Gerhard Koßmehl

Reactive groups on polymer coated electrodes, 7. New electrogenerated electroactive polythiophenes with different protected carboxyl groups

By the protection of the carboxyl group of 3-thiopheneacetic acid with differently substituted benzyl groups a series of new thiophene derivatives were synthesized. While 3-thiopheneacetic acid is not electropolymerizable, the new obtained monomers can be easily electrooxidized to form stable electroactive polymers. The electrochemical characterizations show that the substitution of the benzyl groups exerts little effect on the electropolymerization process and that the obtained polymers exhibit the typical properties of polythiophene derivatives, e. g., redox behavior and electrochromism. SEM studies show that all synthesized monomers possess a very good film formability and the resulting polymers exhibit a rather compact and homogeneous morphology on the Pt electrodes also containing scattered particles. Using p-nitrobenzyl-protected polymer as an illustrative example, it was demonstrated that the used protecting group can be easily split off in the solid state and the desired reactive carboxyl group can be produced on the polymer surface. Therefore, through the protection of the carboxyl group, the electropolymerization and the following removal of the protecting group, a new type of polymer matrix material with reactive carboxyl groups was simply prepared by using commercially available 3-thiopheneacetic acid monomer.

Reactive groups on polymer coated electrodes, 8. Novel conducting polymer interfaces produced by electrochemical copolymerization of functionalized thiophene activated esters with 3-methylthiophene

With the synthesis of two new functionalized thiophene activated esters and their electrocopolymerization with 3-methylthiophene, two types of redox active polymers have been prepared. FTIR studies of the resultant polymers reveal that both types of activated ester groups withstand the applied electrooxidative conditions and are correctly integrated into the corresponding polymers. The electrocopolymerization experiments show that the composition of the obtained polymers strongly depends on the ratio of the components in the reaction medium. With the increase of the ratios of pentafluorophenyl thiophene-3-acetate/3-methylthiophene or succinimido thiophene-3-acetate/3-methylthiophene, a higher concentration of functionalized thiophene units is incorporated into the polymer chains. The measurement of the conductivity on these polymeric films gave a value in the range of 10 -3 to 10 -2 S.cm -1 , which is comparable to that of the unsubstituted polythiophene and consistent with the conjugation grade suggested by electrochemical and UV-vis spectroscopic data. As expected, the pendant reactive ester groups on the electrode surfaces react rapidly with different amino compounds without loss of the electroactivity of the polymers. Therefore, these novel polymeric materials can be used as electrode interfaces for further functionalizations, especially for the immobilization of amines, peptides, and enzymes.

Synthesis and electropolymerization of new p-nitrophenyl-functionalized thiophene derivatives

Electrooxidative polymerization of three new p-nitrophenyl-functionalized thiophene derivatives leads to materials which show the electroactivities of both nitrobenzene and polythiophene. However, other than the reversible redox transition in solution, the nitro groups exhibit a complex nature of the cyclic voltammetric curve in the obtained solid polymeric films. It was found that the electrochemical behavior of the nitro groups has a dramatic effect on the conjugated π-electron systems of the substituted polythiophenes. Upon electrochemical addressing of the nitro groups the electroactivities of the corresponding polymers decrease rapidly compared to their analogous polymers without nitro groups. FTIR studies of these polymers revealed that after the reduction/oxidation process of the nitro groups still a large amount of electrolyte salt remains in the polymer films. As typical of functionalized polythiophenes. however, these new polymers can be switched under controlled conditions between their oxidized and neutral forms and exhibit the typical properties of electroactive polythiophenes, e.g., electrochromism.

Reactive groups on polymer‐coated electrodes, 9. New electroactive polythiophenes with epoxy and cyclic carbonate groups

Two new functionalized thiophene derivatives bearing epoxy and carbonate groups were synthesized. The electrooxidative polymerization of both monomers led to stable electroactive polymers, while the functional groups remained unchanged during the polymerization process. Electrochemical and spectroscopic data of the resulting homopolymers reveal that these polymers possess an extended conjugated π-electron system comparable to unfunctionalized poly(3-alkylthiophene)s. Both monomers can also easily copolymerize with 3-methylthiophene to form the corresponding conducting copolymers. SEM photographs show that the obtained homopolymers and copolymers exhibit a very compact homogeneous morphology, indicating that the new thiophene monomers have good formability of polymer films. The measurement of electrical conductivity of these polymers by means of two-probe method gave values in the range of 10 2 to 10 -1 S . cm -1 . Using butylamine and 2-aminoanthraquinone as model compounds, it was demonstrated that amino compounds easily react with pendant epoxy and cyclic carbonate groups and are convalently attached to the new electroactive polymer surfaces. Thus, a new type of conducting polymers with pendant reactive groups was developed.

