Adrian J. Moore

Highly conjugated π-electron donors for organic metals: synthesis and redox chemistry of new 1,3-dithiole and 1,3-selenathiole derivatives

The bis(1,3-dithiolium) dication salts 8a–c have been synthesised in three steps (31–51% overall yields) starting from 1,4-bis(bromomethyl)naphthalene, 9,10-bis(chloromethyl)anthracene and 4,4′-bis(chloromethyl)biphenyl, respectively. The bis(halogenomethyl) compounds 5 were converted into the dipiperidiniumbis(dithiocarboxylate) salts 6, which on alkylation with 3-chlorobutane-2-one yielded bis(dithioesters)7; cyclisation of 7 occurred on treatment with concentrated sulphuric acid to give dication salts 8. Dimethyl 1,3-dithiol-2-ylphosphonate 20, dimethyl 4,5-dimethyl-1,3-dithiol-2-ylphosphonate 21 and dimethyl 1,3-selenathiol-2-ylphosphonate 22 were treated with butyllithium in the presence of a range of carbonyl compounds and quinones, e.g., cyclopentanone, cyclohexanone, benzophenone, acetophenone, benzaldehyde, thioxanthen-9-one, anthraquinone, bianthrone and naphthacene-5,12-quinone to yield Wittig–Horner products, e.g., alkenes 26–34 and the anthracenediylidene derivatives 35, 36, 40–43 and 53. Unsymmetrical derivatives 37–39 were prepared in two steps as follows: anthrone reacted with 2-methylthio-1,3-dithiolium iodides 45 and 46 in pyridine-acetic acid to yield ketones 48 and 49 which were then treated with the Wittig–Horner reagents 23–25. Cyclic voltammetric data for the new tetrathiafulvalene, selenatrithiafulvalene and diselenadithiafulvalene derivatives 35–43and 53, show that these systems undergo two-electron redox behaviour which is observed as a single wave. Complexes of these donors with electron acceptors, e.g. 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), have been obtained, some of which are organic semiconductors.

New vinylogous tetrathiafulvalene (TTF) π-electron donors

Abstract The synthesis and solution electrochemistry of ten new ethanediylidene-2,2′-bis(1,3-dithiole) derivatives (7)–(16) is described; charge-transfer complexes have been obtained with tetracyano- p -quinodimethane (TCNQ).

Functionalised Oligoenes with Unusual Topologies: Synthesis, Electrochemistry and Structural Studies on Redox-Active [3]- and [4]-Dendralenes

New [3]- and [4]-dendralenes bearing electron-donor 1,3-dithiole and ferrocene substituents have been synthesised. Compounds 8, 15 and 17 have been characterised by single-crystal X-ray diffraction. Two of the dithiole rings of 8 are conjugated (dihedral angle 9 degrees), while the third dithiole ring is almost orthogonal to this plane, and hence its pi-electron system is isolated. For the dendralene precursor molecule 15, the substituted cyclopentadienyl ring, two C=C bonds and fused dithiole and dithiine rings comprise an extended pi-conjugated system. In molecule 17 the potential conjugation path C(6)C(3) C(4)C(5)-C5Hs is distorted by an 8 degrees twist around the C(3)-C(4) bond and a 7 degrees twist around the C(5)-C(21) bond, and the delocalisation along the chain is insignificant. Solution electrochemical data demonstrate that the dendralenes are strong pi-electron donors, which give rise to dication, radical trication or tetracation species. Spectroelectrochemical studies on compounds 7 and 10 suggest that the radical species are situated within the linear 1,2-ethylenediylidene moieties and that a conformational change may occur at the dication redox stage. UV/Vis spectroscopic data are consistent with poor cross-conjugation in these systems.

Donor–π‐Acceptor Species Derived from Functionalised 1,3‐Dithiol‐2‐ylidene Anthracene Donor Units Exhibiting Photoinduced Electron Transfer Properties: Spectroscopic, Electrochemical, X‐Ray Crystallographic and Theoretical Studies

Steric interactions between the anthraquinoid core and the 1,3-dithiole and dicyanomethylene groups play a key role in determining the physical properties of system 1. The intramolecular charge transfer properties of this donor–π-acceptor species have been explored and cyclic voltammetric data, X-ray crystal structures and ab initio calculations are also reported.

