New polyurethanes and polyesters for second‐order nonlinear optical applications

New polymers for second‐order nonlinear optical (NLO) applications were synthesized and characterized. They were distinguished by the presence of chromophore groups, with various molecular hyperpolarizability values, used as pendants on substantially rigid backbones. The polymers were prepared through the reaction of tolylene‐2,4‐diisocyanate, or a suitable alkyloxyphthaloyl dichloride, with the N,N‐diethanol‐4‐(phenyl) group azo‐linked to a nitrofluorenone, nitrostilbene, nitrooxadiazole, or nitrothiadiazole moiety. The polymers exhibited good thermal stability, high glass‐transition temperatures, and an absence of crystallinity. The second‐order NLO properties of thin, transparent poled films, prepared by spin coating and thermal corona poling, were investigated for some of the polymers. The second harmonic coefficients, ranging between 18 and 25 pm/V, depended more on the alignment of the chromophore groups along the direction of the poling field than on their molecular hyperpolarizability. The temporal stability of the NLO properties of the polymers was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3013–3022, 2004     

Synthesis and second‐order nonlinear optical properties of multifunctional polysiloxanes with sulfonyl‐based chromophores

Two new polysiloxanes ( P1 and P2 ) with a high density of sulfonyl‐based chromophores were prepared by a new two‐step method. Poly[methyl‐3‐(9‐carbazolyl)propyl siloxane] was partially formulated by the standard Vilsmeier reaction, and formyl groups of high reactivity were condensed with cyanoacetylated chromophores; this yielded polysiloxanes P1 and P2 in almost complete conversions. Their structures were verified with ¹H NMR, IR, and ultraviolet–visible spectra. P1 and P2 exhibited good solubility in common organic solvents and were thermally stable. The maximum absorptions appeared at about 452 and 390 nm for P1 and P2 , respectively, in tetrahydrofuran; they were blueshifted about 42 and 8 nm, respectively, in comparison with those of the corresponding chromophores with a nitro acceptor and resulted in a wider transparency window. The P1 values of the nonlinear optical coefficient (d₃₃), measured by in situ second harmonic generation, was 16.2 pm/V. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1317–1324, 2005     

Synthesis and characterization of Y‐type polymers for second‐order nonlinear optical applications

A series of dicyanomethylene‐substituted polymers having Y‐type molecular architecture were synthesized by Knoevenagel condensation reaction. The polymers were found to be soluble in organic solvents like tetrahydrofuran and chloroform. From gel permeation chromatography, the molecular weights of the polymers were found to be in the range of 15,300–33,800 g/mol. Thermal analysis showed that the polymers were stable up to 350 °C with glass transition temperature (T_g) in the range of 129–212 °C. These polymers were found to form good optical quality films. The order parameter was calculated to be in the range of 0.01–0.48. Atomic force microscopy indicated prominent morphology changes due to alignment of dipoles after poling. By using Nd:YAG laser of 1064 nm, angular dependence and temperature dependence of second‐harmonic generation intensity were investigated. The geometry optimization, shape of polymers, and restricted torsion angle between acceptor and donor substituents (push–pull system) were calculated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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     

Synthesis and characterization of photocrosslinkable,side‐chain,second‐order nonlinear optical poly(ester imide)s with great film‐forming ability and long‐term dipole orientation stability

A series of photocrosslinkable, side‐chain, second‐order nonlinear optical (NLO) poly(ester imide)s (PEIs) based on a chromophore‐containing dianhydride, 2,2′‐{4‐[(4‐nitrophenyl)‐azo]phenyl}iminobis(ethyl benzene‐1,2‐dicarboxylic acid anhydride‐4‐carboxylate), benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride, and 4,4′‐diamino‐3,3′‐dimethyl diphenylmethane were prepared. The resulting PEIs exhibited many useful physical characteristics, such as good organosolubility, excellent film‐forming properties, high glass‐transition temperatures (186–229 °C), and high thermal decomposition temperatures. The electrooptic coefficient value of PEI3 at 650 nm was 11.5 pm/V, and high long‐term stability of the NLO chromophore alignment in the poled PEI3 film at 120 °C was observed. The temporal stability of the dipole orientation at 150 °C was further enhanced by ultraviolet irradiation because of photocrosslinking. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 303–312, 2003     

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.     

