Vinylene Units Research Articles

Stereoselective Cyclopolymerization of Diynes: Smart Materials for Electronics and Sensors

AbstractA series of heptadiynes was cyclopolymerized by Schrock initiators to produce poly(ene)s exclusively based on one single repetitive unit, i.e. 1,2‐cyclopent‐2‐enylenvinylenes. Polymers containing virtually solely 1,2‐cyclopent‐2‐enylenvinylene units were obtained by various routes, e.g. by low‐temperature‐initiated cyclopolymerization of diethyldipropargyl malonate (DEDPM). A chiral poly(ene) was prepared from 4‐(ethoxycarbonyl)‐4‐(1S, 2R, 5S)‐(+)‐menthoxycarbonyl‐1,6‐heptadiyne (ECMHD) to determine the configuration of the double bonds and the tacticity of the poly(ene) backbone. Poly(ECMHD) consisted of >96% 5‐membered rings and possessed a tactic, alternating cis‐trans structure. Alternatively, poly(DEDPM) exclusively based on 1,2‐(cyclopent‐1‐enylene)vinylene units was prepared using MoCl5‐n‐Bu4Sn‐EtOH‐quinuclidine (1:1:5:1) and MoOCl4‐n‐Bu4Sn‐EtOH‐quinuclidine (1:1:2:1). The initiator efficiency of MoOCl4‐n‐Bu4Sn‐EtOH‐quinuclidine (1:1:2:1) was as high as 91%, the highest value ever reported for such systems. Multistage polymerizations of DEDPM indicated for both initiator systems that the catalytic species were active for at least 6 hours in the presence of monomer yet did not fulfill the criteria of a truly living polymerization. Finally, a new modification of the Grubbs‐Hoveyda catalyst, Ru(CF3COO)2(CH‐2‐(2,4,5‐(MeO)3‐C6H3)(SIMes) (SIMes=1,3‐dimesityl‐4,5‐dihydroimidazol‐2‐ylidene) allowed the first ruthenium alkylidene‐catalyzed living cyclopolymerization of DEDPM. The different initiators, their properties, the resulting polymerization systems as well as the physical properties of the resulting poly(ene)s are summarized.

Electronic and structural effects on the nonlinear optical behavior in push-pull TTF/tricarbonyl chromiun arene complexes.

A novel D-pi-A system in which tetrathiafulvalene (TTF) and pi-extended TTFs as strong electron donors are covalently connected to a tricarbonyl (eta(6)-arene)chromium complex as the acceptor moiety through a systematically increased conjugated bridge of vinylene units (12a-c, 16a-c) have been synthesized by Wittig-Horner olefination reaction. The electronic spectra as well as the electrochemical data reveal a different behavior of TTF derivatives (12a-c) and of exTTF derivatives (16a-c). Cyclic voltammetry shows the influence of the tricarbonylchromium arene on the oxidation potentials in compounds 12a-c, and no remarkable effect is observed for exTTFs (16a-c). The nonlinear optical properties of 12a-c and 16a-c have been calculated by using the ab initio CPHF/6-31G//B3P86/6-31G model, and the time-dependent density functional theory (TD-DFT) method has been used for the calculation of the electronic transitions. The calculations reveal that an intraligand charge-transfer transition (ILCT) and the metal to ligand charge-transfer transition (MLCT) are responsible for the nonlinear response. In addition, the large angles formed by the ground-state dipole moment and the vectorial hyperpolarizability are responsible for the mubeta values determined experimentally by the EFISH technique.

Stepwise and directional synthesis of end-functionalized single-oligomer OPVs and their application in organic solar cells.

A new stepwise directional synthetic route to single-oligomer p-phenylenevinylenes (OPVs) has been developed. The first step in the reaction sequence is the condensation of a functionalized benzaldehyde with a novel monomer having a methyl phosphonate ester group in one end and an acetal-protected aldehyde at the other end of a stilbene core. Oligomerization then proceeds stepwise by alternating reaction of the previous aldehyde-terminated OPV fragment with the monomer and deprotection of the acetal. Thus, a series of OPVs with 3, 5, 7, 9, and 11 phenylene vinylene units has been prepared that has an electron-donating methoxy group at one end and an electron-accepting aldehyde group at the other end. Some examples where a dimethylamino group replaced the methoxy group were also prepared. The oligomer with seven phenylene vinylene units was then further derivatized at the aldehyde position to create a series of OPVs with a range of substituents from strongly electron-accepting nitrophenyl to electron-donating methoxyphenyl. Photovoltaic cells were assembled with the synthesized OPVs as the photoactive layer. Illumination under simulated sunlight (AM1.5) gave short circuit currents (Isc) in the range 0.015-0.5 mA cm(-2) and typical open circuit voltages (Voc) of 0.4-0.8 V. The maximum efficiency obtained was approximately 0.1%.

