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The synthesis and electropolymerisation of a new terthiophene, 1,3-di-2-thienylthieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline, is reported. The compound bears a quinoxaline unit fused to the central thiophene ring via a 1,4-dithiin ring; the latter unit ensures a non-planar structure for the molecule. The corresponding polymer, prepared electrochemically, has been characterized by cyclic voltammetry and UV-vis-NIR spectroelectrochemistry. The material is oxidised within the conjugated chain, but the reduction processes are complex and arise from both the polythiophene and the independent quinoxaline units. The polymer has two distinct colour states—orange in the neutral form and green–blue in the oxidised state. Electrochromic studies on poly(1,3-di-2-thienylthieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline) reveal fast switching speeds that are superior to those of poly(3,4-ethylenedioxythiophene) (PEDOT) and a colouration efficiency of 381 cm2 C−1 at 650 nm.

A new series of oligothiophenes bearing electron deficient fluorene units have been prepared and characterised. The materials are functionalised by C8/C11 alkyl chains or triethylene glycol side groups, yet the higher oligomers remain poorly soluble. The absorption characteristics of a sexithiophene analogue (compound 3) have been studied by UV-vis and photoinduced absorption spectroscopy. Photovoltaic cells have been fabricated from blends of 3 and fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photocurrent spectrum of the device matches the absorption spectrum of the sexithiophene system which incorporates an intramolecular charge transfer band arising from the 1,3-dithiole-fluorene units. A modest power conversion efficiency of 0.1% was achieved.

A new family of tetrathiafulvalenes has been prepared. The materials exhibit complex redox behaviour related to the electronic influence of the 1,4-dithiin moieties embedded within the framework of the molecules. The X-ray crystal structure of compound 4 reveals an unusual non-planar conformation of the heterocyclic compound, with the TTF fragment adopting a boat conformation. Theoretical calculations, performed at the DFT level (B3P86/6-31G*), confirm the boatlike structure (C2v symmetry) as the most stable conformation for this family of tetrathiafulvalenes. Upon oxidation, electrons are extracted from the whole molecule and the radical cations and dications remain highly distorted from planarity. For the dications, the 1,4-dithiin units present foldings of ∼40° suggesting the possibility of reaching higher oxidation states in agreement with experimental results. For the tetracations, both the TTF nucleus and the 1,4-dithiin units are singly-charged and become planar. The tetracations therefore present fully-planar, π-delocalised structures and are stabilised by the gain of aromaticity of the TTF and 1,4-dithiin electron-donor units.

The polymerisation of a fused 2,5-dibromothieno-TTF derivative has been achieved using Ni(COD)(2) as the catalyst. Whilst higher molecular weight fractions are sparingly soluble, lower weight samples are soluble in common organic solvents. Cyclic voltammetry shows that the polymer undergoes two reversible oxidation processes at +0.71 and +1.10 V (vs. Ag/AgCl), respectively. The optical and electrochemical band gaps have been deduced by electronic absorption spectroscopy and cyclic voltammetry and are in the range 1.75-1.89 eV. Independent conductivity measurements by impedance spectroscopy and four-probe methods give values of 5 x 10(-7) and 7 x 10(-6) S cm(-1) for the neutral polymer. The highest conductivity for the doped material as a thin film (0.1 S cm(-1)) was obtained from a drop cast solution of poly(11)/TCNQ (1 : 2 molar ratio). EPR and UV-vis spectroelectrochemical experiments reveal that both oxidation processes are centred on the TTF unit of the polymer. Chronocoulometric experiments show that almost two electrons per repeat unit are released upon oxidation at +1.3 V.

This paper describes the chemical and electrochemical synthesis of novel copolymers of thiophene and pyridine. Di-iodination of 3-hydroxypyridine 12 followed by O-substitution gave a series of ethers 14b–d and esters/carbamates 15a–d which were reacted with the stannylated bithiophene derivative 17 in a Stille cross-coupling reaction yielding poly (1b–d) and poly (2a–d) respectively. These chemical polymerisation reactions generally resulted in highly insoluble materials which were difficult to characterise. Ethers 14b–d and esters/carbamates 15a–d gave O-substituted 3-hydroxy-2,6-di(2-thienyl)pyridines 1b–d and 2a–d respectively in Stille cross-coupling reactions with the stannylated thiophene 16. Ethers 1b–d underwent electrochemical polymerisation allowing the synthesis of O-alkylated polymers, poly (1b–d), with electrochemical band-gaps of 1.4 to 1.6 eV. In contrast, the esters/carbamates 2a–d could not be electropolymerised.

