Karl S. Ryder

Strategies towards functionalised electronically conducting organic copolymers

Here we describe the synthesis and electrochemical polymerisation of 2,5-di(2-thienyl)-3-(3-cyanopropyl)pyrrole, 2,5-di(2-thienyl)-3-(3-cyanopropyl)furan, and 3′-(3-cyanopropyl)-2,2′:5′,2″-terthiophene. We report a synthetic methodology to these important conducting polymer precursor compounds that is facile, convenient and flexible. The key precursor to this study is the functionalised diketone 1,4-bis(2-thienyl)-2-(3-cyanopropyl)butane-1,4-dione. This molecule undergoes convenient ring closure to the terthiophene and dithienylpyrrole and dithienylfuran derivatives, all of which are, to our knowledge, new compounds. Importantly, this approach provides a flexible route to a range of heterocyclic polymer precursors because the cyanoalkyl functionality is grafted to the diketone before ring closure. Subsequently the nitrile group provides synthetic utility either by reduction to the amine, or hydrolysis to the carboxylic acid. The new compounds described here undergo electrochemical polymerisation leading to fixed ratio copolymers of functionalised pyrrole, thiophene and furan with thiophene itself. We describe the characterisation of these polymers using FT-IR and X-ray photoelectron spectroscopies.

Pyrrole and polypyrrole-based liquid crystals containing azobenzene mesogenic groups

Here we discuss the thermotropic and electrochemical properties and polymerisation of a series of N-substituted pyrrole monomers bearing mesogenic 4-substituted azobenzene attached as a pendant group via alkyl spacers. We discuss the effect upon these molecular properties of chain length and substitution of the azobenzene moiety with methoxy, cyano and nitro terminal groups. Additionally we present here the first crystal structure determination and analysis of two N-alkylpyrroles bearing mesogenic groups.

Role of conducting polymeric interfaces in promoting biological electron transfer.

In this paper, we explore the role that polymer conductivity and functionality play in determining the nature of molecular recognition at artificial polymer interfaces, as evidenced by electron transfer with the small redox protein, cytochrome c. The relationship is investigated electrochemically using cyclic voltammetry in order to assess the degree of molecular recognition between the biological molecule and carboxyl-functionalized beta-substituted poly(thiophenes) and poly(pyrroles), as well as a co-polymer matrix of these derivatives. In the latter case, the co-polymer film was analysed quantitatively using X-ray photoelectron spectroscopy, and it was found that its composition did not reflect the initial molar ratios of the monomers prior to electrodeposition.

Structure and conductivity in substituted polypyrroles. Part 1. Synthesis and electropolymerization of N‐trimethylsilylethoxymethyl‐3‐methyl‐4‐pyrrole carboxylate ethyl ester

The electrochemical polymerization of N-trimethylsilylethoxymethyl-3-methyl-4-pyrrole carboxylate ethyl ester (MPCE-SEM) in the presence of pyrrole, to give free-standing copolymer films is described. These films have been characterized by surface conductivity measurements, reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Increasing the relative concentration of MPCE-SEM in the polymerization solution resulted in an increase in the proportion of these units in the copolymer film. Increasing the proportion of MPCE-SEM units in the copolymer resulted in a decrease in surface conductivity. This is consistent with expectation because N-substituted polypyrroles tend to have lower conductivity values than unsubstituted polypyrrole. Significantly, it has also been shown that the N-protecting group of the MPCE-SEM unit can be removed after polymerization under mild conditions in a solid phase deprotection procedure.

XPS assaying of electrodeposited copolymer composition to optimise sensor materials

Copolymers prepared by electrodeposition from solutions containing both pyrrole and one of a variety of functionalised pyrroles were prepared. The composition of the copolymers was determined by XPS analysis involving deconvolution of the C(1s) spectrum using the C (1s) spectra for the homopolymers of pyrrole and the appropriate functionalised pyrrole. A constraint in the fitting routine was provided by quantification of the N (1s) signals. In general, addition of a small amount of pyrrole to a deposition solution containing only the functionalised pyrrole monomer resulted in a copolymer with a disproportionately large mole fraction of pyrrole units. For copolymers of pyrrole prepared with different functionalised monomers, the different variations of copolymer composition with deposition solution composition can be accounted for, in part, by the lower reactivity towards polymer deposition of the functionalised pyrrole. An additional influence on copolymer composition may come from different functionalised monomers giving rise to polymer matrices of differing porosity. Matrices with larger void spaces may allow preferential polymerisation of the smaller monomer species (pyrrole). Examples are given illustrating how optimisation of copolymer composition is of advantage in the preparation of modified electrode sensors for use in biosensing and olfactory systems

