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For some time, gene disruptions in Candida albicans have been made with the hisG-URA3-hisG (‘Ura-blaster’) cassette, which can be re-used in successive transformations of a single strain after homologous excision of URA3. However, the hisG repeats are too large for efficient PCR amplification of the entire cassette, so it cannot be used for PCR product-directed gene disruptions. We describe here a gene disruption cassette, URA3-dpl200, with 200 bp flanking repeats that permit efficient PCR amplification. After transformation and integration to produce both arg5::URA3-dpl200 and rim101::URA3-dpl200 alleles, we find that arg5::dpl200 and rim101::dpl200 segregants, respectively, can be obtained. We have used the cassette to create rim101::dpl200/rim101::URA3-dpl200 mutants exclusively through PCR product-directed disruption. Copyright © 2000 John Wiley & Sons, Ltd.

The performance of a new ion-selective membrane electrode as a suitable probe for measuring silver ions in photographic emulsions was compared with traditional silver/silver halide electrodes and silver bars used by Kodak. The ion-selective membrane was assembled using conventional 10−3 mol dm−3 AgNO3 inner filling solutions and silver ion buffered (at 10−7.2 mol dm−3) solutions in an attempt to achieve lower limits of detection. Membrane fouling on the inner side of the membrane (on storage in conditioning solution) was observed for the latter. Although this prevented the use of the electrode in photographic emulsions, the observation is significant as it implies Donnan exclusion failure due to extraction of primary ions. The behaviour of the conventional membrane electrode was similar to that of silver/silver chloride electrodes in both aqueous solutions and photographic emulsion. This showed that a suitable membrane ion-selective electrode is eminently suitable for the direct measurement of silver ions in photographic emulsion media.

A range of acyclic compounds based on 1,3-dithiole-2-thione-4,5-dithiolate (DMIT), functionalised with a silver binding chain and an alkyl chain, were synthesised and assessed as silver ionophores suitable for incorporation into potentiometric ion-selective electrodes as sensors for silver ions in photographic emulsions. The new ionophores were compared with a commercially available ionophore and a 14-crown-4-based ionophore. The membrane compositions were optimised for silver ion selectivity over a range of ions of relevance in the photographic process. 4-(Butylsulfanyl)-5-(phenylmethylthioethylsulfanyl)-1,3-dithiole-2-one was shown to be the most suitable ionophore in plasticised membrane electrodes, with a Nernstian response in the range 10−1–10−6 mol dm−3 and selectivity coefficients of the order of log KPOTAg/M ≤ −4.0.

Not only a component of molecular conductors! Tetrathiafulvalene (TTF) and its derivatives are versatile building blocks in many areas of materials chemistry. This article reviews the current role of substituted TTFs in cation sensors, liquid crystals, intramolecular charge-transfer and nonlinear optical materials, supramolecular switches and devices, and redox polymers (main-chain, side-chain and dendritic systems).

A series of bi(tetrathiafulvalenyl) derivatives has been prepared from iodo-TTF precursors by Ullmann coupling (copper in refluxing N,N-dimethylformamide) or by reaction with copper(I) thiophene-2-carboxylate (CuTC) in 1-methylpyrrolidin-2-one at 20 °C. Solution electrochemical and UV-VIS spectroscopic studies suggest that there is no significant through-bond interaction between the two TTF units in these systems. The X-ray crystal structures are reported for 4,5,5′,5′′,4′′′,5′′′-hexakis(methylsulfanyl)-4′,4′′-bitetrathiafulvalene 9 and a semiconducting 1∶1 perchlorate salt of 4,5:4′′′,5′′′-bis(ethylenedithio)-5′,5′′-dimethyl-4′,4′′-bitetrathiafulvalene 8+··ClO4−. The torsion angle around the central bond is 89° in 9 and 77° in 8+··ClO4−. The crystal packing of 8+··ClO4− is characterised by puckered layers, parallel to the (001) plane, of cations contacting via their sulfur atoms; the anions occupy infinite channels, parallel to the z-axis and running through the cation motif.

The cyclic voltammetry of a series of soluble N-methylfulleropyrrolidinium salts shows that these materials are better electron-acceptors than unmodified C60. The stability of mono-reduced, zwitterionic, and doubly-reduced anionic species, produced either electrochemically or chemically, has been checked by absorption spectroscopy. Langmuir–Blodgett (LB) layers of the C60 derivatives mixed with tricosanoic acid have been built up on different substrates. The optical properties of the films have been characterized using absorption spectroscopy and their structure was investigated by X-ray diffraction.

