Second-order nonlinear optical (NLO) polymers containing perfluoroaromatic rings as isolation groups with Ar/Ar self-assembly effect: Enhanced NLO coefficient and stability

Four new polyaryleneethynylenes P1–P4, which contained different aromatic or perfluoroaromatic isolation groups, were successfully prepared, via the palladium-catalyzed Sonogashira coupling reaction. Among them, P2, due to the presence of the self-assembly effect between the perfluoroaromatic and chromophore moieties, demonstrated much larger NLO effect (d₃₃ value of 162.3 pm/V) and better stability with onset temperature for decay (111 °C). The research on the polymer conformation suggested that perfluorophenyl groups in different positions would result in different effects on the NLO coefficient, providing some useful information for the design of NLO polymers with better performance.     

New hyperbranched polymers containing second-order nonlinear optical chromophores: Synthesis and nonlinear optical characterization

Three hyperbranched polymers (P1-P3) containing second-order nonlinear optical chromophores were synthesized by copolymerization of aromatic dialdehydes (carbazole, triphenylamine or benzene moieties) with sulfonyl-based chromophores attached with three active methylene groups, from “A₂ + B₃” approach based on simple Knoevenagel reaction. For comparison, their corresponding linear analogue polymers (P4-P6) were prepared. All the polymers are soluble in common organic solvents, and exhibit good thermal stability. The tested NLO properties of the hyperbranched polymers are better than their corresponding linear polymers, due to the three-dimensional spatial separation of the chromophores in the obtained hyperbranched polymeric structures.     

Synthesis of novel poly{methyl-[3-(9-indolyl)propyl]siloxane}-based nonlinear optical polymers via postfunctionalization

A novel series of nonlinear optical (NLO) polysiloxanes with a high density of chromophore moieties based on poly{methyl-[3-(9-indolyl)propyl]siloxane} (PMIPS) were synthesized by a post functional strategy. First, PMIPS (P1) was prepared through hydrosilylation reaction, then P1 is partially formylated by the reaction between P1 and the reagents of dimethylformamide (DMF) and phosphorus oxychloride under the standard Vilsmeier reaction conditions, and these formyl groups with high reactivity are condensed with four predesigned cyanoacetylated chromophores to afford the series of chromophore functionalized polysiloxanes (P3-6). The most special point is the molar concentrations of chromophore moieties are the same in polymers P3-6, which makes it convenient to study the behavior of different chromophores in the polymeric system. The poled films of P3-6 reveal the resonant d₃₃ values in the range of 7.9-55.2 pm/V by second harmonic generation (SHG) measurements.     

Novel second-order nonlinear optical main-chain polyurethanes: Adjustable subtle structure, improved thermal stability and enhanced nonlinear optical property

A series of main-chain polyurethanes containing sulfonyl-based NLO chromophores in the polymer backbone were prepared, the subtle structure of the chromophore moieties could be easily modified to adjust the property of the resultant polymers. The polymers exhibit improved stability of their enhanced NLO effects, besides their good processability, thermal stability, and relatively good transparency. 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 β value to possibly higher macroscopic NLO property efficiently, and BOP moieties are the best choice for this series of polymers to achieve optimized properties.     

Synthesis and characterization of polysiloxanes containing carbazolyl and sulfonyl-indole based chromophore as side chains

A new post-functional strategy was developed to prepare polysiloxanes with the sulfonyl-indole based chromophore and carbazolyl side groups. Thus a polysiloxane (P1) with indole and carbazolyl groups as side chains was first synthesized through hydrosilylation reaction, and then the post-azo coupling of p-ethylsulfonylbenzenediazonium fluoroborate toward the indole rings afforded the multifunctional sulfonyl-indole based chromophore-functionalized polysiloxane (P2 and P3). The polymers were easily soluble in common organic solvents, and their maximum absorption appeared at 394 nm, which is about 30 nm blue-shifted compared to the corresponding chromophore with nitro acceptors, and could result in a wider transparency window. The poled films of P2 and P3 reveals a resonant d₃₃ value of 12 and 18 pm/V, respectively, by second harmonic generation (SHG) measurements.     