Stereoselective Hydroboration of Diynes and Triyne to Give Products Containing Multiple Vinylene Bridges: A Versatile Application to Fluorescent Dyes and Light-Emitting Copolymers

The Rh(I)-catalyzed hydroboration of a variety of aromatic diynes and a triyne afforded bis(boryl)- and tris(boryl)vinyl products. The hydroboration products underwent Suzuki cross-coupling reactions with a variety of substrates containing chromophore units to give fluorescent dye-substituted products. The hydroboration product also reacted with dibromoarenes to afford an oligomer with a vinylene unit along the oligomer backbone.

Novel Electroluminescent Polymers with Fluoro Groups in Vinylene Units

New electroluminescent polymers with fluoro groups in vinylene units, poly(p-phenylenedifluorovinylene) (PPDFV) and poly(2-dimethyloctylsilyl-p-phenylenedifluorovinylene) (DMOS−PPDFV), have been synthesized by GILCH polymerization. These polymers have been used as the electroluminescent (EL) layers in double-layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). PPDFV shows photoluminescence around λmax = 580 nm (exciting wavelength, 410 nm) and yellow electroluminescence around λmax = 565 nm. DMOS−PPDFV shows PL around λmax = 495 nm and green EL around λmax = 540 nm. The current−voltage−luminance (I−V−L) characteristics of the polymers show turn-on voltages of 3.0 V approximately. Two fluoro groups were introduced on every vinylene units of poly(p-phenylenevinylene) (PPV) and poly(2-dimethyloctylsilyl-1,4-phenylenevinylene) (DMOS−PPV) to give PPDFV and DMOS−PPDFV in an attempt to increase the electron affinity of the parent polymer. It was found that the efficiency of PLED of DMOS−PPDFV was about 7 times higher than that of DMOS−PPV.

Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes

AbstractThe influence of MgR2 and AlR3 additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s‐Bu2Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4‐ to 1,2‐ chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R3Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed.Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.

Synthesis and Properties of Poly(fluorene-alt-cyanophenylenevinylene)-Based Alternating Copolymers for Light-Emitting Diodes

The novel statistical alternating EL copolymers poly[bis{2-(4-phenylenevinylene)-2-cyanoethenyl}-9,9-dihexyl-9H-fluorene-2,7-yl-alt-1,4-phenylene vinylene] (polymer I), poly[bis{2-(4-phenylenevinylene)-2-cyanoethenyl}-9,9-dihexyl-9H-fluorene-2,7-yl-alt-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (polymer II), and poly[bis{2-(4-phenylenevinylene)-2-cyanoethenyl}-9,9-dihexyl-9H-fluorene-2,7-yl-alt-1,4-biphenylenevinylene] (polymer III) were synthesized using modified Heck coupling reactions, and their EL characteristics were investigated. These fluorene- and cyanophenylenevinylene-based alternating copolymers, which have strong electron-withdrawing CN groups on their vinylene units, were found to be completely soluble in common organic solvents and easily spin-coated onto indium−tin oxide (ITO) coated glass substrates. The HOMO and LUMO energy levels and the electrooptical properties of these copolymers can be tuned by varying the main-chain structures and the side-chain groups. These well-defined ...

Synthesis, characterization and photophysics of novel conjugated polymers with 1,3,4-oxadiazole pendant on a vinylene unit

Two novel conjugated polymers PV and PP were synthesized by Heck coupling or Ni(0)-mediated polymerization. They contain 3 or 1 vinylene bonds per repeat unit for PV and PP, respectively, as well as a pendant 1,3,4-oxadiazole on the vinylene bond. PV, that carry additional dodecyloxy pendant groups, showed higher solubility than PP being readily soluble in common organic solvents like THF, chloroform and 1,2-dichloroethane. PV had T g lower than 25 °C, while the T g for PP was 135 °C. No weight loss was observed up to 310–320 °C in N 2 and the anaerobic char yield was about 65% at 800 °C. PV and PP emitted blue-green and violet-blue light both in solution and thin film with PL emission maximum at 456–517 nm and 362–470 nm, respectively. The PL emission maximum of PV in solution was gradually red-shifted with increasing the solvent polarity. The PL intensity as well as the PL emission maximum of PV thin film was slightly affected upon annealing at 150 °C even for 60 min.