Reactive groups on polymer coated electrodes, 12. New conducting carrier materials: polyalkylthiophene functionalized with amino group and its protected forms

The synthesis and electropolymerization of 3-alkylthiophenes functionalized with a terminal amino group and its protected forms are reported. As expected, due to the strong electronic interference of the amino group, the electropolymerization of the unprotected monomer is fully inhibited. After protection of the amino group the polymerizability of the corresponding monomers is considerably improved; however, the successful polymerization process clearly depends on the nature of the used protective group. Only such monomers in which the nucleophilic character of the amino group is strongly suppressed by a suitable proctective group undergo electropolymerization to form the corresponding electroactive polymers. The obtained polymers are electrochemically stable and, besides the typical properties such as redox behavior and electrochromism, they exhibit a distinct solvatochromic behavior. Electrical conductivity measurements on their oxidized forms by means of the two-probe method give values in the range of 10 -3 to 10 -2 S . cm -1 . The feasibility of using the resulting polymers as conducting carrier materials was demonstrated by the removal of the protecting groups and the subsequent attachment of a redox active ferrocene compound. Electrochemical and spectroscopic experiments confirmed that after the polymer analogous reaction the used redox active ferrocene model compound is covalently immobilized onto the polymer surface and the electroactivity of the bonded redox groups as well as the carrier materials is retained.

EPR investigations of β-deuteriated 5,5″-dimethyl-2,2′:5′,2″-terthiophenes

The unambiguous assignment of the β-hyperfine coupling constants of the radical cations of 5,5″-dimethyl-2,2′ : 5′,2″-terthiophene (11) has been achieved by EPR spectroscopic investigations of the deuteriated compounds 12, 13 and 14. The syntheses of these substances were achieved by cross-coupling following the Negishi and Kumada reaction starting from deuteriated derivatives of chloromethylated thiophene derivatives. The generation of the radical cations was carried out by electrochemical oxidation at a constant potential in the EPR spectrometer. In the presence of acidic compounds a D–H exchange at the β-positions of oligothiophenes was observed. The experimentally determined spin density distribution was rationalized by means of semiempirical quantum mechanical calculations (RHF-INDO-SP). Theoretical and experimental assignments are in good agreement.

Flüssig-kristalline Verbindungen aus der Thiophenreihe, Teil 3 Azomethine und Vinylene / Liquid Crystalline Compounds in the Thiophene Series, 3 Azomethines and Vinylenes

A number of azomethines and vinylenes, containing 4,4′-biphenylylen and 2,2′-bithienyl-5,5′-diyl units as mesogenic groups has been synthesized and characterized by their elem ental analyses, IR and 1H NMR spectra and studied in relation to their liquid crystalline properties by DTA analysis and visually by their textures microscoping under polarized light. The described compounds are compared with analogous compounds of the benzene series.

Flüssig-kristalline Verbindungen aus der Thiophenreihe 1. Flüssig-kristalline Thiophencarbonsäureester / Liquid Crystalline Compounds in the Thiophene Series 1. Liquid Crystalline Thiophene Carboxylic Esters

Carboxylic esters have been prepared from 5-alkyl-2-thiophenecarboxylic acid and hydrochinone, biphenol, respectively cholesterol as well as one ester from 2,5-thiophene dicarboxylic acid and p-ethylphenol. Only the esters from biphenol respectively cholesterol have liquid crystalline phases

Liquid Crystalline Compounds in the Thiophene Series, Part 12+ Synthesis and Characterization of Side Chain Polysiloxanes with Low Transition Temperatures

Abstract Polysiloxanes as side chain polymers containing the 2.2′-bithiophene unit, hexyl and octyl terminal groups and spacer units with 3, 5. 6 and 10 methylene groups were prepared and characterized. These polymers have monotropic liquid crystalline phases with transition tem peratures below 0 °C (e. g. for polymer 6p: isotropic → liquid crystalline transition: -20 °C; liquid crystalline → solid transition: -43 °C). Polymers with a trimethylene spacer group must contain an octyl terminal group for forming liquid crystalline phase; a hexyl group does not form such a phase.

Flüssig-kristalline Verbindungen aus der Thiophenreihe, Teil 4. Azomethine und Vinylene mit zentralen Azobenzol-, Stilben- und 1,2-Di(2-thienyl)ethylen-Einheiten / Liquid Crystalline Compounds in the Thiophene Series, Part 4. Azomethines and Vinylenes with Central Azobenzene, Stilbene and 1,2-Di(2-thienyl)ethylene Moieties

Abstract Azomethines and vinylenes, containing azobenzene, stilbene or 1,2-di(2-thienyl)ethylene moieties as central groups with additional thiophene systems has been synthesized and charac-terized by their elemental analyses, IR and 1H NMR spectra and studied in relation to their liquid crystalline properties by DTA analysis and visually by their textures microscoping under polarized light. The liquid crystalline properties of these compounds and some related compounds described in literature are compared and the geometrical elements of their structures are discussed.