(N-methylthiocarbamoyl )tetrathiafulvalene derivatives and their radical cations : synthetic and X-ray structural studies

Lithiation of 4,5-bis(methylsulfanyl)-TTF 9, 4,5-(ethylenedisulfanyl)-TTF 10, 4,5-dimethyl-TTF 11 and 4,5,5′-trimethyl-TTF 12 (TTF=tetrathiafulvalene) followed by reaction with methyl isothiocyanate affords the corresponding (N-methylthio-carbamoyl)-TTF derivatives 14–17, respectively, in 54–70% yields. These new TTF derivatives display a broad intramolecular charge-transfer band in their UV–VIS spectra arising from conjugation between the donor TTF ring and the acceptor N-methylthiocarbamoyl moiety. Steric hindrance between the adjacent N-methylthiocarbamoyl and methyl substituents in 17 causes a marked hyposchromic shift in this band (λmax 395 nm) compared to compounds 14–16 (lambda;max 435–467 nm). Consistent with the electron-withdrawing properties of the N-methylthiocarbamoyl substituent, its attachment to the TTF ring raises slightly the oxidation potential of the system. Charge transfer complexes of these donors and (N-methylthiocarbamoyl)-TTF 2 with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and salts with bromide anions are reported, some of which have high room temperature conductivity values. The X-ray crystal structures are presented for 16, 17 and the salts 2·Br, 14·TCNQ and (17)2·20. The structure of 16 comprises orthogonal dimers (kappa packing) while in the structure of 17 individual molecules are orthogonal to each other. There is weak intermolecular hydrogen bonding in both 16 and 17. In the structure of 2·Br, the radical cations 2+· are almost planar and they form an infinite stair-like stack of dimers, with bromide anions situated between the stacks, and linked with the cation by a strong N–H‥Br bond. The structure of 14·TCNQ comprises mixed ‥DDAADD‥ stacks; the N-methylthiocarbamoyl group engages in an interstack N–H‥N bond with a TCNQ anion. Analysis of the bond lengths in the structure suggests that there is partial charge transfer from 14 to TCNQ. In the structure of (17)2·20 molecules form mixed ‥DDADDA‥ stacks and analysis of bond lengths suggests that there is only a small degree of charge transfer from donor to acceptor. The geometries of compounds 2, 14, 16, 17 were optimised using the PM3 semi-empirical method and the results compare favourably with the X-ray structural data.

New functionalized tetrathiafulvalenes: X-ray crystal structures and physico-chemical properties of TTF–C(O)NMe2 and TTF–C(O)–O–C4H9: a joint experimental and theoretical study

The synthesis of the new mono- and di-functionalized tetrathiafulvalene (TTF) derivatives 4, 5 and 12–15 is reported. Compounds 4 and 5 have been studied in detail: their single crystal X-ray structures are reported and theoretical calculations at both semiempirical and ab initio levels have been performed. The TTF moiety in the crystal of 4 is folded, whereas in the crystal of 5 it is essentially planar. In the crystal structure of 4 the molecules related via an inversion centre form close dimers which pack in a severely distorted kappa-arrangement. Molecules of 5 assemble into uniform stacks with TTF moieties overlapping the side chains of adjacent molecules. Calculated geometries are in good agreement with the X-ray data, and the distortion from planarity in the crystal of 4 can be explained by nonbonding interactions between the amide substituent and the TTF rings of adjacent molecules. Evidence for intramolecular charge-transfer from the TTF ring to the electron-withdrawing amide and ester substituents of 4 and 5, respectively, is provided by UV-VIS spectroscopy in solution, analysis of the bond lengths in the crystal structure, and by theoretical calculations.