Synthesis and nonlinear optical properties of soluble fluorinated polyimides containing hetarylazo chromophores with large hyperpolarizability

The novel fluorinated polyimides with side-chain nonlinear optical (NLO) chromophores were synthesized from hydroxyl polyimides, followed by the Mitsunobu reaction with NLO chromophores. Molecular structural characterization for the resulting polymers was achieved by ¹H NMR, FT-IR, UV-Vis spectra, elemental analysis and gel permeation chromatography (GPC). The polymers exhibit excellent solubility in common organic solvents, good film-forming properties, high glass transition temperature (T_g) in the range from 193 to 200 °C and thermal stability up to 290 °C. The polyimides P1 and P2 containing hetarylazo chromophores with large hyperpolarizability possess a high electro-optic (EO) coefficient (r₃₃), which is larger than that of the polyimide P3 attached DR1. Excellent temporal stability and low optical losses in the range of 1.9-2.1 dB/cm at 1.55 μm were observed for these polymers. Such new NLO fluorinated polyimides are distinguished by an excellent combination of NLO activity, temporal stability, and optical loss.     

Second-order nonlinear optical property of polyphosphazenes containing charge-transporting agents and indole-based chromophore

A new post functional strategy was developed to prepare polyphosphazenes with a high density of the indole based chromophore (nitro-indole or sulfonyl-indole chromophores) and carbazolyl side groups. Thus polyphosphazene (P1) with carbazolyl and indole groups was first prepared by direct nucleophilic substitution reaction with poly(dichlorophosphazene). Then, polyphosphazenes (P2-P4) containing charge-transporting agent (carbazolyl groups) and indole azo chromophores were synthesized via a post azo coupling reaction between P1 and p-nitrobezenediazonium fluoroborate or p-ethylsulfurylbenzenediazonium fluoroborate in N-methylpyrrolindone (NMP). The structures of P1-P4 were characterized, and the poled film of P2-4 revealed a resonant d₃₃ values in the range of 7-26 pm/V by second harmonic generation (SHG) measurements.     

Hg detection by aniline-based conjugated copolymers with high selectivity

Conjugated polymers (P1, P1L and P2-P5) constructed by alkynyl-substituted aniline and substituted arene analogs could be synthesized through Pd-catalyzed Sonogashira coupling. The responsive optical properties of poly(2-ethynyl aniline) (P1 and P1L for different molecular weights, P1L with longer chains on average) toward various metal ions (including Ni²⁺, Ag⁺, Cu²⁺, Zn²⁺, Fe³⁺, Fe²⁺, Mn²⁺, Na⁺, Ca²⁺, Pb²⁺, K⁺, Cr³⁺, Al³⁺, Cd²⁺, Pt²⁺, Au³⁺ and Tl³⁺) were investigated. Hg²⁺ exhibited the most pronounced fluorescence response of both P1 and P1L without interference from those coexistent ions due to aniline in the polymer backbone as the metal binding ligand, while other metal ions does not cause obvious change of fluorescence. Compared with P1, P1L exhibits better sensitivity toward Hg²⁺. Introducing pyridyl, thienyl or phenyl groups into the polymer backbone would weaken the quenching responses to Hg²⁺ compared with P1. The results indicated P1 and P1L could be used as a selective fluorescence sensor toward Hg²⁺.     

Polybinaphthyls incorporating chiral (R) or (S)-2,2′-binaphthyland oxadiazole moieties by Stille reaction

Chiral polymers P-1 and P-2 were prepared by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-1) with 2,5-bis[(4-tributylstannyl)phenyl]-1,3,4-oxadiazole (M-2) via Pd(PPh₃)₄ catalyzed Stille coupling reaction. 1,3,4-Oxadiazole unit not only has high electron affinity, high thermal and oxidative stability, but also serves as a good chromophore. Polymers have strong blue fluorescence due to the efficient energy migration from the extended π-electronic structure of the polymers to the chiral binaphthyl core and can be expected to have potential application in the materials of fluorescent sensors. Circular dichroism (CD) spectra of polymers P-1 and P-2 are almost identical except that they gave opposite signals at each wavelength. The long wavelengths CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and a high rigidity of the polymer backbone.     