The synthesis of new derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene has been achieved by two different routes. Deprotonation of 8 using LDA in THF at −78 °C, followed by in situ quenching of the lithiated intermediate 9 with N,N-dimethylformamide, N-methyl isothiocyanate and methyl chloroformate gave aldehyde, thioamide and methyl ester derivatives 10-12, respectively. Sulfur insertion into the lithiated species 9 followed by reaction of the transient thiolate anion with benzoyl chloride gave the thioester derivative 13 which served as a convenient shelf-stable precursor of other mono-functionalised derivatives of 8. Debenzoylation of 13 and trapping of the transient thiolate anion with iodomethane and 6-bromohexan-1-ol yielded 14 and 15, respectively. Reaction of cation salt 17 with the anion of anthrone 18 gave compound 20, the thiolate anion of which reacted with 6-bromohexan-1-ol to afford the alcohol derivative 21. Subsequent reactions gave alcohol derivative 25 of the title system. The unexpected product 29 was obtained from reaction of 28 with triethyl phosphite. The X-ray crystal structures of compounds 12, 14, 28, and 29 are reported. The molecules adopt a saddle-like conformation; the bis(1,3-dithiole)benzoquinone system is U-shaped through an ‘accumulating bend’ comprising the boat conformation of the central (quinonoid) ring, folding of both 1,3-dithiole rings along S···S vectors, and out-of-plane tilting of the exocyclic CC bonds, all in the same (inward) direction.

The syntheses, electronic, optical and structural properties of a range of derivatives of 9,10-anthracenediylidene are described. The ®rst family of compounds are p-electron donors based on 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene. Recent synthetic developments are reviewed, including the functionalisation, via lithiation and subsequent in situ quenching with electrophiles, of the trimethyl derivative 8. X-Ray crystal structures of selected derivatives reveal that the molecules adopt a saddle-shaped conformation. The second family of compounds are novel single-component donor±p-acceptor species which possess intramolecular charge transfer, notably 10-(4,5-dimethyl-1,3-dithiol-2-ylidene)-9-(2,2dicyanomethylene)anthracene 19. Cyclic voltammetric data, UV/visible spectra, ultrafast time-resolved spectroscopy and X-ray structural data are reported.

The title compound was prepared by reacting the anion of malononitrile with the corresponding ethanal, and characterised by UV–vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography. Attachment of an additional ferrocenyl donor group to the π-donor–π-acceptor system does not enhance intramolecular charge transfer, because its bulk distorts the planarity of the conjugated chain.

The synthesis and physical properties of four series of novel fluorene push−pull compounds (4−7) of the D−π−A type with intramolecular charge transfer (from 1,3- and 1,2-dithiole and 1,3-selenathiole donor (D) moieties) are described. The nature of the heteroatom (S or Se) in the donor fragment has no effect on the maxima of intramolecular absorption bands (λICT), whereas a change of position of the heteroatoms in the dithiole moiety from 1,3 to 1,2 leads to a substantial bathochromic shift in λICT. Solvatochromism, thermochromism, and negative halochromism in these compounds are demonstrated. Cyclic voltammograms of 4−7 exhibit two, separate, single-electron reversible redox waves, the potentials of which (as well as the ICT energies in the molecules) are quantitatively described by σp- constants of the substituents in the fluorene ring. Compounds 4−7 exhibit reversible salt formation in sulfuric acid, and for compound 5g in diluted sulfuric acid an additional absorption in the near-IR region has been ob...

The synthesis is described of a series of mono-, bis-, and tris(1,3-dithiol-2-ylidene) derivatives7,9 and10 starting from 1,3-indanedione. Cyclic voltammetric data establish that the π-electron donor ability of these molecules increases in the sequence7 Mono-, bis-, and tris(1,3-dithiol-2-ylidene) derivatives of 1,3-indanedione have been synthesised, and their π-electron donor ability studied by cyclic voltammetry. The crystal structure of a complex (7a)2·TCNQ is reported. Download : Download full-size image

The focus of this paper is the chemistry of 2-piperazinones and the use of this building block to restrict the conformational freedom of the growth hormone secretagogue NN703 (currently in clinical development). We exploit classical methods for 2-piperazinone synthesis as well as some novel approaches such as a Boronic Mannich reaction. Finally, we report on the ability of the constrained target compounds to release growth hormone in vitro .

Two new synthetic approaches to functionalised derivatives of the 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene system are reported. A range of new derivatives bearing reactive substituents are described.

Guest editors Guillermo Bazan and Martin Bryce introduce thisJournal of Materials Chemistry Cthemed issue on small molecules and monodisperse oligomers for organic electronics.