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 nonlinear optical properties of copolymers of fluoro-containing bisphenol A and chromophores

A series of new fluoro-containing copolymers have been synthesized by a Mitsunobu reaction with 4,4’-（hexafluoroisopropylidene） bisphenol A（6FBPA） and the corresponding N,N-dihydroxyethylaminoaryl azo or ring-locked triene compounds, which have high thermal stability and good solubility in organic solvents.The nonlinear optical（NLO） measurements made by Marker fringe method at 1064 nm indicate that the copolymers embedded with the ring-locked triene and azo chromophores exhibit higher macroscopic nonlinear optical coefficient（70.2 pm/V and 26.5-34.6 pm/V,respectively）.Thermal analysis and UV-visible absorption spectra show that the copolymers have good thermal stability（T_d= 264-319℃） and optical transparency (λ_max<500 nm).     

Synthesis and nonlinear optical properties of hyperbranched polytriazole containing second‐order nonlinear optical chromophore

The hyperbranched polytriazole (hb‐PTA) containing second‐order nonlinear optical chromophore was synthesized through “A₂ + B₃” approach based on “click reaction.” Its corresponding linear analogue (l‐PTA) was prepared for comparison. The hb‐PTA has better solubility in common organic solvents than the l‐PTA. Both the polymers exhibit good thermal stability with 5% weight loss temperatures over 260 °C. The poled film of hb‐PTA exhibits much higher second‐harmonic coefficient (96.8 pm/V) than that of l‐PTA (23.5 pm/V). The three‐dimensional spatial isolation effect resulting from the highly branched structure and the crosslinking of the terminal acetylene groups at moderate temperature play important roles in the enhancement of optical nonlinearity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1140–1148, 2008     

Synthesis and properties of nonlinear optical side chain soluble polyimides for photonics applications

Aromatic polyimides with side chain nonlinear optical chromophores have been investigated through a facile two-step synthetic route. First, various poly(hydroxy imide)s have been synthesized by direct thermal imidization of diaminophenol dihydrochloride salt and aromatic dianhydride monomers. The resulting polyimides bearing phenolic hydroxy groups were found to react easily with the terminal hydroxy group on the chromophores via the Mitsunobu condensation to give corresponding polyimides with high optical nonlinearities and good solubility in common organic solvents. Detailed physical properties showed that these polyimides have a molecular weight (M_w) of 31,000 and high glass transition temperature above 220°C, ensuring a long-term alignment stability at elevated temperature. The electrooptic coefficients, r₃₃, of the electrically poled polymer films were in the range 1.8–7.6 pm/V at 1.3 μm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 301–307, 1998     

Dendronized tricyanopyrroline‐based chromophores in nonlinear optical active host polymer

We synthesized new nonlinear optical (NLO) chromophores containing a 3,5‐bis(3,5‐bisbenzyloxy‐benzyloxy)‐benzoate dendron. Tricyanopyrroline (TCP)‐based chromophores were designed and prepared by virtue of its strong electron withdrawing property. A soluble polyimide containing 6‐({4‐[2‐(1‐allyl‐4‐cyano‐5‐dicyanomethylene‐2‐oxo‐2,5‐dihydro‐1H‐pyrrol‐3‐yl)‐vinyl]‐phenyl}‐butyl‐amino)‐hexanoyl group in the side chain was also prepared as an NLO active host polymer. A benzoate dendron was tethered at two different binding positions of the chromophore to yield two different guest molecules. Thin‐film composites of these dendronized chromophores dissolved in the NLO active polyimide host were employed to fabricate the electro‐optic (EO) samples. The EO properties of new NLO polyimides containing dendronized chromophores were compared with those of the sample with nondendronized plain chromophores. The effect of a bulky dendron on the EO properties was investigated using an in situ reflection technique. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5064–5076, 2008     

Poly(4‐vinylpyridine) as the host ligand of metal‐containing chromophores for second‐order nonlinear optical active materials

