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The synthesis of a family of alkanethiol molecules with planar aromatic head groups, designed to anchor molecules effectively to graphene electrodes, is reported. Characterisation of self-assembled monolayers of these molecules on a gold surface via conductive atomic force microscopy shows that when an aromatic head group is present, the conductance Ggraphene obtained using a graphene coated probe is higher than the conductance GPt obtained using a platinum (Pt) probe. For Pt probe and graphene probe junctions, the tunnelling decay constant of benzyl ether derivatives with an alkanethiol molecular backbone is determined as 𝛽 = 5.6 nm-1 and 3.5 nm-1, respectively. The conductance ratio Ggraphene/GPt increases as the number of rings present in the aromatic head unit, n, increases. However, as the number of rings increases, the conductance path length increases because the planar head groups lie at an angle to the plane of the electrodes. This means that overall conductance decreases as n increases. Density functional theory-based charge transport calculations support these experimental findings. This study confirms that planar aromatic head groups can function as effective anchoring units for graphene electrodes in large area molecular junctions. However, the results also indicate that the size and geometry of these head groups must be considered in order to produce effective molecular designs.

New cationic mono- and AIE tetra-nuclear Ir(iii) complex-porphyrin conjugates and the corresponding carrier-free NP PSs by self-assembly methods without any auxiliary reagents, [TPP-Ir]+ NPs and [TPP-4Ir]4+ NPs, are obtained for highly efficient PDT.

Photodynamic therapy (PDT) is a promising cancer treatment method. Traditional small-molecule photosensitizers (PSs) suffer from low intersystem crossing (ISC) ability and aggregation-caused quenching (ACQ), which adversely affects the luminous efficiency and singlet oxygen (1O2) yield of PSs in the aggregated state. Ir(III) complexes are promising PSs with long excited-state lifetime, good photophysical and photochemical properties and large Stokes shifts. Aggregation-induced emission (AIE) characteristics could reduce the nonradiative recombination and improve the ISC ability of excited states through the restriction of the intramolecular motions in aggregated states. Accordingly, two AIE-active Ir(III) complexes Ir-1-N+ and Ir-2-N+ were successfully designed and obtained based on Schiff base ligands. Experimental results showed that Ir-1-N+ and Ir-2-N+ have good photophysical properties and the corresponding nanoparticles (NPs) have good water solubility and 1O2 generation ability. Notably, Ir-2-N+ NPs can be efficiently taken up by mouse breast cancer cells (4T1 cells) with good biocompatibility, low dark toxicity and excellent phototoxicity. This work demonstrates a versatile strategy for exploiting efficient transition metal PSs with a cationic ligand in PDT.

The integration of an aggregation induced emission (AIE)-active Ir(III) complex and upconversion nanoparticles (UCNPs) has achieved a NIR-irradiated photosensitizer (PS), UCNPs@Ir-2-N. This PS has satisfactory biocompatibility, excellent phototoxicity, good accumulation in cells and high 1O2 generation ability, thereby effectively killing 4T1 mouse cancer cells in vitro. This work has potential for future photodynamic therapy (PDT) applications.

Purely organic molecules, which emit light by dual emissive (DE) pathways, have received increased attention in the last decade. These materials are now being utilized in practical optoelectronic, sensing and biomedical applications. In order to further extend the application of the DE emitters, it is crucial to gain a fundamental understanding of the links between the molecular structure and the underlying photophysical processes. This review categorizes the types of DE according to the spin multiplicity and time range of the emission, with emphasis on recent experimental advances. The design rules towards novel DE molecular candidates, the most perspective types of DE and possible future applications are outlined. These exciting developments highlight the opportunities for new materials synthesis and pave the way for accelerated future innovation and developments in this area.

Nonconventional chromophores, without classic conjugation and rigid units, are a hot topic of luminescent materials nowadays because of their unique under-explored fundamental properties and their promising applications. Despite the increased attention recently paid to this exciting area, the structural design and the mechanism of photoluminescence in these materials remain unclear and controversial. Different luminescence mechanisms have been successively proposed in recent years, such as oxidation, aggregation of carbonyl units, interactions with phenyl groups, clustering of chromophores and through-space conjugation, etc. This review summarizes oligomers/polymers with unconventional chromophores reported in recent years, which are classified according to their chemical structures and luminescence mechanisms. We present an interconnected overview of the topic highlighting the opportunities for new materials synthesis, looking forward to accelerated future innovation and developments in this area.