Syntheses of acenaphtho[1,2-b][1,4]oxathiine 4 and 8,9-bis(methylsulfanyl)acenaphtho[1,2-b][1,4]dithiine 5 are reported. The fairly persistent radical ions of acenaphtho[1,2-b][1,4]dithiine 1, acenaphtho[1,2-b][1,4]benzodithiine 2, acenaphtho[1,2-b]thieno[3,4-e][1,4]dithiine 3, and 4, i.e. 1˙+–4˙+ and 1˙––4˙–, were generated from their neutral precursors and their EPR and ENDOR spectra are reported. Oxidation to the radical cations implies an electron removal from the heteroatoms of the donor dithiine or oxathiine moiety which houses the bulk of the spin population. Accordingly, in the EPR spectra of 1˙+–4˙+, the 1H-hyperfine pattern is only 0.25–0.70 mT wide, while the 33S satellites extend over 2–3 mT. Upon reduction of 1–4 to their radical anions, the extra electron resides in the acenaphthylene π-system. Thus, the EPR spectra of 1˙––4˙– have a total width of ca. 2.2 mT with no observable 33S satellites. The g factors of the radical cations comply with the values for oxidised S-donors, whereas those of the corresponding anions are typical of reduced π-systems without heteroatoms. The crystal structure of 5 is characterised by pseudo-dimers of molecules folded by 54° along the S· · ·S vector of the 1,4-dithiine ring. The structural motif of both 5∶TCNQ and 5∶Br2TCNQ comprises mixed stacks of donor and acceptor moieties. The bond lengths in 5∶TCNQ and 5∶Br2TCNQ show minor perturbation compared with pure 5, which can be attributed to a small degree of charge transfer. The asymmetric unit of 5∶(I7–) comprises one radical cation 5˙+, two I2 molecules and one I3– anion. The radical cation, in contrast with the structures of 5, 5∶TCNQ and 5∶Br2TCNQ, shows only a minor boat-like distortion, and the radical cations form a stepwise stack, parallel to the b axis. Iodine species form an infinite zig-zag chain, running in the general direction of the c axis, i.e. normal to the stacks. The conductivity values of these complexes are low (σrt = ≤ 10–8 S cm–1).

Langmuir–Blodgett films of the title trimethyltetrathiafulvalene derivative 10 have been assembled without the need for added fatty acid: room temperature, in-plane, dc conductivity values of the films before and after doping with iodine vapour were σrt = 10–5 S cm–1 and 10–1 S cm–1, respectively. Over the temperature range 300–100 K the films exhibited a linear current versus voltage relationship, with an activation energy for conductivity Ea = 0.11 eV. Cyclic voltammetric data were obtained for LB films of 10 and the best response was recorded for a 2-layer film; electroactivity gradually disappeared after a few cycles, which is consistent with film desorption from the electrode. UV–vis and IR spectra of the LB films are consistent with a conjugative intramolecular charge-transfer interaction between the triMe-TTF (donor) and ester (acceptor) moieties of 10 (see structure 10′). This increases the amphiphilic nature of 10 and is believed to play an important role in stabilising the LB film structure. Iodine doping of the LB films leads to the formation of radical cations 10·+, and polarised spectra show that the molecules are aligned at a high angle to the substrate surface. Simultaneous electrochemistry and EPR (SEEPR) studies provide insight into the electronic structure of the radical cation species 10·+ in solution; the ethoxycarbonyl group strongly polarises the spin density, and these data are supported by ab initio UHF and B3LYP calculations. The single crystal X-ray structure of the complex (10)2·TCNQ (TCNQ = tetracyano-p-quinodimethane) reveals a mixed ⋯ADDADD⋯ stacking motif with a low degree of charge transfer between the D and A moieties. Analysis of the bond lengths in the donor moiety confirms a contribution from the zwitterionic structure 10′.

This article reviews progress in modifying electrode surfaces with functional organic molecules which act as signalling units upon molecular recognition of a guest molecule or ion. This process triggers a change in the physicochemical properties of the host assembly which can be monitored by an electrochemical response. Topics covered include: molecular recognition in conjugated polymers; molecular recognition in monolayers formed by Langmuir-Blodgett and self assembly techniques; incorporation of recognition sites (‘molecular gates’) in otherwise passivating monolayers; ion channel sensors. Representative redox moieties include: polythiophene and polypyrrole derivatives, paraquat, ferrocene, tetrathiafulvalene, metalloporphyrins, C 60 , Ru(NH 3 ) 6 3+ and Fe(bpy) 2 (CN) 2 0 . Issues relevant to the development of practical, commercially-viable sensors are considered.