Two formulas of grafted polymers with metal‐containing chromophores, potentially suitable for second‐order nonlinear optics applications, are described. Two chromophores were obtained from a tridentate ligand coordinated to Cu(II) or Pd(II) ions. The organometallic chromophore fragments were grafted to poly(4‐vinylpyridine) by the pyridinic nitrogen of the host polymer. Some qualities displayed by the new metallated polymers are remarkable: (1) a high value of the first hyperpolarizability coefficient of the chromophores, (2) a high content of the grafted chromophore in the polymers (up to 60 wt %), (3) a considerable increase in the glass‐transition temperatures (up to 240 °C), (4) good thermal stability in air (ca. 280 °C), and (5) good optical transparency of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2987–2993, 2002     

New perylene polyimides containing p‐n diblocks for sensitization in TiO2 solar cells

Three novel perylene polyimides (PPIs) containing p‐n diblock units were designed and synthesized for use in dye‐sensitized mesoporous TiO₂ solar cells. They all dissolve in m‐cresol and N‐methyl‐2‐pyrrolidone (NMP). Their visible light absorption, electrochemical and photoelectrochemical properties were systematically studied. The polyimides have band gap energies of 2.16, 2.19 and 2.25 eV deduced from ultraviolet–visible absorption spectra, and electron affinity (E_a) and ionization potential (IP) of ?3.93 and 6.10 eV for PPI1, ?3.94 and 6.13 eV for PPI2, ?3.93 and 6.59 eV for PPI3, respectively, deduced from cyclic voltammogram. Experimental data show that introduction of 4,4′‐bisaminetriphenylamine cannot only greatly enhance optic‐electro conversion efficiency, but also enhance the dissolubility which in favorable for making the devices. The relationship of structure and properties of PPI is discussed and the mechanism of photocurrent generation is explained. Copyright © 2004 John Wiley & Sons, Ltd.     

Click chemistry‐based synthesis of azo polymers for second‐order nonlinear optics

Four linear polymers containing pendant azo moiety were synthesized through click chemistry for second‐order nonlinear optical study. The polymers were found soluble in most of the polar organic solvents such as tetrahydrofuran (THF), chloroform, and dimethyl formamide (DMF). The polymers showed thermal stability up to 300 °C and glass transition temperatures (T_g) in the range of 120–140 °C. The molecular weights (M_w) of these polymers (measured by gel permeation chromatography) were in the range 37,900–55,000 g/mol. The polymers were found to form optically transparent films by solution casting from THF solution. Order parameters were calculated from UV–vis absorption spectra. The morphology changes in the films after poling were characterized by atomic force microscopy. The angular dependence, temperature dependence, and time dependence of second harmonic generation (SHG) intensity were obtained by using 1064 nm Nd:YAG laser. The SHG intensity remained unchanged up to 95 °C. At room temperature, it remained stable up to 8 days after initial drop of about 14%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular design,synthesis, and nonlinear optical properties of novel T‐type polyimides with exceptionally high thermal stability of the second harmonic generation

2,5‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐4′‐nitrostilbene dianhydride was prepared and reacted with 1,4‐phenylenediamine, 4,4′‐oxydianiline, 4,4′‐diaminobenzanilide, and 4,4′‐(hexafluoroisopropylidene)dianiline to yield unprecedented novel T‐type polyimides ( 4 – 7 ) containing 2,5‐dioxynitrostilbenyl groups as nonlinear optical chromophores, which constituted parts of the polymer backbones. 4 – 7 were soluble in polar solvents such as acetone and N,N‐dimethylformamide. They showed thermal stability up to 300 °C in thermogravimetric analysis thermograms; the glass‐transition temperatures obtained from differential scanning calorimetry thermograms were around 153 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064‐cm^?1 fundamental wavelength were around 4.35 × 10^?9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 45 °C higher than the glass‐transition temperature, and there was no SHG decay below 200 °C because of the partial main‐chain character of the polymer structure, which was acceptable for nonlinear optical device applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3189–3199, 2004     

Donor–acceptor diethynylsilane oligomers: A second‐order nonlinear optical material

