A fluorescence sensor based on chiral polymer for highly enantioselective recognition of phenylalaninol

The chiral polymer P-1 incorporating (S)-2,2′-binaphthol (BINOL) and (S)-2,2′-binaphthyldiamine (BINAM) moieties in the main chain of the polymer backbone was synthesized by the polymerization of (S)-6,6′-dibutyl-3,3′-diformyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-binaphthyldiamine (S-M-2) via nucleophilic addition-elimination reaction, and the chiral polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence intensity of the chiral polymer P-1 exhibits gradual enhancement upon addition of (d)- or (l)-phenylalaninol and keeps nearly a linear correlation with the concentration molar ratios of (d)- or (l)-phenylalaninol. The value of enantiomeric fluorescence difference ratio (ef) is 6.85 for the chiral polymer on (d)-phenylalaninol. On the contrary, the chiral polymer P-2 shows no obvious fluorescence response toward either (d)- or (l)-phenylalaninol.     

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 properties of ornithine- and lysine-based poly(N-propargylamides). Responsiveness of the helical structure to acids

Ornithine- and lysine-based novel N-propargylamides, N-α-tert-butoxycarbonyl-N-δ-fluorenylmethoxycarbonyl-l-ornithine-N′-propargylamide (1), N-α-tert-butoxycarbonyl-N-?-fluorenylmethoxycarbonyl-l-lysine-N′-propargylamide (2), N-α-fluorenylmethoxycarbonyl-N-δ-tert-butoxycarbonyl-l-ornithine-N′-propargylamide (3), and N-α-fluorenylmethoxycarbonyl-N-?-tert-butoxycarbonyl-l-lysine-N′-propargylamide (4) were synthesized and polymerized with a rhodium catalyst. Polymers with moderate molecular weights were obtained in good yields. Poly(1)-poly(4) showed strong Cotton effects in THF, whose sign and wavelength depended on the substituents. They were satisfactorily converted into the corresponding polymers [poly(1a)-poly(4a)] with free amino groups. Poly(1a) and poly(2a) also formed a helix, while poly(3a) and poly(4a) did not. Poly(1a) and poly(2a) decreased the CD intensity by the addition of m- and o-phthalic acids.     

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 of 1,9-bis[glycidyloxypropyl]penta(1′H,1′H,2′H,2′H-perfluoroalkylmethylsiloxane)s and copolymerization with piperazine

A series of 1,9-bis[glycidyloxypropyl]pentasiloxanes (IV-VI) were prepared by the platinum catalyzed hydrosilylation of 1,9-dihydridodecamethylpentasiloxane (I), 1,9-dihydrido-3,5,7-tris(3′,3′,3′-trifluoropropyl)heptamethylpentasiloxane (II), and 1,9-dihydrido-3,5,7-tris(1′H,1′H,2′H,2′H-perfluorooctyl)heptamethylpentasiloxane (III) with allyl glycidyl ether. Subsequently, IV-VI were copolymerized with piperazine to form high molecular weight copoly(carbosiloxane)s (VII-IX). The structures of the 1,9-bis[glycidyloxypropyl]penta-siloxanes (IV-VI) and copoly(carbosiloxane)s (VII-IX) were determined by ¹H, ¹³C, ²⁹Si, and ¹⁹F NMR as well as IR spectroscopy. The molecular weight distributions (M_w/M_n) of VII-IX have been characterized by gel permeation chromatography and their thermal properties measured by differential scanning calorimetry and thermal gravimetric analysis.     

Synthesis and properties of chiral helical polymers based on optically active polybinaphthyls