Strategies towards functionalised electronically conducting organic copolymers: Part 2. Copolymerisation

Here we discuss the application of X-ray photoelectron spectroscopy and absorbance–reflectance FT-IR spectroscopy to establish and quantify reactivity relationships between a range of thiophene and pyrrole monomers. In particular we investigate the application of these techniques to the characterisation of conducting polymer materials grown potentiostatically from solutions containing a binary mixture of monomers. Our data have shown that XPS is especially effective in determining polymer composition and the linear correlation between this and solution composition has enabled prescriptive synthesis of copolymer materials from the different combinations of monomers described here. This technique is much more convenient and more reliable than elemental analysis. In contrast we show that FT-IR studies, whilst providing a useful qualitative guide to the functional group content of the material, do not facilitate detailed quantitative analysis because of large intrinsic errors.

N-Benzyl-2,5-bis(2-thienyl)pyrrole.

The solid-state structure of the title compound, C19H15NS2, is unusual among substituted thiophene/pyrrole derivatives in that the molecular packing is dominated by pi-pi interactions between the benzyl substituents. This may be due to the large torsion angles observed between adjacent heterocycles. Torsion angles between adjacent rings in polypyrrole and polythiophene conducting polymers are related to conjugation length and the conductivity properties of the polymer materials. The title compound crystallizes in space group P21/c with two molecules in the asymmetric unit, both of which exhibit disorder in one of their thiophene rings.

Self-recognition and hydrogen bonding by polycyclic bridgehead monoalcohols

Our interest in the relationship between the hydrogen bonding motifs displayed by monoalcohols and the properties of the solids which contain these motifs has led us to determine the crystal structures of three polycyclic bridgehead monoalcohols. One C10H16O isomer crystallises in the space group P2(1)2(1)2(1) but the three molecules which comprise the asymmetric unit are related approximately by the operations of a 3(1) screw axis. They are linked by hydrogen bonds to form an infinite helix. A second C10H16O isomer forms rings containing four molecules joined by cooperative hydrogen bonds. The chiral space group P4(1)2(1)2 accommodates molecules of the S,S and R,R enantiomers in the molar ratio 92:8 (ee 84%) owing to disorder. A related C9H14O2 keto-alcohol forms infinite chains by C-OH...O = C hydrogen bonding. These hydrogen bond motifs are shown to be typical for 45 tertiary monoalcohols, CmHnOH, present in the Cambridge Structural Database. Tertiary monoalcohols display in a more pronounced form the strong preferences for trigonal and tetragonal space groups and for asymmetric units containing several molecules which are established features of the crystallochemistry of monoalcohols.

Unusual synthesis and crystal structure of 4-tricyclanol

Abstract Here we report the synthesis of 4-tricyclanol, 6 , via an unusual route and its characterisation, by single crystal X-ray diffraction studies. The crystal structure of 6 shows extended hydrophobic channels and catenated hydrogen bonding. Both of these structural features are, to our knowledge, unique in multicyclic cage alcohols. The structures of similar compounds such as 1-adamantanol and cis-verbinol are based on small aggregate hydrogen-bonded clusters. We propose that the catenated hydrogen-bonded structure of the crystal phase of the title compound leads to the unusual morphology of the crystalline sample. Whereas crystals of other multicyclic cage alcohols are typically cuboid in shape, those of 4-tricyclanol, are very long (20–30 mm) needles with flat rectangular cross-sections (1–2×0.3 mm). The long axis of these crystals extends in the direction of the catenated hydrogen bonding.

1,1-bis(phenylsulfonyl)-1-(pyridinio)methanide.

The title disulfonyl-stabilized pyridinium ylide, C(5)H(5)N(+)-C(-)(SO(2)C(6)H(5))(2) or C(18)H(15)NO(4)S(2), contains a near planar NCS(2) core. The structure suggests that the formal negative charge of the ylide C atom is delocalized to the S atoms rather than the N atom. Structural features of pyridinium ylides are briefly discussed.