information storage this process can provide the conversion of near-infrared laser light from diode lasers into deep blue light. Compared to the more traditional inorganic NLO materials, polymers with polarizable aromatic pendant side groups are increasingly being recognized as the materials of the future. Recently it has been pointed out that the axial ordering spontaneously present in nematic and smectic A polymers can be used to enhance field-induced polar ordering by elongating the orientational distribution function along the electric field direction. Depending on the value of the microscopic order parameters <P>₂ and <P>₄, the performance may be improved by a factor of 1 to 5 by using LCPs instead of ordinary amorphous polymers for SHG.^1-4) Interesting results have been obtained for copolyethers prepared by chemical modification of polyepichlorohydrin with classical 4-cyano-4'-hydroxybiphenyl mesogenic group which possesses NLO properties itself.^5-8) These copolyethers afford the opportunity to fine-tune the polymer properties by varying the concentration of the mesogenic side groups. As the concentration is increased, we move from a purely isotropic polymer to a nematic polymer. Spin-coated films have been activated using the corona poling technique and the order parameters <P>₂ have been determined from optical absorption spectra. The second harmonic coefficients d₃₃ and d₃₁ have been measured and compared with different statistical models. In view of the great practical importance, characterization of the wavelength dispersion has been carried out. It agrees well with the two-level approximation model. The dynamics of optical SHG has been investigated. It has been shown that both the presence of LC character in the material and the temperature at which the films are stored below Tg are important in determining the stability of the SH coefficients. A polyacrylate and a polymethacrylate bearing the same 4-cyanobiphenyl-based side groups have also been studied.^7-8) Of particular interest is the fact that the former is nematic while the latter is purely isotropic at rest, the addition of a methyl group to each structural unit of the polyacrylate backbone creating a higher conformational barrier to mesogen packing. Studies of the temporal and thermal characteristics of the poling process have been performed to: •understand and control the poling process with the intention of maximizing poling induced nonlinearity and stability. •elucidate the influence of the polymer backbone, our data including the use of the same mesogenic unit attached to increasing flexible backbones (e.g. polymethacrylate and polyether). •establish if, in the isotropic cases, noticeable axial order can be induced by the poling field, especially when the system is pulled through nematic/isotropic transition by the electric field.     

Nonlinear optical polyimides consisting of chromophore‐containing dendrons with site‐isolation effect

To investigate the dendritic structure effects on the electro‐optical (EO) coefficients and thermal stability of the nonlinear optical (NLO) active materials, a bifunctional compound, IDD (4‐isocyanato‐4′(3,3‐dimethyl‐ 2,4‐dioxo‐acetidino)‐diphenylmethane) was used as a building block to synthesize a series of novel NLO chromophore‐containing dendritic structures including Generation 0.5 (G0.5) to Generation 3 (G3). The glass transition temperatures (T_g) of G1–G3 dendrons were in the range of 76–116°C, whereas only the G0.5 dendron exhibited a melting temperature (T_m), 98°C. Moreover, a series of NLO‐active guest–host systems ranging from polyimide‐G0.5 (PI‐G0.5) to polyimide‐G3 (PI‐G3) were prepared by blending 20 wt% chromophore‐containing dendron with a high T_g polyimide. EO coefficients ranged from 6.1 to 12.9 pm/V. The r₃₃/dye content ratio increased with increasing generation of dendron‐containing polyimide samples. Particularly, the improvement in r₃₃/dye content ratio of PI‐G2.5 sample tripled as compared to that of the guest–host sample with Disperse Red 1. Excellent temporal stability of PI‐G0.5 and PI‐G1.5 at 80°C was obtained. Moreover, waveguide properties for NLO polymers containing higher generation dendrons (3.1–3.6 dB/cm at 830 nm) were also obtained. Copyright © 2008 John Wiley & Sons, Ltd.