Syntheses and Characterization of Electroactive and Photoactive 2,7-Carbazolenevinylene-Based Conjugated Oligomers and Polymers

This study reports the first syntheses and characterization of 2,7-carbazolenevinylene-based oligomers and polymers. Their relatively straightforward syntheses are mainly based on Horner−Emmons or Knoevenagel coupling reaction leading to well-defined oligomers and polymers. As expected, introduction of vinylene and cyanovinylene unit into the polymer backbone decreases the band gap allowing a fine-tuning of the optical and electrical properties. These electroactive and photoactive organic materials exhibit promising performances in light-emitting devices and field-effect transistors. For instance, preliminary measurements using poly(N-(2-ethylhexyl)-2,7-carbazolenecyanovinylene-alt-2,5-dioctyloxy-1,4-phenylenevinylene) (PCCVP) have revealed orange-red emission with an intensity of 245 cd/m2 at 10 V, whereas p-type mobility of about 3.7 × 10-2 cm2/V·s and an on/off ratio as high as 106 were reached with 1,4-bis(vinylene-(N-hexyl-2-carbazole))phenylene (CPC).

Synthesis, Characterization, and Electroluminescence of New Conjugated Polyfluorene Derivatives Containing Various Dyes as Comonomers

Four new fluorene-based alternating polymers (PFR1-S, PFR2-S, PFR3-S, and PFR4-S) containing different comonomers (R1, R2, R3, and R4) have been designed, synthesized, and characterized. These polymers were found to be thermally stable and readily soluble in common organic solvents. Single layer LED devices fabricated from these polymers emitted bluish green to pure red light. Our results show that the color of the light emitted by the homopolymer, poly(9,9-dioctylfluorene-2,7-diyl) (PDOF), can be tuned by incorporating R1, R2, R3, and R4 comonomers, which have narrower band gaps. The absorption and emission maxima of the copolymers varied according to the position of the cyano group in the vinylene unit (α- or β-position) and the type of incorporated aromatic group (thiophene or phenylene). Notably, PFR4-S showed pure red emission (CIE coordinate values x = 0.66, y = 0.33) that is almost identical to the standard red (0.66, 0.34) demanded by the National Television System Committee. PFR3-S also exhibited pure red emission (chromaticity values x = 0.63, y = 0.38), and its maximum luminance and maximum external quantum efficiency were approximately 3100 cd/m2 at 6 V and 0.46% at 4 V, respectively.

Yellow Light-Emitting Poly(p-phenylenevinylene) Derivative with Balanced Charge Injection Property

A new luminescent polymer, poly{1,4-phenylene-1,2-ethenediyl-2'-[2"-(4'"-octyloxyphenyl)-(5"-yl)-1",3",4"-oxadiazole]-1,4-phenylene-1,2-ethenediyl-2,5-bis-dodecyloxy-1,4-phenylene-1,2-ethenediyl} (Oxd-PPV), was synthesized by the Heck coupling reaction. Electron withdrawing pendant, conjugated 1,3,4-oxadiazole (Oxd), is on the vinylene unit. The band gap of the polymer figured out from the UV-visible spectrum was 2.23 eV and the polymer film shows bright yellow emission maximum at 552 nm. The electroluminescence (EL) maximum of double layer structured device (ITO/PEDOT:PSS/Oxd-PPV/Al) appeared at 553 nm. Relative PL quantum yield of Oxd-PPV film is 3.6 times higher than that of MEH-PPV film. The HOMO and LUMO energy levels of Oxd-PPV figured out from the cyclic voltammogram and the UV-visible spectrum are -5.32 and -3.09 eV, respectively, so that more balanced hole and electron injection efficiency can be expected compared to MEH-PPV. A double layer EL of Oxd-PPV has an maximum efficiency of 0.15 cd/A and maximum brightness of 464 cd/<TEX>$m^2$</TEX>.