The chiral polymer P-1 was synthesized by the polymerization of (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bisoctoxy-1,1′-binaphthyl (R-M-1) with 5,5′-divinyl-2,2′-bipyridine (M-1)via Pd-catalyzed Heck reaction. P-2 and P-2′ were prepared by Wittig-Horner reaction of (R)-6,6′-dibutyl-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (R-M-2) with 5,5′-bis (diethylphosphonomethyl)-2,2′-bipyridine (M-2) in the presence of EtONa or NaH, respectively. P-3 was synthesized by Wittig-Horner reaction of (R)-6,6′-di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (R-M-3) with M-2 using NaH as a base. The four polymers have strong blue-green fluorescence due to the extended π-electronic structure between the chiral model compounds (R)-6,6′-dibutyl-/di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl (R-1 or R-2) and the conjugated linker 2,2′-bipyridyl group via vinylene bridge. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. Based on the great differences of specific rotation values and CD spectra, P-1 and P-2 may adopt a zigzag chain configuration, while P-2′ and P-3 may adopt a helical configuration. The responsive optical properties of the two chiral helical polymers P-2′ and P-3 on transition metal ions were investigated by fluorescence, UV-vis and CD spectra. The results show that Ag⁺ and Ni²⁺ lead to nearly complete fluorescence quenching of P-2′ and P-3, Cu²⁺ and Fe²⁺ can cause obvious fluorescence quenching, but Zn²⁺ and Cd²⁺ can only produce slight fluorescence quenching. Ag⁺, Ni²⁺, Cu²⁺ and Fe²⁺ can also lead to the obvious changes of UV-vis spectra of P-2′ and P-3. On the contrary, Zn²⁺ and Cd²⁺ cause little changes. Most importantly, the CD intensities and wavelengths of the chiral helical polymers P-2′ and P-3 exhibit the pronounced changes upon addition of Ag⁺ and Ni²⁺.     

Tyrosine-based poly(m-phenyleneethynylene-p-phenyleneethynylene)s. Helix folding and responsiveness to a base

The Sonogashira-Hagihara polymerization of 3′,5′-diiodo-N-α-tert-butoxycarbonyl-l-tyrosine methyl ester (1) and 3′,5′-diiodo-N-α-tert-butoxycarbonyl-O-methyl-l-tyrosine methyl ester (2) with para-diethynylbenzene (3) was carried out to obtain optically active poly(m-phenyleneethynylene-p-phenyleneethynylene)s [poly(1) and poly(2)] with M_n’s ranging from 9900 to 15,000 in 80-87% yields. Poly(1) exhibited intense CD signals in DMSO and THF, but did not in CH₂Cl₂, indicating that it took a predominantly one-handed helical conformation in the former two solvents. On the other hand, there was no evidence for poly(2) to take a helical structure in these solvents. Poly(1) turned the CD sign at 390 nm from plus to minus in DMSO/H₂O = 9/1 (v/v) by the addition of NaOH. Alkaline hydrolysis of ester moieties of poly(1) and poly(2) gave the corresponding polymers having carboxy groups [poly(1a) and poly(2a)]. Poly(1a) and poly(2a) increased the CD intensity by the addition of NaOH.     

A fluorene-containing water-soluble poly(p-phenyleneethynylene) derivative: Highly fluorescent and sensitive conjugated polymer with minor aggregation in aqueous solution

A novel cationic fluorene-containing water-soluble poly(p-phenyleneethynylene) (PPE) derivative, poly[(9,9-bis{6′-[(N,N-diethyl)-N-methylammonium]hexyl}-2,7-fluorenyleneethynylene)-alt-co-(2,5-bis{3′-[(N,N-diethyl)-N-methylammonium]-1′-oxapropyl}-1,4-phenylene)] tetraiodide (P1′), was synthesized through Sonogashira reaction and a post-polymerization treatment. P1′ emits bright blue fluorescence in H₂O with a high photoluminescence quantum yield (Φ_pl=26%). Studies on the optical properties and quenching experiments with in H₂O and MeOH show that P1′ presents minor aggregation and high Stern-Volmer constant (K_sv=2.4×10⁸ M⁻¹) in aqueous solution. The remarkably reduced tendency towards aggregation, relative to previously reported water-soluble PPEs, made the optical properties of P1′ almost insensitive to the disturbance from the common ions (non-quencher) in the solution.     

A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

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.     