Crown‐Annelated 9,10‐Bis(1,3‐dithiol‐2‐ylidene)‐9,10‐dihydroanthracene Derivatives as Cation Sensors: Synthesis, X‐ray Crystal Structures, Voltammetric and Spectroscopic Monitoring of Metal Complexation

The synthesis of O4S2-crown annelated derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene using the novel Horner-Wadsworth-Emmons reagent 7 is reported. The bis- and mono-crown systems 9 and 12 function as efficient ligands in the voltammetric and UV/Vis spectroscopic recognition of Na+ and Ag+. Solution electrochemical studies reveal that metal complexation to the crown unit(s) leads to a significant positive shift in the potential of the first, two-electron oxidation wave of 9 and 12 [maximum shift E1ox = 115 mV for 9 in the presence of Ag+ (ca. 10 molar equivalents)]. Considerably smaller shifts (< 30 mV) were observed for complexation of Li+, K+ and Ba2+. UV/Vis spectrophotometric studies of metal binding (Na+ and Ag+) to 9 are consistent with the simultaneous formation of 1:1 and 1:2 complexes. The X-ray crystal structures of compounds 10 and 12-CH2Cl2 are reported. The anthracenediylidene moiety of 12 is U-shaped due to the boat conformation of the central (quinodimethane) ring and folding of both 1,3-dithiole rings, providing an overall saddle conformation. The folding in 10 is reduced as steric crowding is relieved by removal of one of the 1,3-dithiole units.

Aryl ester dendrimers incorporating tetrathiafulvalene units: convergent synthesis, electrochemistry and charge-transfer properties

The convergent synthesis of a range of aryl ester dendrimers with peripheral tetrathiafulvalene (TTF) units is reported.4-(Hydroxymethyl)-TTF and 4,5-(2-hydroxymethylpropane-1,3-diyldithio)-TTF have been used as the starting TTF reagents. The core reagents are benzene-1,3,5-tricarbonyl trichloride, terephthaloyl chloride, biphenyl-4-4′-dicarbonyl chloride and 4,4′-oxybis(benzenecarbonyl chloride). Dendrimers comprising up to 12 TTF units have been characterised by elemental analysis, plasma desorption mass spectrometry,1H NMR spectroscopy and solution electrochemistry. Cyclic voltammetry (CV) and ultra microelectrode CV studies show that the TTF dendrimers display nearly ideal redox behaviour for the TTF system with no significant interaction between the TTF units. Thin layer cyclic voltammetric studies show that all the TTF units of these systems undergo two, single-electron oxidations. The dendrimers form charge-transfer complexes upon reaction with iodine in solution. Intermolecular interactions of the TTF radical cations are observed in the UV–VIS spectra of some of the oxidised derivatives.

A new highly-conjugated TTF analogue: Synthesis, electrochemistry and a conducting TCNQ complex of 9,10-anthracenediylidene-2,2′-bis(4,5-dimethyl-1,3-dithiole)

Abstract The TTF analogue (4) has been isolated as the neutral and the dication species. Cyclic voltammetry of (4) reveals a single, two-electron redox couple. Compound (4) is a promising new electron donor and a complex formed with TCNQ is conducting, σrt = 10−2 S cm−1.

A field effect transistor based on Langmuir-Blodgett films of an Ni(dmit)2 charge transfer complex

Abstract Multilayer structures of the charge transfer complex (N-octadecylpyridinium)-Ni(dmit)2 have been deposited by the Langmuir-Blodgett technique onto substrates of gold-coated glass and silicon with a thermally grown overlayer of silicon dioxide. Capacitance measurements have revealed values of relative permittivity of 3.2 and 6.3 for the dmit layers in the as-deposited state and after iodine doping respectively. Thin film transistor structures have been built up incorporating the dmit complex as the semiconducting layer. Modulation and saturation of a current flowing between source and drain by a voltage applied to the gate has been observed. The mobilities of the charge carriers in the dmit layers have been calculated as 2.4×10−5 cm2 V−1 in the as-deposited state and 1.8×10−1 cm V−1 s−1 after doping with iodine.