The reaction of transient 1,3-dithiole-2,4,5-trithione 4 with acenaphthylene afforded the Diels-Alder adduct 5, which was dehydrogenated to yield 6; cross-coupling of 6 with 7 gave the tetrathiafulvalene (TTF) derivative 8, which was converted into the di(methylsulfanyl) analogue 10, the solution electrochemistry and X-ray crystal structure of which are reported.

Although tetrathiafulvalene (TTF) and its derivatives have been extensively studied for more than 25 years as π-electron donors in intermolecular charge-transfer materials, the intriguing potential of TTF as a donor in an intramolecular sense has only recently been developed. Many versatile, functionalized TTF building blocks are now readily available, and this article will review a range of compounds in which TTF is covalently linked to an electron acceptor moiety by a variety of linking units, sometimes giving rise to an intramolecular charge-transfer (ICT) interaction, which is most frequently manifested in the optical and electrochemical properties. In this context, acceptor subunits include: tetracyano-p-quinodimethane, quinones, electron-deficient aryl groups, pyridinium and bipyridinium units, fullerenes, phthalocyanines, and mesomerically conjugated carbonyl, thiocarbonyl, ester, and related groups. This work paves the way for more systematic and detailed studies of TTF–spacer–A molecules (where A is an acceptor) in which there is increased control of the structural, electronic, optical, and magnetic properties arising from ICT interactions in the ground state, or in the excited state.

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.

Thin films of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), dimethyl- and trimethyl-TTF have been prepared using the thermal evaporation technique. The films were investigated using electron/optical microscopy, optical absorption spectroscopy and d.c. electrical measurements. A maximum in-plane, d.c. room temperature conductivity of 1.6±0.6 S cm−1 was noted for iodine-doped films of BEDT-TTF. The thermal activation energy, over the range 77–300 K, was 0.028±0.02 eV for this material.

The synthesis is described of a series of conjugated donor-π-acceptor molecules where 1,3-diselenoles are the electron donor moieties and dicyanomethylene or N-cyanoimine groups function as the acceptor moieties. Alkenes and aryl groups act as the conjugated spacers. The UV-VIS absorption spectra of these molecules in solution possess a low energy band resulting from intramolecular charge transfer; the wavelength of this band varies significantly with the structure of the spacer group. The solution redox properties, studied by cyclic voltammetry, reveal a reversible one-electron oxidation wave, attributed to the formation of the radical cation of the 1,3-diselenol-2-ylidene moiety, and an irreversible one-electron reduction to form the radical anion located on the dicyanomethylene or N-cyanoimine groups. The X-ray crystal structure of 9 9-(1,1-dicyanomethylene)-10-(4,5-dimethyl-1,3-diselenol-2-ylidene)-9,10-dihydroanthracene 14 is reported. The molecule is strained and adopts a “butterfly conformation” in the ground state due to unfavourable peri-interactions between the 1,3-diselenole selenium atoms and the peri hydrogens.

The synthesis and physical properties of a series of novel fluorene π-electron acceptors (7−9) are described. Cyclic voltammograms of 7 and 8 exhibit three separate reversible (or quasi-reversible) one-electron redox waves, characteristic of strong electron acceptors. Spectroelectrochemical experiments show the appearance in the long-wavelength visible region of absorption bands at appropriate potentials which were attributed to the transformations A → A•- and A•- → A2-. Charge-transfer complexation with N-propylcarbazole in dioxane shows the formation of 1:1 complexes with parameters characteristic for other fluorene acceptors. The single-crystal X-ray structures of 1:1 charge-transfer complexes of tetrathiafulvalene with the electron acceptor 8 and with the strongest fluorene acceptor 1f both show ··A···D···A···D·· stacking in the crystal.

New 1,3-dithiol-2-ylidene derivatives, notably π-extended systems, have been synthesised by Wittig reactions of phosphorane and phosphonate ester derivatives of 1,3-dithiole with activated ketones and α,β-unsaturated ketones. Nitrosation reactions of a range of these π-extended systems, results in the formation of nitroalkenes, via unstable nitrosoalkene intermediates, which, in general, could not be isolated. The X-ray crystal structure of 1-(4,5-dicarbomethoxy-1,3-dithiol-2-ylidene)-1-cyano-1-phenyl-methane reveals a small degree of intramolecular electron transfer from the dithiole ring to the conjugated cyano group.