Synthesis and characterization of side-chain liquid crystalline homopolymers and block copolymers containing biphenyl-4-ylthiophene and biphenyl-4-ylfluorene pendants

A series of new liquid crystalline homopolymers (P1 and P2) and block copolymers (P3 and P4) composed of methacrylates containing pendant biphenyl-4-ylthiophene (M1) and biphenyl-4-ylfluorene (M2) units were synthesized by atom transfer radical polymerization (ATRP). The number-average molecular weights (M_n) of the homopolymer (P2) and diblock copolymers (P3 and P4) were in the range of 5153-8713 g mol⁻¹ with polydispersity indices (PDIs) between 1.17 and 1.25. The thermal, mesogenic, and photoluminescence (PL) properties of all polymers were investigated. Except for the absence of mesogenic properties in block copolymer P4, polymers P1 and P3 possessed the smectic A phase and polymer P2 exhibited the nematic phase. Moreover, the mesomorphism and the layer d-spacing values of the smectic A phase in polymers P1 and P3 were confirmed and characterized by X-ray diffraction (XRD) patterns.     

Synthesis, characterization and third-order non-linear optical properties of novel fluorene monomers and their cross-conjugated polymers

We designed and synthesized two novel fluorene monomers of D-A-D (donor-acceptor-donor) type (M1 and M2), and their two corresponding polymers (PM1 and PM2) and a copolymer (CPM). These high molecular weight, film-forming polymers were obtained from metal-free, superacid-catalyzed reactions of the monomers with N-phenylisatin. The cubic NLO response (χ⁽³⁾) for these new compounds, in solid thin films, was measured through the use of third-harmonic generation (THG) Maker-Fringes technique at IR wavelengths given values of the order of 10⁻¹² esu from which, the corresponding second hyperpolarizabilities (γ) were estimated to be of the order of 10⁻³³ esu for monomers and 10⁻³¹ esu for polymers. Second hyperpolarizabilities have also been estimated theoretically at B3LYP/6-31G(d) level of theory in gas phase and related with the electronic structure of the synthesized molecules.     

Polybinaphthyls incorporating chiral 2,2′-binaphthyl and isoquinoline moieties by Sonogashira reaction

Polymers P-1, P-2, P-3, P-4 and P-5 were synthesized by the polymerization of 5,8-bis(ethynyl)isoquinoline (M-1) with (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-2), (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-2), (R)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-3), (S)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-3), and rac-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl (M-4) under Sonogashira reaction, respectively. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. CD spectra of polymers P-1 and P-2, P-3 and P-4 are almost identical except that they gave opposite signals at each wavelength. The long wavelength CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and the helical backbone in the polymer chain. All five polymers have strong blue-green fluorescence due to the efficient energy migration from the extended π-electronic structure of the repeating unit of the polymers to the chiral binaphthyl core and are expected to provide understanding of structure-property relationships of the chiral conjugated polymers.     

Synthesis and gas permeability of ester substituted poly(p-phenylene)s

Polymerizations of various ester substituted 2,5-dichlorobenzoates [substituent: linear alkyl groups (1a-f), branched alkyl groups (1g-l), cyclohexyl groups (1m-o), phenyl groups (1p-r), and oxyethylene units (1s-v)] were investigated with Ni-catalyzed/Zn-mediated system in 1-methyl-2-pyrrolidone (NMP) at 80 °C. Most of monomers bearing linear and branched alkyl groups successfully polymerized to give relatively high-molecular-weight polymers (M_n = 10,000-20,800). However, the molecular weight of the polymer having eicocyl groups was low because of steric hindrance of long alkyl chain. The polymerizations of cyclohexyl 2,5-dichlorobenzoate and phenyl 2,5-dichlorobenzoate produced low-molecular-weight polymers, while the polymerizations of monomers with alkyl cyclohexyl and alkyl phenyl groups proceeded to afford polymers with relatively high-molecular-weights. The polymers possessing oxyethylene units were obtained, but the molecular weights were low when the oxyethylene chains were long. The gas permeability of membranes of poly(p-phenylene)s with alkyl chains increased as increasing the length of alkyl chain. The membranes of poly(p-phenylene)s with phenyl groups and oxyethylene units exhibited high densities and relatively low gas permeability. However, the CO₂/N₂ separation factor of membrane of poly(p-phenylene) having oxyethylene units was as large as 73.6.     