Soft luminescent gel materials have many practical applications due to their excellent solution processability, thixotropic, soft and facile coating performance. Here we have prepared a series of oligourethane (OU)-based gelators with fine-tuned optical properties. Chromophores with different π-conjugated lengths were introduced into the backbone in order to systematically control the energy gaps of the OUs. Blue/green/red (BGR) fluorescent gelators were thus achieved. The gelation behavior was driven by non-covalent bonds, notably hydrogen-bonds and van der Waals interactions. Because of the dynamic character of these non-covalent interactions, a simple mixture of sols could revert back to homogeneous hybrid gels. Upon gelation, the extended network of the gels leads to sequential multichromophoric Förster resonance energy transfer (FRET). Benefiting from the presence of three primary colours, the resultant hybrid gel exhibited almost any desired visible emission colour at different ratios of gelators. Of particular significance, a white-light-emitting diode (WLED) was prepared with CIEx,y coordinates (0.35, 0.33) in the hybrid gel formed by precise control over the OUB/OUG/OUR stoichiometry. This type of supramolecular gel holds promise in designing large-area, flexible optical illumination, fluorescent labels and light-harvesting systems, and could be a suitable scaffold for new-generation soft materials with tunable optical properties in display technologies.

Blue-emitting gels are scarce, especially oligomeric/polymeric systems. Here, a series of 4,4′-sulfonyldiphenol (SDP) based oligourethane derivatives (OUs), namely OUHDI, OUHMDI and OUTDI based on 1,6-hexamethylene diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate) and 2,4-diisocyanatotoluene, respectively, were rationally designed and obtained by simple procedures. The new oligomers all display aggregation-induced blue fluorescence and upon gelation they achieve enhanced bright deep-blue emission as a result of interchain hydrogen bonding and oxygen cluster interactions. The OUs show spontaneous thermoreversible gelation in solvents which possess hydrogen-bond receptor units (C[double bond, length as m-dash]O or S[double bond, length as m-dash]O) which facilitate self-assembly of the OU chains into nanotubes. The oligourethane gels (OUGs) possess excellent ability for resisting external stress while at the same time exhibiting a distinct viscous flow state. The results illustrate that heteroatomic non-conjugated oligomers with advantageous hydrogen bonding interactions and oxygen clusters provide an efficient route to photoluminescent blue-emitting gels. The thermoreversible OUGs with excellent mechanical properties have been exploited to make sticky coatings, transparent films and a blue fluorescent molded shape using simple fabrication processes.

The development of metal complexes for optoelectronic applications is a fertile area of research. In contrast to the rigorous development of mononuclear metal complexes, dinuclear species have been less well studied and their fundamental chemistry and applications are under-explored. However, dinuclear species present special properties and functions compared with mononuclear species as a consequence of tuning the bridging ligands, the cyclometalated ligands or the two metal centers. More recently, dinuclear species have enabled important breakthroughs in the fields of OLEDs, photocatalytic water splitting and CO2 reduction, DSPEC, chemosensors, biosensors, PDT, smart materials and so on. Here we present an overview of recent developments of dinuclear metal complexes, their multifunctional properties and their various applications. The relationship between structure and property of dinuclear species and important factors which influence device performance are discussed. Finally, we illustrate some challenges and opportunities for future research into dinuclear metal complexes. This review aims to provide an up-to-date summary and outlook of functional dinuclear metal complexes and to stimulate more researchers to contribute to this exciting interdisciplinary field.

This work shows that trifluoromethyl (CF3) substituents can be used to increase the rate of thermally activated delayed fluorescence (TADF) in conjugated organic molecules by tuning the excitonic character of the singlet and triplet excited states. The synthesis and detailed photophysical characterization of four new functionalized donor–acceptor–donor (D–A–D) compounds using CF3-substituted-thioxanthene-S,S-dioxide and dimethylacridine units are presented. Several compounds are reported to exhibit rapid blue/green thermally activated delayed fluorescence with major delayed fluorescence lifetime components of ≈1–2 μs. Changes in the orbital character of singlet and triplet states (local vs. charge transfer) result in significant changes in rates of delayed fluorescence, despite similar ΔEST values. The change in orbital character is well supported by TD-DFT calculations. Electrochemical measurements reveal strong shifts in redox potentials that can be induced by σ-electron withdrawing CF3 substituents. Trifluoromethyl substituted compounds with a wider ΔEST also perform more efficiently than might be expected due to the demonstrated changes in excited state character. This study reveals important photophysical and molecular design implications for the future development of TADF emitters.