The functionalisation of tetrathiafulvalene with thiophene units is reported via the synthesis of two multiredox compounds 4 and 5. The two molecules represent a fused structure (4) and a TTF-thiophene system directly linked by a single bond (5); both compounds are endowed with ' 2,5-positions within the thiophene ring, making them accessible to polymerisation reactions. The solution electrochemistry of 4 and 5 reveals the redox properties of the two components: a three-stage oxidation process is seen in each case. Charge-transfer complexes have been prepared, using TCNQ or TCNQF4 as the electron acceptor, with conductivities in the range of 104 to 0.22Scm1. Compounds 4 and 5 have been studied by X-ray crystallography; the former exhibits kappa-packing whilst the latter shows a high degree of conjugation between the two donor moieties.

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.

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.

The behaviour of floating layers ofN-octadecylpyridinium–Pd(dmit)2 , complex 1, on the surface of a pure water subphase has been studied using pressure versus area isotherm measurements. Film properties were dependent on the quantity of material spread and the length of time that the layer was aged on the surface of the subphase before compression (spreading time). Area per complex values suggested that a monolayer was formed only if a small amount of material was applied to the subphase and the spreading time was long (several hours). Multilayer Langmuir–Blodgett (LB) films have been deposited onto hydrophilic glass substrates and examined using surface profiling, scanning electron microscopy with energy dispersive X-ray spectroscopy and optical absorption spectroscopy. Observations using electron microscopy showed that films deposited from fresh floating layers contained aggregates that were tens of microns in size. In contrast to previous studies on multilayer films of N-octadecylpyridinium–Ni(dmit)2 complex, the LB films of complex 1 were electrically conductive without any post deposition doping treatment, with room temperature, in-plane conductivity values as high as 0.15±0.10 S cm–1 . In some cases, super-Ohmic current versus voltage characteristics were recorded, which has been attributed to space-charge-limited conductivity. Multilayers transferred from aged floating layers did not exhibit significant bulk conductivity, either in the as-deposited state or after iodine doping, although some samples contained highly conductive crystallites that were several hundred microns in size. The single crystal X-ray structure of the analogous N-dodecylpyridinium–Pd(dmit)2 complex is reported, which provides the first structural study of a [Pd(dmit)2 ]–monoanion. The anions pack in centrosymmetric dimers, with an interplanar spacing of ca. 3.5 A and Pd‥S(5′) contacts of 3.57 A, which are separated by N-dodecylpyridinium cations (with a Pd‥N contact of 3.83 A).

We report the use of functionalised electron acceptor tetracyanoanthraquinodimethane (TCNAQ) units in the synthesis of novel diad D–σ-A compounds 6 and 7 [D=tetrathiafulvalenyl (TTF) and ferrocenyl] and the triad TTF–σ-TCNAQ–σ-TTF assembly 8. Compounds 6–8 display a very weak, broad, low-energy intramolecular charge-transfer band in the UV–VIS spectra. Nanosecond laser flash photolysis of compound 6 did not lead to any new transient absorptions in the 300–800 nm region, suggesting that if a charge-separated species is formed upon excitation, then back electron transfer occurs very rapidly to regenerate the ground state. Cyclic voltammetry of compounds 6–8 shows that reversible oxidation processes occur for the TTF and ferrocene moieties, and a reversible two-electron reduction occurs for the TCNAQ moiety. Spectroelectrochemical studies on compound 6 have enabled the redox processes to be assigned to the sequential formation of the TTF radical cation and dication upon oxidation, and the TCNAQ dianion upon reduction. Simultaneous electrochemistry and EPR (SEEPR) experiments provide further evidence for intramolecular interaction between the TTF and TCNAQ moieties in compound 6. Quantum mechanical calculations on compound 6, performed by the AM1 method, predict that in its minimum energy conformation the TTF and TCNAQ moieties are approximately orthogonal to one another, with the TCNAQ unit folded into a butterfly conformation.

Recent developments in the functionalisation of tetrathiafulvalene (TTF) have enabled TTF units to be covalently linked into macromolecular systems. Convergent syntheses of dendrimers containing TTF units are presented, including a (TTF)13 system in which TTF units are emplaced at all layers of the structural hierarchy. Thin layer cyclic voltammetry has established that the redox activity of TTF is retained in these macromolecules: sequential oxidation to the radical cation and dication occurs for all the TTF units, yielding highly-charged species in solution. Macromolecules comprising four and eight TTF units built around a phthalocyanine core are also described. These materials present novel architectures with the key property of multi-electron redox activity.