Synthesis, characterization, and thermal properties of poly(siloxane-carborane)s

Three exactly alternating carborane-siloxane polymers P1, P2, and P3, have been synthesized by the polycondensation of 1,7-bis(dimethylhydroxylsilyl)-m-carborane and cyclotrisilazanes in the presence of (NH₄)₂SO₄. The reaction shows a new and convenient synthesis of poly(carborane-siloxane)s, and the first example of stoichiometric polycondensation of cyclosilazanes with diols. The new polymers P2 and P3 could be converted into thermosets at elevated temperature through the cross-linking of pendant vinyl groups. The structures of the polymers were fully characterized. Thermogravimetric analysis (TGA) showed the superior thermal stability of the polymers and thermosets, with their char yields of over 83% both in air (800 °C) and nitrogen (1000 °C). The microstructure of the chars was studied by scanning electron microscopy (SEM). It was found that the cross-linking of vinyl groups helped in enhancing the thermal stabilities of the polymers and keeping the integrity of the chars. The results suggest their potential utility under severe thermal and/or thermo-oxidative conditions.     

Synthesis and optoelectronic properties of luminescent copolyfluorenes slightly doped with thiophene chromophore

This paper describes the synthesis of new copolyfluorenes (P05-P5) slightly doped with 2,5-bis(2-phenyl-2-cyanovinyl)thiophene (GM, <3.4 mol%) and their application in electroluminescent (EL) devices. In film state, EL spectra of the copolyfluorenes are very different from photoluminescence (PL) spectra, which have been ascribed to charge trapping in GM and energy transfer from fluorene segments to GM chromophores. The maximum brightness and current efficiency of EL device from P05 (5230 cd/m², 0.65 cd/A) are significantly enhanced when compared with those from poly(9,9-dihexylfluorene) (PF) (1310 cd/m², 0.18 cd/A). The EL device using blend of P5 and PF (w/w = 10/1) as emitting layer exhibits near-white emission with CIE coordinate being (0.26, 0.32). The results demonstrate that the copolyfluorenes slightly doped with GM chromophore are promising emitting materials for optoelectronic devices.     

Synthesis and properties of helical polyacetylenes containing carbazole

Novel acetylene monomers containing carbazole with chiral menthyl and bornyl groups, 9-(1R,2S,5R)-menthyloxycarbonyl-2-ethynylcarbazole (1), 9-(1S,2R,5S)-menthyloxycarbonyl-2-ethynylcarbazole (2), 9-(1R,2S,5R)-menthyloxycarbonyl-3-ethynylcarbazole (3) and 9-(1S)-bornyloxycarbonyl-2-ethynylcarbazole (4) were synthesized and polymerized with a Rh catalyst to give the corresponding polymers [poly(1)-poly(4)] with moderate M_n value of (11.5-92.2) × 10³ in good yields (77-89%). CD spectroscopic studies revealed that poly(1), poly(2) and poly(4) took predominantly one-handed helical structure in CHCl₃, THF, toluene, and CH₂Cl₂, while poly(3) did not. Addition of methanol to CHCl₃ solutions of poly(1) and poly(2) resulted in the formation of aggregates showing smaller CD signals at 275 and 320 nm. The helical structure of poly(1) and poly(2) was very stable against heating. The polymers emitted fluorescence in 0.40-2.90% quantum yields. Poly(4) exhibited an obvious oxidation peak at 1.10 V. The polymers were thermally stable below 300 °C.     

Pd-catalyzed hydrosilylation polymerization of a dihydrosilane with diyne/triyne mixed systems affording crosslinked silylene-divinylene polymers and their properties

Treatment of a dihydrosilane (methylphenylsilane, 1) with mixtures of a diyne (p- or m-diethynylbenzene, 2a or 2b) and a triyne (1,3,5-triethynylbenzene, 3a or B,B′,B″-triethynyl-N,N′,N″-trimethylborazine, 3b; 1:2:3=100:95:5, 100:90:10, 100:80:20) in the presence of Pd-PCy₃ (Cy=cyclohexyl) catalyst gave new crosslinked silylenedivinylene polycarbosilanes. In TGA the resulting crosslinked polymers tended to show higher Td₅ values and higher char yields than the corresponding linear polymers. On the other hand, UV/vis absorption spectra of the crosslinked polymers obtained in the reactions of 2a or 2b with 3a exhibited increased broad peaks around 390 nm for 2a or 360 nm for 2b. Coincidently, their fluorescence spectra showed significant increase of the emission peaks in 400-550 nm. The crosslinked polymer derived from 2a and 3b, however, showed decrease of the absorption peak around 390 nm and profound depression of fluorescence peaks in 400-550 nm.     