The synthesis is reported of twelve new symmetrical carbazole dimers in which the carbazole units are linked via 1,4-phenylene spacers. There are two distinct series of compounds based on the position on the carbazole ring where the phenylene spacer is attached: this is either at carbazole C(3) (series 1a–1f) or at C(2) (series 2a–2f). The central phenylene ring is substituted with either two methyl, two methoxy or two cyano substituents which impart an intramolecular torsional angle between the phenylene and carbazole rings, thereby limiting the extent of π-conjugation between the carbazole units, and raising the triplet energies of the molecules to ET 2.6–3.0 eV, as determined from their phosphorescence spectra at 80 K. Structure–property relationships were studied by UV-vis and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. A notable observation is that substitution at the 2-position of carbazole (linear conjugation) exerts control over the position of the HOMO, while substitution at the 3-position of carbazole (meta conjugation) allows greater control over the LUMO. X-ray crystal structures are reported for two of the bicarbazoles. Compound 2d is shown to be a suitable host for the sky-blue emitter FIrpic in PhOLEDs, with improved device performance compared to CBP as host.

A series of luminescent non-conjugated polyurethane derivatives (PUs) has been obtained in a facile way in high yields. The polymers show highly selective and sensitive detection of 2,4,6-trinitrophenol (TNP) (picric acid). The selectivity for TNP is accomplished via combination of a strong inner filter effect (IFE), Förster resonance energy transfer (FRET) and photoinduced electron transfer (PET). A convenient indicator paper for the visual detection of TNP has been constructed by immobilization of the polymer PU1 on filter paper. The PU1-coated filter paper presents a rapid detection of TNP in water with a low concentration limit of 10−10 M, ∼0.229 ag cm−2. This is a simple, low-cost and highly efficient method for the detection of TNP.

Correction for ‘Electronic conductance and thermopower of single-molecule junctions of oligo(phenyleneethynylene) derivatives’ by Hervé Dekkiche et al., Nanoscale, 2020, 12, 18908–18917, DOI: 10.1039/D0NR04413J.

A neutral dinuclear Ir(iii) Schiff base complex PIBIP has been synthesized and shown to exhibit both piezochromic luminescence (PCL) and aggregation induced emission (AIE) behaviour. An efficient second-level anti-counterfeit trademark and a data encryption device were fabricated using PIBIP as the active material.

An effective strategy for the molecular design of AIE-ML materials is demonstrated based on tetraphenylethene with formyl substituents., Although bright organic mechanoluminescence (ML) has been observed for a few luminophores with aggregation-induced emission (AIE), details of the positive effect of AIE on ML performance remain unclear and a feasible design principle for AIE-ML compounds has not yet been presented. Herein, an effective strategy for the molecular design of efficient AIE-ML materials is demonstrated, based on tetraphenylethene (TPE) building blocks with formyl substituents, which yield non-centrosymmetric crystal structures with prominent piezoelectric properties for molecular excitation combined with AIE features for intense emission. Following this approach, three AIE-active compounds have been developed and are found to show unique ML characteristics. Furthermore, the results of single crystal X-ray analysis and density functional theory (DFT) calculations suggest that the ML performance would probably be further enhanced by creating molecules with larger dipolar moments and enhanced AIE properties.

Electrochemical polymerization of 3-methylthiophene on highly oriented poly(vinylidene fluoride) (PVDF) film was achieved by cyclic voltammetry to yield well-ordered poly(3-methylthiophene) (P3MT) thin films with anisotropic structural and conductivity properties. The conductivity of P3MT along the direction perpendicular to the chain direction of PVDF, after electrochemical dedoping, is 59 ± 3 S cm−1, while that along the PVDF chain direction is 1.2 ± 0.4 S cm−1. The high conductivity of the P3MT is attributed to the well-ordered structure with its flat-on single crystals as confirmed by electron diffraction and Reflection Absorption Infra-red Spectroscopy (RAIRS). The data are consistent with P3MT chains aligned with π–π stacking perpendicular to the chain direction of the PVDF substrate. Epitaxial electropolymerization is an unusual method of preparing highly ordered thin films of organic semiconductors.