The interest in the study of oligomers has been motivated mainly because of their solubility in common solvents and also their capacity to be crystallized, which allowed for chemical processing leading to important applications in the area of material sciences. In this work, we carried out an investigation of polydiethynylsilane (PDES) decamers substituted with electron donor (D) and acceptor (A) groups, which is certainly of relevance, once PDES itself is known to display large third‐order optical susceptibility. Therefore, density functional theory calculations of static first hyperpolarizability (β) were performed using various functionals with the 6‐31G(d) basis set along with correlated MP2 calculation used as reference for comparison. The influence of A and D substituents on the magnitude of β was investigated by matching the acceptor (dicyanovinyl, nitrobenzene) and donor (propyl, propoxy, and phenylamine) groups attached at both ends of the oligomer. The largest β value was predicted for the derivative having the phenylamine and dicyanovinyl groups, which is around 30 times the relative value for the nonsubstituted decamer, what is a very impressive enhancement reported for the first time in the literature, strongly suggesting that disubstituted diethynylsilane decamers are potential building blocks for molecular‐based materials with second‐order nonlinear responses. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1410–1419, 2011     

Design and synthesis of a thermally stable second‐order nonlinear optical chromophore and its poled polymers

A multiple charge‐transfer second‐order nonlinear optical (NLO) chromophore 2,3‐bis(4‐aminophenyl)‐5,6‐dicyanopyrazine (BAPDCP) was successfully designed and synthesized. It was characterized by ¹H NMR, mass spectrometry, Fourier transform infrared spectroscopy, and elemental analysis. The first hyperpolarizability β of BAPDCP was measured with the Hyper–Rayleigh scattering technique, which was 123.5 × 10^?30 esu. The donor‐embedded prepolyimide and prepolyurea were also synthesized by a polyaddition reaction. Thermogravimetric analysis and differential scanning calorimetry demonstrated that either the chromophore or the polymers have fine thermal stability. The thin films of prepolymers were prepared by coating on ITO glass substrate and poled by corona poling at elevating temperature. The second‐order NLO coefficients d₃₃ of the films were measured by in situ second‐harmonic generation measurements. The d₃₃ were deduced as 27.7 and 16.5 pm/V for polyurea and polyimide at 1064 nm fundamental wavelength, respectively. The onset depoling temperature of the polyimide and polyurea were both as high as 200 °C. To understand the temperature effect to the orientation thermal stability of polyimide, two films were treated at different final poling temperatures. The depoling experimental results showed that the orientation stability is higher, as raising the final treated temperature but the d₃₃ value are almost similar. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2846–2853, 2003     

Theoretical study on the second‐order nonlinear optical properties of nonconjugated D‐π‐A chromophores

Density functional theory calculations have been carried out on nonconjugated D‐π‐A chromophores to investigate the different electron donors and conjugated bridges effects on the molecular nonlinear optical response. The results show that the large second‐order polarizability values can be achieved through careful combination of available electron donors, conjugated bridges for our studied nonconjugated D‐π‐A chromophores. The calculations also provide a clear explanation for the second‐order polarizability changes from the standpoint of transition energies, oscillator strengths, electron density difference, and bond length alternation. Solvent effect has great influence on the second‐order polarizability and electronic absorption spectrum. It is hoped that the results presented in this article will give some hints to the interrelated studies. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

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     

A facile approach to prepare soluble side‐chain polyimides for second‐order nonlinear optics

A simple and generally applicable new synthetic method to prepare second‐order nonlinear optical (NLO) polyimides has been developed. In this approach, side‐chain‐substituted polyimides were synthesized via isocyanato‐terminated prepolymers prepared directly from NLO chromophore‐containing diols Disperse Red 19. Using this technique, the tedious synthesis of the classical diamine monomers and harsh imidization process associated with polyamic acid prepolymers are avoided. The resulting polymers possessed good solubility and high glass‐transition (171–211 °C) and thermal‐decomposition temperatures. The polymers also exhibited excellent film‐forming properties, and good optical‐quality films were easily obtained by spin coating. The second‐order NLO activities of the polymer films were also studied, and several factors that might determine the growth of the second‐order NLO activity were proposed. The polymers obtained exhibit a large second‐order NLO activity (34–52.5 pm/V at 1064 nm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2189–2195, 2001