New donor-π-acceptor chromophores 5a-c, 7a-c, 8a-c, 13a-c and 14b-c have been synthesised: substituted 1,3-dithiole derivatives span a range of donor abilities [viz. 4,5-dimethyl > 4,5-bis(methylsulfanyl) > 4,5-bis(methoxycarbonyl)], a conjugated ethylenic or oligoethylenic linker varies the central π-electron unit (one, two and four conjugated double bonds) and dicyanomethylene and N-cyanoimine groups are the acceptor units. Extended tetrathiafulvalene derivatives 15a-c have also been synthesised. The electronic absorption spectra of compounds 5, 7, 8 and 14 reveal a broad low-energy intramolecular charge-transfer band [λ max (MeCN) 354-533 nm] which shifts bathochromically with increasing donor strength of the dithiole ring, and with increasing length of the conjugative pathway. The solution redox properties of 5, 7, 8 and 14, studied by cyclic voltammetry, reveal a reversible one-electron oxidation wave, attributed to the formation of the radical cation of the 1,3-dithiol-2-ylidene moiety, and an irreversible one-electron reduction to form the radical anion located on the dicyanomethylene or N-cyanoimine groups. For the bis(dithiole) donors 15a-c a single two-electron redox wave is observed. The non-linear optical (NLO) properties of 7a-c and 14b have been determined using the EFISH technique: moderate NLO properties are observed for compounds 7a-c [μ.β(0) 85 112 x 10 -48 esu] whereas for the more extensively conjugated compound 14b, the value is increased to μ.β(0) 1170 x 10 -48 esu. The molecular structure and electronic properties of the unsubstituted (R = H ) compounds 7, 8, 14 and 15 have been calculated within the density functional theory approach. The minimum energy conformation corresponds to the trans orientation of the side chain for 7, and the cis orientation for 8, in agreement with X-ray crystal structures and solution NMR data. The redox properties and electronic spectra are discussed on the basis of molecular orbital energies and topologies. The X-ray crystal structures of compounds 7b, 8b and 15b are reported. In 7b the 1,3-dithiol-2-ylidene and dicyanopropene systems are planar and form an angle of 3 c between each other; the 'butadiene' unit has a trans configuration. Molecule 8b is planar (with the exception of the methyl groups) and the imine nitrogen atom is in a syn orientation towards the dithiole group, forming a short intramolecular S... N contact [2.719(6) A]. For both 7b and 8b π-delocalisation is observed within the central conjugated spacer unit. Molecule 15b has a predominantly planar structure, with the central tetraene unit in an all-trans configuration.

To identify families of stable planar anchor groups for use in single molecule electronics, we report detailed results for the binding energies of two families of anthracene and pyrene derivatives adsorbed onto graphene. We find that all the selected derivatives functionalized with either electron donating or electron accepting substituents bind more strongly to graphene than the parent non-functionalized anthracene or pyrene. The binding energy is sensitive to the detailed atomic alignment of substituent groups over the graphene substrate leading to larger than expected binding energies for -OH and -CN derivatives. Furthermore, the ordering of the binding energies within the anthracene and pyrene series does not simply follow the electron affinities of the substituents. Energy barriers to rotation or displacement on the graphene surface are much lower than binding energies for adsorption and therefore at room temperature, although the molecules are bound to the graphene, they are almost free to move along the graphene surface. Binding energies can be increased by incorporating electrically inert side chains and are sensitive to the conformation of such chains.

We explore both experimentally and theoretically the conductance and packing of molecular junctions based on oligo(phenyleneethynylene) (OPE) diamine wires, when a series of functional groups are incorporated into the wires. Using the scanning tunnelling microscopy break-junction (STM BJ) technique, we study these compounds in two environments (air and 1,2,4-trichlorobenzene) and explore different starting molecular concentrations. We show that the electrical conductance of the molecular junctions exhibits variations among different compounds, which are significant at standard concentrations but become unimportant when working at a low enough concentration. This shows that the main effect of the functional groups is to affect the packing of the molecular wires, rather than to modify their electrical properties. Our theoretical calculations consistently predict no significant changes in the conductance of the wires due to the electronic structure of the functional groups, although their ability to hinder ring rotations within the OPE backbone can lead to higher conductances at higher packing densities.

Reactions of tetrathiafulvalenyllithium (TTF-Li) with a range of aldehydes and ketones have been explored for the first time, to provide an efficient route to mono-functionalised TTF derivatives of general formulae TTF-CH(OH)R (R = alkyl, phenyl, tetrathiafulvalenyl and ferrocenyl) and TTF-CR(OH)R′ (R = alkyl, phenyl, R′ = alkyl, phenyl, tetrathiafulvalenyl, ferrocenyl, and R-R′ = fluorenyl). Subsequent transformations involving the reactive alcohol group of some of these compounds are reported. The structures of the three title compounds have been established by single-crystal X-ray analysis.