Effects of internal linkage groups of fluorinated diamine on the optical and dielectric properties of polyimide thin films

To investigate the difference of the trifluoromethyl (CF₃) group and ether group affecting the optical property of fluorinated polyimides (PIs), we prepared 4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether (4) with three ether groups and 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane (5) with four CF₃ groups with 2-chloro-5-nitrobenzotrifluoride and 4,4′-dihydroxydiphenyl ether or 2,2-bis(4-hydroxyphenol)hexafluoropropane. Two series of organosoluble and light-colored PIs (4a-4c, 5a-5c) were synthesized from 4 and 5 with various aromatic dianhydrides: 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA) (a), 4,4-oxydiphthalic anhydride (ODPA) (b), and 4,4-hexafluoroisopropylidenediphthalic anhydride (6FDA) (c), prepared through a typical two-step polymerization method. These PIs were soluble in amide polar solvents and even in less polar solvents. The glass-transition temperatures (T_g) of 4a-5c were 221-249 °C and the 10% weight-loss temperatures were above 530 °C. Their films had cutoff wavelengths between 339 and 399 nm and yellowness index ranges from 1.95 to 42.60. The dielectric constants estimated from the average refractive indices are 2.59-2.93 (1 MHz). In a comparison of the PI series based on 4, 5, and 4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6), we found that the CF₃ group and ether group on the diamine had almost same effect in lowering the color, but the ether group had better thermal stability. The color intensity of the three PI series was lowered in the following order: 6 > 4 > 5. The PI 5c, synthesized from diamine 5 and dianhydride c, had six CF₃ groups in a repeated segment and ether group at the same time, so it exhibited the lightest color among the three series.     

Three new five-coordinated mercury (II) dyes: Structure and enhanced two-photon absorption

A new donor-bridge-acceptor (D-π-A) type ligand (L: 4′-(4-[4-(imidazole)styryl]phenyl)-2,2′:6′,2″-terpyridine) with two-photon absorption and coordination ability was designed and synthesized. Self-assembly of the ligand with HgX₂ (X = Cl, Br, I) yielded a series of new coordination complexes (Dyes 1-3) with five-coordinated mercury (ΙΙ), which were characterized by single crystal X-ray diffraction determination. Solvent molecules and various weak interactions, including hydrogen bonds (C-H···N, C-H···X) and π-π interactions played significant roles in the final topological structures. Linear and nonlinear optical properties of the ligand and three dyes were described. Experimental results revealed that two-photon absorption cross sections of three dyes are extraordinary stronger than that of ligand.     

Spectral properties of chalcone containing triphenylamino structural unit in solution and in polymer matrices

Novel chalcones (3-phenyl-1-phenylprop-2-en-1-ones) substituted on one end (position 3) with electron donating diphenylaminophenyl substituent and on the other end (position 1) with thiophenes with variable electronic effects (CH-1-CH-5) were prepared. The spectral properties of these molecules in solvents such as chloroform, cyclohexane, acetonitrile, methanol and incorporated into polymer matrices of polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) were compared with those of 3-[4-(N,N-dimethylamino)-phenyl]-1-phenylprop-2-en-1-one (CH-1m) and 3-[4-(N,N-dimethylamino)phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (CH-2m). The longest wavelength absorption band of model chalcones CH-1m and CH-2m was in the range of 400-420 nm and did not appear to be influenced by the medium. The fluorescence increased with the addition of acetonitrile, while it was effectively quenched in methanol. The strong electron-attracting nitro group quenched the fluorescence of CH-2m in nearly all solvents. In contrast, the fluorescence became more intense when the molecule was incorporated in a polymer matrix. The longest wavelength absorption band of novel chalcones was observed in the range of 410-450 nm in all media. The fluorescence of chalcones was red-shifted to the range of 530-575 nm and was most intense in chloroform. The quantum yield of fluorecence was the highest in chloroform for the chalcone with a methyl-thiophene (0.49) and low for the chalcone with a fluorenyl-thiophene group (0.07). The fluorescence of all chalcones (CH-1-CH-5) was effectively quenched in polar acetonitrile and methanol, and was less intense relative to chloroform when incorporated into a polymer matrix and more intense relative to other solvents. The lifetime of fluorescence was in the range of 1-4 ns. The Stokes shift was in the range of 4000-5000 cm⁻¹ in chloroform, and lower in all other media. The spectral behavior of model chalcones CH-1m and CH-2m and novel chalcones with diphenylamino substituents was similar, producing observable fluorescence in several polymer matrices. The effect of the solvent on the fluorescence is discussed in terms of negative and positive solvatokinetic effects.     