The synthesis of a new series of sulfur-rich ligands is reported. These compounds, which are related to the dmit(2-) (2-thioxo-1,3-dithiol-4,5-dithiolato) structure, comprise two 2-thioxo-1,3-dithiol-5-thiolato units linked by a bridging unit at the 4-position of the heterocycle via a dithioether spacer unit. Complexation reactions have been carried out on a variety of metal centres; dialkyl tin and gold(I) derivatives have been isolated and fully characterised. The X-ray crystal structure of an octahedral Ni(II) complex, involving two coordinating pyridine molecules, is presented.

The syntheses and electrochemistry of thieno[3',4'r5,6][1,4]dithiino[2,3-b]quinoxaline (9), 2,3-bis(methylsulfanyl)[1,4]dithiino[2,3-b]quinoxaline (16) and 2,3-ethylenedisulfanyl[1,4]dithiino[2,3-b]quinoxaline (17) are reported, together with the X-ray crystal structures of 9, 16 and the charge-transfer complex 9.TCNQ. In the thieno derivative 9, the molecular structure undergoes a significant change from a boat conformer to a planar system, upon oxidation with TCNQ. Theoretical calculations show that oxidation leads to planarisation of the molecular structure due to the aromatisation of the dithiine moiety. The study of the oxidised/reduced species helps to rationalise the electrochemical behaviour observed experimentally.

The novel annelated monomer thieno[3′,4′:5,6][1,4]dithiino[2,3-b]quinoxaline 1 has been electropolymerised on a variety of electrodes, resulting in films which are electroactive in non-aqueous and aqueous solution. The polymer films exhibit a transformation in voltammetric response corresponding to a positive shift in redox potential in the presence of silver cation, the maximum shift being ca. 150 mV in acetonitrile and ca. 400 mV in aqueous LiClO4 solution. Mercury dication demonstrates a similar, but smaller (ca. 130 mV) shift in aqueous solution. Theoretical calculations clearly show the potential of poly(1) as a metal complexation agent. The Ag+ ion coordinates with 1 in two ways: (i) an apical conformation involving the two dithiine sulfurs and (ii) a lateral σ-complex with a contribution from the quinoxaline nitrogens. The Hg2+ ion prefers to coordinate with the sulfur atoms. The calculations performed for the trimer illustrate that the metal ions can be coordinated simultaneously by two repeat units in the polymer chain.

Bis(dithiolene) metal complexes incorporating fused terthiophene units have been prepared; the nickel analogue undergoes electropolymerisation to afford a low bandgap material with very broad absorption characteristics.

The crystal structure of an iodine monobromide adduct of dimethyl 1,3-dithiole-2-thione-4,5-dicarboxylate reveals a layered polymeric network of donor and acceptor molecules linked primarily through S⋯I–Br charge-transfer and hydrogen bonded interactions.

Luminescent lanthanide complexes have been prepared by exploiting the interaction between lanthanide DO3A complexes and chromophore bearing carboxylates or phosphonates. This interaction can be utilised to probe the choice of sensitising chromophore suited to a given lanthanide. Furthermore, ternary complexes obtained from chromophore appended carboxylates dissociate in the presence of phosphate, while those obtained from phosphonates do not.

The title compound has been reacted with I2, IBr and ICl to afford the charge-transfer adducts 4·2I2, 4·IBr and 4·ICl·½I2, respectively. The products have been characterised by Raman and IR spectroscopy and X-ray crystallography. The adducts contain linear S⋯I–X (X = I, Br or Cl) units (174–178°) in which the S⋯I contacts range from 2.534–2.597 A. In 4·2I2 and 4·ICl·½I2, the materials contain additional ‘free’ diiodine units which are held within a matrix of intermolecular contacts, predominantly through non-covalent halogen–halogen and sulfur–halogen interactions. Although the functional groups in the parent molecule (4) are inert at the supramolecular level, the bromomethyl groups in the adducts contribute strong interactions through Br⋯Br, Br⋯I, Br⋯S and Br⋯H close contacts. The structures of the complexes are polymeric in nature, providing interactions in two and three dimensions.

Three new, highly crystalline 2,5-dibromothiophene compounds polymerise on standing in the absence of solvent and catalyst; X-ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, facilitating the coupling of monomers.