Electrical impedance measurements over the frequency range 10 Hz to 1 MHz are reported for fatty acid Langmuir - Blodgett (LB) films containing an organometallic tetrabutylammonium Ni(dmit) complex. Experiments were undertaken using both in-plane and out-of-plane electrode configurations. In the latter case, a relationship between the AC conductivity and frequency of the form was found, with n = 0.51 for a film containing a 0.31 molar fraction of fatty acid. This n value was found to decrease with an increase in the amount of the charge-transfer compound. For the in-plane AC measurements, the conductance of the sample was dominated by the DC conductivity of the LB film.

The pyrazinoporphyrazine system 13 (metal-free, zinc and copper derivatives) has been synthesised by tetramerisation of 2,3-dicyanopyrazine monomer unit 10. The structure of 13a-c has been established by 1H NMR spectroscopy, UV/Vis spectrophotometry, MALDI-TOF mass spectrometry, cyclic voltammetry and differential pulse voltammetry. The electrochemical redox behaviour of 13a-c is strongly solvent dependent. The expected two-stage oxidation of the tetrathiafulvalene (TTF) units of 13a-c was observed in a range of solvents; in addition, oxidation and reduction of the pyrazinoporphyrazine core of the metal-free derivative 13a was detected in benzonitrile. On excitation of 13 in the Q-band region no fluorescence was observed, which is presumably the consequence of intramolecular charge transfer between the TTF moieties and the excited state of the central porphyrazine. Molecular modelling studies on 13a and 13c are reported. During the course of this work, the novel TTF macrocycles 11 and 20 were synthesised; their X-ray crystal structures reveal severely bent TTF units, the conformations of which are discussed in detail. The X-ray crystal structures of the bis(1,3-dithiole) systems 15 and 18 have also been determined.

The room-temperature DC in-plane electrical conductivity of multilayer Langmuir-Blodgett films of the long-chain tetrathiafulvalene (TTF) derivative octadecanoyl-TTF (ODTTF), mixed with either octadecanoic acid (OA) or pentacosa-10,12-diynoic acid (PA) and doped with iodine, has been measured with a standard two-probe technique. The conductivity was found to depend strongly on the proportion of fatty acid contained in the film, and this behaviour has been compared with that predicted by classical, two-site, two-dimensional (2D) and three-dimensional percolation theory. A percolation threshold corresponding to an ODTTF content of approximately 50% was observed in both cases, in agreement with the value obtained from the 2D model. For films diluted with OA, however, the conductivity transition was smeared out, suggesting a contribution by charge transport perpendicular to the plane of the substrate. Optical microscope studies of these multilayer films have provided further evidence of a two-phase structure.

The two-legged dye, E-N-hexadecyl-2-[2-(4-octadecylaminophenyl)ethenyl]benzothiazolium iodide, adopts a ‘stretched’ rather than a ‘U-shaped’ configuration at the air/water interface and aligns with one of its hydrophobic alkyl groups adjacent to the subphase. Its Langmuir-Blodgett (LB) films are noncentrosymmetric but lack long-range order, with the chromophores having tilt angles relative to the substrate normal of 35 ± 2 ° in the monolayer and 50 ± 5 ° in a 300-layer film. The second-order susceptibility of the monolayer, its thickness and the real and imaginary components of the dielectric permittivity are χzzz(2) = 80 pmV−1 at 1.064 μm and l = 4.89 nm, er = 3.21 and ei = 1.53 at 532 nm (λ2ω). The second-harmonic intensity increases subquadratically with the number of LB layers, saturating after ca. 100 layers, the susceptibility decreasing with increasing film thickness.

The syntheses of novel ferrocene-based chiral oxazolines 17, 18 and 26 are reported. The application of these compounds as catalysts for asymmetric palladium-catalysed allylic substitution reactions has been investigated. These reactions afford the substitution products in both high yield and high enantiomeric excess. The solution electrochemical redox-behaviour of 17, 18 and 26 in the presence of palladium ions establishes that palladium coordination to the oxazoline results in a significant anodic shift in the redox potential of the ferrocene ligand. The X-ray crystal structure of the ferrocene-hydroxy amide derivative 16 is also reported.