Redox and catalytic properties of new polypyrrole modified electrodes functionalized by [Ru(bpea)(bpy)H2O] complexes; bpea=N,N′-bis(2-pyridylmethyl)ethylamine, bpy=2,2′-bipyridine

New ruthenium(II) complexes containing one or two pyrrole-functionalized polypyridylic ligands have been prepared in order to study their electrochemical behaviour in heterogeneous phase, after anodic polymerization from CH₂Cl₂ solution on an electrode surface. Complexes containing one pyrrole unit have general formula [Ru(bpea-pyr)(bpy)(L)]²⁺ (bpea-pyr=N-[3-bis(2-pyridylmethyl)aminopropyl]pyrrole, bpy=2,2′-bipyridine, L=Cl, complex 3, or L=H₂O, complex 1), whereas compounds having two pyrrole units correspond to [Ru(bpea-pyr)(bpy-pyr)(L)]²⁺ (bpy-pyr=4-methyl-4′-pyrrolylbutyl-2,2′-bipyridine, L=Cl, complex 4, or L=H₂O, complex 2). Upon oxidative polymerization, all complexes form highly stable polypyrrolic films on a graphite disk electrode surface. An electrode modified with complex 2 polypyrrole coating film, C/poly-2, has been tested as heterogeneous catalyst for the oxidation of benzyl alcohol, showing a remarkably high efficiency and notably improving the results obtained with analogous complexes in homogeneous phase.     

Synthesis and electrochromic properties of aromatic polyimides bearing pendent triphenylamine units

A series of aromatic polyimides with pendent triphenylamine group were synthesized from equimolar mixtures of 4,4′-oxydianiline (ODA) and 4-(3,5-diaminobenzamido)triphenylamine (4), 4-(3,5-diaminobenzamido)-4′,4″-di-tert-butyltriphenylamine (t-Bu-4) or 4-(3,5-diaminobenzamido)-4′,4″-dimethoxytriphenylamine (MeO-4) with two aromatic tetracarboxylic dianhydrides (DSDA or 6FDA) via a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical imidization. These polyimides exhibited good solubility in polar organic solvents and could be solution-cast into flexible and strong films. They showed excellent thermal stability, with T_g values in the range of 284–309 °C. The polyimides derived from diamines t-Bu-4 and MeO-4 exhibited reversible electrochemical oxidation, accompanied by strong color changes with high contrast ratio and electrochromic stability. For the polyimides derived from diamine 4, the coupling reaction between the triphenylamine radical cations occurred during the oxidative process forming a tetraphenylbenzidine structure, which resulted in an additional oxidation state and color change together with enhanced near-IR absorption at fully oxidized state.     

Aromatic diamine-based benzoxazines and their high performance thermosets

Four high-purity aromatic diamine-based benzoxazines (13-16), which could not easily be synthesized by traditional approaches, were successfully synthesized by a facile, widely useful three-step synthetic method using four typical aromatic diamines - 4,4′-diamino diphenyl methane (1), 4,4′-diamino diphenyl sulfone (2), 2,2-bis(4-(4-aminophenoxy)phenyl)propane (3), and bis(4-(4-aminophenoxy)phenyl)ether (4), respectively, as starting materials. The structures of the monomers (5-16) were confirmed by ¹H, ¹³C, ¹H-¹H and ¹H-¹³C NMR spectra. Their high performance thermosets, P(13-16), were obtained by thermal curing of benzoxazines (13-16), and their properties were studied and compared with polymer derived from bis(3,4-dihydro-2H-3-phenyl-1,3-benzoxazinyl)methane (F-a), a typical aromatic biphenol-based benzoxazine. Among the benzoxazines, 13 and F-a are constitutional isomers, but the T_g value and 5% decomposition temperature of P(13) are 53 and 111 °C, respectively, higher than those of P(F-a), demonstrating the power of the molecule-approach to enhance the thermal properties. Because of the large varieties of aromatic diamines, this approach can increase the molecule-design flexibility of benzoxazines.     