Study on chain transfer reaction of poly(vinyl acetate) radical with poly(vinyl alcohol) in a homogeneous system

The first purpose of this study is to obtain effectively the graft copolymer of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc). Polymerization of VAc in the presence of PVA in dimethyl sulfoxide (DMSO) was investigated. The second purpose of the study is to obtain a PVA having a long branch whose properties have not been clarified yet. By hydrolyzing the PVAc portion in the graft copolymer, the PVA having a long branch might be obtained. The polymerization system was thought to be homogeneous since DMSO is a common solvent for PVA and PVAc at 60°C. Prior to the experiment, solution polymerization of VAc in DMSO was carried out in the absence of PVA to know the chain transfer constant (C S) to DMSO. The C S value was determined to be 0.7×10-4. Then the chain transfer constant to PVA (C P) on the basis of monomer unit was measured to be 9.9×10-4. The C P value was much smaller than the value we had expected, since the C S to isopropanol, whose structure resembles that of the vinyl alcohol unit in PVA, had been reported to be about 5-times larger than this. The reason of the rather smaller value of C P appeared arise from the substantial decrease in concentration of the reactive sites that are buried in the polymer coil. The aimed graft copolymer of PVA and PVAc, as well as the PVA having a long branch, was proved to be rather difficult to obtain, since the reactivity of PVA molecule in the chain-transfer reaction is much lower than that of isopropanol.

Probing charge separation in structurally different C60/exTTF ensembles.

The scope of the present work is to highlight the effects stemming from different C60/exTTF linkages (exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene)-either via an anthracene unit or a dithiole ring. Particular emphasis is placed on photoinduced electron-transfer features. Therefore, we devised a new series of C60-exTTF ensembles, synthesized via 1,3-dipolar cycloaddition and Diels-Alder cycloaddition reactions, in which exTTF units are separated from C60 by two single bonds (3a-c, 4), one vinylene unit (5a), or two vinylene units (5b). The cyclic voltammetry reveals an amphoteric redox behavior with remarkably strong electron-donor ability of the trimethyl-substituted exTTF moiety in 4 and 5a,b. Steady-state and time-resolved photolytic techniques show that the fullerene singlet excited state in (3a-c, 4, and 5a,b) is subject to a rapid electron-transfer quenching. The resulting charge-separated states, that is C60*(-)-exTTF*+, were identified by transient absorption spectroscopy. We determined radical pair lifetimes of the order of 200 ns in benzonitrile. This suggests (i) that the positive charge of the exTTF*+ is delocalized over the entire donor rather than localized on one of the 1,3-dithiole rings and (ii) that linking exTTF via the anthracene or 1,3-dithiole ring has no appreciable influence. Increasing the donor-acceptor separation via implementing one or two vinylene units as spacers led to improved radical pair lifetimes (5a: tau = 725 ns; 5b: tau = 1465 ns).

χ(3) measurements in novel poly(2′,5′-dioctyloxy-4,4′,4″-terphenylenevinylene) using the Z-scan technique

We investigated the third-order nonlinear optical (NLO) properties of three poly(2′,5′-dioctyloxy-4,4′,4″-terphenylenevinylene)s having different cis/ trans-vinylene ratios. The nonlinear measurements were performed at λ=532 nm in chloroform solutions using single-beam Z-scan technique with picosecond laser pulses. All the investigated polymers exhibit a moderate two-photon resonance at this wavelength. On the contrary, the magnitude of the nonlinear refractive index is high and shows a considerable dependence on the cis/ trans ratio of the double bonds. The largest third-order nonlinear optical susceptibility, | χ (3)|=(5±1)×10 −10 esu, was measured for a polymer with all monomers having vinylene unit in trans-configuration.

Highly Efficient Novel Poly(p-phenylenevinylene) Derivative with 1,3,4-Oxadiazole Pendant on a Vinylene Unit

The conjugated 1,3,4-oxadiazole (OXD) pendants on the vinylene unit of the polymer lead to an increase in electron affinity and decrease in interchain interaction. The light-emitting device based on OXD−PPV shows bright yellow emission with an efficiency of 0.43% and a brightness of 5140 cd/m2.

Stereocontrolled synthesis of ( E)- and ( Z)-poly( p-phenylenevinylene)s via ruthenium-catalyzed hydrosilylation of p-diethynylbenzene

Stereocontrolled synthesis of poly(phenylenevinylene)s (PPVs) with ( E)- and ( Z)-vinylene units has been examined. Ruthenium complex-catalyzed hydrosilylation of p-diethynylbenzene with HSiMe 2Ar (Ar=2-thienyl (Th), 3,5-(CF 3) 2C 6H 3) proceeds readily in CH 2Cl 2 at room temperature to give ( E, E)- or ( Z, Z)-bis(2-silylethenyl)benzenes ( 3a, 3b) in 89–40% yields. The geometries of 3a and 3b are clearly dependent on ruthenium catalysts employed. Thus, RuHCl(CO)(PPh 3) 3 forms ( E, E)-isomers in over 99% selectivities, whereas RuCl 2(CO)(PPr i 3) 2 affords ( Z, Z)- 3a and 3b with 92 and 91% geometrical purities, respectively. The ( E, E)- and ( Z, Z)-isomers of 3a and 3b undergo polycondensation with 2,5-dioctyloxy-1,4-diiodobenzene in THF in the presence of a palladium catalyst ([PdCl(η 3-allyl)] 2, Pd(dba) 2) and tetrabutylammonium fluoride hydrate, giving ( E)-rich and ( Z)-rich PPVs in high yields.