Metal-free phthalocyanine derivatives 2 and 14 bearing eight and four peripheral tetrathiafulvalene (TTF) units, respectively, have been synthesised, and their solution electrochemistry and optical spectroscopy have been studied. The compounds display redox properties arising from the TTF and from the phthalocyanine groups. 1H NMR and UV–VIS spectroscopic studies in solution show that aggregation is strongly solvent dependent. Quenching of the fluorescence of the phthalocyanine core by the TTF units was observed. The X-ray crystal structure of 4,5-bis(hexylthio)-4′,5′-bis(hydroxymethyl)-TTF 11, which was synthesised during the course of this work, has been determined. The hydroxy groups of 11 engage in intermolecular (and interstack) hydrogen bonds. Computer modelling studies on phthalocyanine derivatives 2 and 14 are reported.

A new synthetic approach to tetrathiafulvalene (TTF) dendrimers is reported. Tetrakis(4-chloromethylbenzylthio)tetrathiafulvalene7 is a functionalised core unit which reacts with four equivalents of the thiolate ion generated from compound 16 to afford the trisdeca-TTF derivative 3. Compound 3 is a shelf-stable solid which has been characterised by elemental analysis, MALDI-TOF mass spectrometry, 1 H NMR spectroscopy and solution electrochemistry. Thin layer cyclic voltammetry studies on pentakis-TTF and trisdeca-TTF derivatives 11 and 3 in dichloromethane solution in the presence of 2,3-dichloronaphthoquinone as an internal reference, show that all the TTF units undergo two single-electron oxidations. The single crystal X-ray structure of compound 7 is reported: the molecules have crystallographic C i symmetry and form chair-like stacks parallel to the crystallographic y axis.

Ethylenedithiotetrathiafulvalene (EDT–TTF) derivatives1–4 functionalised with a single aromatic ring have been synthesised and their Langmuir–Blodgett (LB) films have been assembled utilising only 25% molar ratio of fatty acid. For compounds 1, 3 and 4, predominantly Y-type deposition onto solid supports was observed with a transfer ratio close to unity. After doping with iodine vapour, the maximum in-plane conductivity values obtained were σ rt =10 -3 S cm -1 for 1 and 3, and 10 -5 S cm -1 for 4. LB deposition of 2 was not uniform and the conductivity value after doping was low. UV–VIS spectra of the LB films reveal the appearance of a charge-transfer (CT) band at λ max =ca. 900 nm for 1 and 4 after iodine doping. A solution of compound 3 exhibited a weak absorption band at ca. 665 nm which is assigned to an intramolecular CT band; the intensity of this band increases on exposure of the solution to light. This band is not observed in LB films of 3, neither as-deposited nor after doping. Molecular orbital calculations indicate that in the minimum energy conformation of 3, the pyridinium moiety is practically orthogonal to the TTF unit and this conformation may be obtained in solution, enabling charge-transfer to occur. A more linear conformation of 3 in the LB films may prevent intramolecular charge-transfer from occurring. Monolayers of 1, 3 and 4 were characterised by cyclic voltammetry which revealed two redox steps consistent with the formation of the EDT–TTF cation radical and dication, respectively.

Efficient syntheses of 2,2′-ethanediylidenebis(4,5-dimethyl-2 H-1,3-diselenole) 14 and the 1,3-dithiole analogue 16 are described. Cyclic voltammetry establishes that they are efficient π-electron donors. The molecular structures of 14 and 16 have been determined by single crystal X-ray analysis: the crystals are isomorphous and the molecules form planar layers parallel to the crystallographic (1 0 2) plane.

The reaction of 5,6-dimethyl-3-(4-bromophenyl)-1,4,2-dithiazine 1b with dimethyl acetylenedicarboxylate (DMAD) at 180 °C in o-dichlorobenzene affords a mixture of thiophene derivative 5 and isothiazole derivative 6: the former probably via the zwitterionic adduct 3 and dithiine derivative 4, neither of which are isolable; the latter by sulfur extrusion from 1b. Reaction of norbornene with 1b affords dithiine derivative 7. Oxidation of 1b with meta-chloroperoxybenzoic acid yields the 1,1-dioxide derivative 8, the X-ray crystal structure of which is reported. The efficient synthesis of 3-aryl-6-methylthio-1,4,2,5-dithiadiazine derivatives 12a–c by ring expansion of 1,4,2-dithiazolium salts 11a–c with an iodine–ammonia reagent is described. Reaction of 12c with DMAD at 180 °C affords the stable dithiine derivative 14, probably via the intermediate 1,4,2-dithiazine 13. Electrochemical oxidation of 12a–c is irreversible, yielding 1,4,2,5-dithiadiazinium cation radicals at potentials [E ox = 1.55–1.73 V (vs. Ag/AgCl)] which are sensitive to the electronic nature of the para-substituent on the aryl ring. The X-ray crystal structure of 12b is reported.