Preparation of π-conjugated polymers consisting of 2-decylbenzimidazole and thiophene units and chemical properties of the polymers

Polycondensation by Stille coupling of 2-decyl-4,7-dibromobenzimidazoles and N-methyl-2-decyl-4,7-dibromobenzimidazole with 2,5-bis(trimethylstannyl)thiophene and 5,5′-bis(trimethylstannyl)-2,2′-bithiophene gave the corresponding π-conjugated polymers, poly(2-decylbenzimidazole-4,7-diyl-thiophene-2,5-diyl) 1b, poly(2-decylbenzimidazole-4,7-diyl-bithiophene-2,5-diyl) 1c and poly(N-methyl-2-decylbenzimidazole-4,7-diyl-thiophene-2,5-diyl) 2b, in 98-99% yields. The polymers 1b and 2b were fully soluble in CF₃COOH, and partially soluble in DMF (about 60 and 40% for 1b and 2b, respectively) and NMP (about 70 and 40%, respectively). The NMP soluble part of 1b and DMF soluble part of 2b gave values of 0.36 and 0.24 dl g⁻¹ in NMP and DMF, respectively. The DMF soluble part of 1b, 1c and 2b showed absorption peaks at about 458, 465 and 388 nm, respectively, in DMF. In an alkaline medium the absorption peaks of 1b and 1c are shifted to a longer wavelength by 92-101 nm; the observed shifts in the acidic medium and alkaline medium were much larger than those observed with usual benzimidazoles with low molecular weights. Packing structures of 1b, 1c and 2b are discussed based on their XRD patterns.     

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.     

Fluorescent chemosensor for metal ions based on optically active polybinaphthyls and 1,3,4-oxadiazole

Linear chiral polymers P-1 and P-2 were synthesized by the polymerization of (R)-5,5′-dibromo-6,6′-di(4-methylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl (R-M-1) with 2,5-di(4-vinylphenyl)-1,3,4-oxadiazole (M-2) and 2,5-di(4-tributylstannylphenyl)-1,3,4-oxadiazole (M-3) via Heck and Stille cross-coupling reaction, respectively. The chiral conjugated polymer P-1 can show strong green-blue fluorescence, and the chiral polymer P-2 shows strong blue fluorescence. While the conjugated polymers P-1 and P-2 were used as fluorescent chemosensor for metal ions, their fluorescence can be efficiently quenched on the addition of different metal ions. The obvious quenching effect of the polymers P-1 and P-2 indicates that the intramolecular photoinduced electron transfer (PET) or photoinduced charge transfer (PCT) between the polymer backbone and receptor-ions in the main chain of fluorescent chemosensor can lead to the pronounced fluorescence quenching. The results also show that the chiral polymers P-1 and P-2 incorporating 1,3,4-oxadiazole moiety as the recognition site can act as a special fluorescent chemosensor for the appropriate detection of the sensitive and selective sense of metal ions.     

Copoly(1,3,4-oxadiazole-ether)s containing phthalide groups and thin films made therefrom

A series of aromatic copolyethers containing 1,3,4-oxadiazole rings and phthalide groups was prepared by nucleophilic substitution polymerization technique of phenolphthalein, 1, or of an equimolecular amount of 1 and different bisphenols 2, such as: 4,4′-isopropylidenediphenol, 4,4′-(hexafluoroisopropylidene)diphenol, 4,4′-(1,4-phenylene-diisopropylidene)bisphenol, 4,4′-cyclohexylidene-bisphenol and 2,7-dihydroxynaphthalene, with 2,5-bis(p-fluorophenyl)-1,3,4-oxadiazole, 3. The polymers were easily soluble in polar solvents such as N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and chloroform and can be cast from solutions into thin flexible films. They showed high thermal stability, with decomposition temperature being above 400 °C. The polymers exhibited a glass transition temperature in the range of 220-271 °C, with reasonable interval between glass transition and decomposition temperature. Electrical insulating properties of some polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature. The values of the dielectric constant at 10 kHz and 20 °C were in the range of 2.98-3.15.