Polymerization of o-diethynylbenzene and its derivatives controlled by transition metal catalyst systems

Polymerization of o-diethynylbenzene (1) by Rh and Ta catalysts resulted in the formation of structurally different polymers depending on the kind of catalyst. When a Rh catalyst was used, insoluble cross-linked poly(1) was formed, mainly consisting of alternating double bonds and the unreacted ethynyl group along with indene-type structure formed by intramolecular cyclization as a minor component. A Ta catalyst completely consumed both ethynyl groups in the polymerization of 1 to afford mainly highly cross-linked poly(1) containing trisubstituted benzene unit via intermolecular cyclization. 1-Ethynyl-2-phenylethynylbenzene (2) was polymerized by W and Mo catalysts to give soluble polymers with M_n of 6300-71,900 in good yields. Poly(2) obtained by Mo catalysts had alternating double bonds in the main chain and o-(phenylethynyl)phenyl group as side chains. Poly(2) formed by W catalysts predominantly contained a similar main-chain structure and also possessed the naphthalene-type cyclic unit formed by cyclization of the adjacent diethynyl groups as a minor part.     

Synthesis, characterization, and high gas permeability of poly(diarylacetylene)s having fluorenyl groups

Diarylacetylenes having fluorenyl groups and other substituents (trimethylsilyl, t-butyl, bromine, fluorine) (1a-1) were polymerized with TaCl₅-n-Bu₄Sn. Monomers 1a-l produced high molecular weight polymers 2a-l (M_w 5.1 × 10⁵-1.3 × 10⁶) in 12-59% yields. All of the polymers were soluble in common organic solvents, and gave tough free-standing membranes by the solution casting method. The onset temperatures of weight loss of polymers 2a-l in air were over 400 °C, indicating considerably high thermal stability. All the polymer membranes showed high gas permeability; e.g., the oxygen permeability coefficient (PO₂) of 2a was as large as 4800 barrers. Membrane 2d possessing two fluorine atoms at meta and para positions of the phenyl ring showed the highest oxygen permeability (PO₂ = 6600 barrers) among the present polymers.     

Synthesis and properties of cyclopentadithiophene-based poly(silarylenesiloxane) derivatives

Poly(silarylenesiloxane) derivatives with 4,4-dimethylcyclopenta[2,1-b:3,4-b′]dithiophene moiety, bearing dimethyl- (P1), methylphenyl- (P2) and diphenyl- (P3) substituents on silyl moieties, were prepared via polycondensation of the corresponding disilanol monomers, that is, 2,6-bis(dimethylhydroxysilyl)-4,4-dimethylcyclopenta[2,1-b:3,4-b′]dithiophene (M1), 2,6-bis(methylphenylhydroxysilyl)-4,4-dimethylcyclopenta[2,1-b:3,4-b′]dithiophene (M2), and 2,6-bis(diphenylhydroxysilyl)-4,4-dimethylcyclopenta[2,1-b:3,4-b′]dithiophene (M3), respectively. P1-P3 exhibited the good solubility in common organic solvents, such as benzene, toluene, chloroform, dichloromethane, THF, and so on. The glass transition temperatures (T_gs) of P1, P2 and P3 were determined by differential scanning calorimetry to be 56, 97 and 137 °C, respectively, depending on the substituent on the silyl moieties. No melting temperatures (T_ms) of P1, P2 and P3 were observed, suggesting the obtained P1-P3 are amorphous polymers. The temperatures at 5% weight loss (T_d5s) of P1, P2 and P3 were 460, 459 and 479 °C, respectively, indicating that the larger number of phenyl group on the silyl moieties resulted in the better thermostability. Bathochromic and hyperchromic effects were observed in the absorption and fluorescence spectra by introducing silyl substituents onto 4,4-dimethylcyclopenta[2,1-b:3,4-b′]dithiophene moiety. In addition, the bathochromic shift of the maximum absorption (λ_abs) and the increase in the fluorescence quantum yield (Φ_F) were observed by the introduction of phenyl group onto the silyl moieties.