Effect of the molecular weight of poly(ethylene glycol) on the plasticization of green sheets composed of ultrafine BaTiO 3 particles and poly(vinyl butyral)

The effect of the molecular weight (MW) of poly(ethylene glycol) (PEG) on the plasticization of poly(vinyl butyral) (PVB) binder in green BaTiO 3 sheets prepared with PEG with MW values of 400 and 1530 was investigated. The MW of PEG had a profound effect on the rheological properties of the suspension as well as the physical properties of the green sheet. The suspension viscosity decreased with decreasing MW of PEG for shear rates above 4 s −1. PEG 400 gave rise to a higher degree of plasticization of the green sheet than PEG 1530. This was due to the reduction in hydrogen bonding between the vinyl alcohol units in the PVB binder in the green BaTiO 3 sheet, as identified by FT-IR spectroscopy. As the MW of the PEG decreased, the green BaTiO 3 sheets exhibited a lower glass transition temperature, and a noticeably more ductile behavior. These results indicate that the green sheets became more flexible due to a higher plasticizing effect. However, laminated green BaTiO 3 sheets prepared with PEG 1530 showed delamination defects that were observed at a cut surface, which arose because of the low plasticization. This suggests that PEG 1530 has limited utilization as a plasticizer for the BaTiO 3/PVB binder system.

Sulfonate and Sulfonamide Activated Olefins and Acetylenes in [4+2] Cycloaddition Reactions

Sulfonate and sulfonamide are electron withdrawing activators for both vinyl and acetylenic units. These vinyl (acyclic and cyclic) and acetylenic sulfonates and sulfonamides are versatile dienophiles in inter- and intramolecular Diels-Alder reactions, as well as dipolarophiles in 1,3-dipolar cycloadditions. Asymmetric versions of these cycloaddition reactions are also known. Further manipulation of the cycloaddition products afforded interesting compounds that are useful synthons and building blocks in natural product synthesis and asymmetric synthesis.

Electrosynthesis and characterisation of Poly(paraphenylene vinylene C60) films

The electrochemical reductive polymerization of a co-polymer of phenylene vinylene units and C 60 was studied. The fullerene is introduced into the polymer synthesis as a film on the electrode substrate. During reduction the film is dissolved and the reduced fullerene species interact with the PPV precursor in solution and as a result a film is formed on the substrate. The coupling reaction between the reduced species should lead to a material where the fullerene units are incorporated into the main polymer chain. The films are characterised by cyclic voltammetry and by FTIR and Raman spectroscopy.

First Controlled Cyclopolymerization of Diethyl Dipropargylmalonate by MoCl5−n-Bu4Sn−EtOH−Quinuclidine and MoOCl4−n-Bu4Sn−EtOH−Quinuclidine To Give Highly Regular Polyenes Consisting Exclusively of 1,2-(Cyclopent-1-enylene)−Vinylene Units

Diethyl dipropargylmalonate (DEDPM) was cyclopolymerized by MoCl5−n-Bu4Sn−EtOH−quinuclidine (1:1:5:1) and MoOCl4−n-Bu4Sn−EtOH−quinuclidine (1:1:2:1), respectively, to produce poly(DEDPM) exclusively based on 1,2-(cyclopent-1-enylene)vinylene units (EtOH = ethanol). The exact ratio of five- to six-membered rings was determined by quantitative 13C NMR measurements. The initiator efficiency of MoOCl4−n-Bu4Sn−EtOH−quinuclidine (1:1:2:1) was as high as 91%, the highest value ever reported for such systems, whereas the efficiency for the corresponding MoCl5-based initiator was ≤67%. The absorption maximum λmax for poly(DEDPM) was 587 nm. A maximum effective conjugation length (Neff) of 49 was estimated therefrom. Molecular weights and polydispersity indices (PDIs) of the polymers were determined in CHCl3 by size exclusion chromatography (SEC) vs polystyrene (PS). Additionally, light-scattering (LS) data were collected at λ = 690 nm in order to calculate absolute molecular weights. Polydispersities ≤1.9 were obt...