A new series of deep blue/blue emitting co-polymers are reported. Poly(9,9-dihexylfluorene-3,6-diyl and 2,7-diyl-co-2,8-dihexyldibenzothiophene-S,S-dioxide-3,7-diyl) derivatives p(F-S) of varying composition have been synthesised. The effects of two different S derivatives with dialkoxy sidechains, the F : S monomer feed ratio, and meta versus para conjugation with respect to the F units have all been investigated in terms of photophysics and polymer light-emitting diode (PLED) device performance in the architecture ITO/PEDOT:PSS/polymer/TPBi/LiF/Al. The meta polymers poly(9,9-dihexylfluorene-3,6-diyl-co-2,8-di(O-methylenecyclohexyl)dibenzothiophene-S,S-dioxide-3,7-diyl) p(Fm-SOCy) in three different co-monomer ratios, P1–3, give deep blue electroluminescence peaking at 415 nm, with the ratio of 70 : 30 p(Fm : SOCy) producing a maximum external quantum efficiency (EQE) ηext, max 2.7%, whilst the ratio of 85 : 15 gave the highest maximum brightness Lmax of 81 cd m−2, with CIE coordinates (0.17, 0.12) The analogous para series poly(9,9-dihexylfluorene-2,7-diyl-co-2,8-di(O-methylenecyclohexyl)dibenzothiophene-S,S-dioxide-3,7-diyl) p(Fp-SOCy) and poly(9,9-dihexylfluorene-2,7-diyl-co-2,8-dihexyloxydibenzothiophene-S,S-dioxide-3,7-diyl) p(Fp-SO6) in two different ratios, P4–7, produced blue emission peaking at ca. 450 nm. The ratio of 70 : 30 F : S units consistently gave better devices than the corresponding 50 : 50 co-polymers. It was also observed that co-polymers incorporating the bulkier SOCy derivatives gave more efficient and brighter devices, with polymer P5 attaining a remarkable ηext, max 3.2%, 4.4 cd A−1, 3.4 lm W−1 and maximum brightness 2500 cd m−2 with CIE (0.16, 0.18).

This work describes bipolar 2,5-diaryl-1,3,4-oxadiazole–fluorene hybrids which incorporate triphenylamine or carbazole units within the π-electron system, viz. compounds 7, 8, 14 and 16. A related bipolar bis(oxadiazolyl)pyridine system 20 is reported. The syntheses of these five new materials are discussed, along with their optoelectronic absorption and emission properties, and their solution electrochemical redox properties. Anodic electropolymerisation of 20 was observed. Calculations using DFT (density functional theory) establish that they all possess a significantly higher HOMO energy level (by 0.60–1.02 eV) than 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-7) due to the presence of electron-rich amine moieties and increased conjugation lengths, thereby leading to more balanced charge-transport characteristics. Devices were fabricated by spin-coating techniques using the bipolar compounds as the emitters in the simple device architecture ITO:PEDOT-PSS:X:Ca/Al (X = 7, 8, 14, 16 or 20). The turn-on voltages were 2.9, 5.5, 3.6, 4.5 and 3.4 V for the devices incorporating 7, 8, 14, 16 and 20, respectively. The highest external quantum efficiency (EQE) was observed for compound 7: viz. EQE 0.36%; current efficiency 1.00 cd A−1; power efficiency 0.56 lm W−1 at 5.7 V. The EQE of the device fabricated from 8 was considerably lower than for devices using other materials due to low light emission. The EL emission peaked at λmax 430, 487, 487 and 521 nm for 8, 14 and 16, and 7, respectively. For the 20 device λmax = 521 nm and 564 nm. Thus the HOMO–LUMO gap has been modified, allowing the colour of the emitted light to vary from light blue through to green by the systematic chemical modification of the molecular subunits. The high chemical and thermal durability of these materials combined with the simplicity of the device structure and low turn-on voltages offers considerable potential for OLED applications.

We describe the synthesis of 2,5-diaryl-1,3,4-oxadiazole–fluorene hybrid molecules, e.g. 2,7-bis[2-(4-tert-butylphenyl-1,3,4-oxadiazol-5-yl]-9,9-dihexylfluorene 6, 2,7-bis{4-[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]phenyl}-9,9-dihexylfluorene 10, 2,7-bis{4-[2-(4-dodecyloxyphenyl)-1,3,4-oxadiazol-5-yl]phenyl}-9,9-dihexylfluorene 11, 2,7-bis{4-[2-(4-dodecyloxyphenyl)-1,3,4-oxadiazol-5-yl]phenyl}-spirobifluorene 13 and analogue 16, comprising the 9,9-dihexylfluorene or spirobifluorene core units to which are attached aryl- or diaryl-oxadiazole units to provide linearly extended π-conjugated systems. The X-ray crystal structure is reported for compound 11. We have fabricated single-layer organic light-emitting diodes (OLEDs) using blends of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as the emissive material with the electron transport (ET) compounds 6, 10, 11, 13 and 16 added to enhance electron injection. For all the devices studied electroluminescence originates exclusively from the MEH-PPV material. The external quantum efficiencies of the devices increased with increasing concentration of the ET compound up to 95% by weight, and are greatly enhanced (>two orders of magnitude) compared to pure MEH-PPV reference devices. Further improvements have been achieved by adding a layer of PEDOT : PSS and efficiencies reach ca. 0.4% at 30 mA cm−2 for devices in the configuration ITO/PEDOT : PSS/MEH-PPV–13 (5 : 95% by weight)/Al.

A series of 2,5-di(aryleneethynyl)pyrazine derivatives has been synthesised in 23–41% yields by two-fold reaction of 2,5-dibromo-3,6-dimethylpyrazine 3 with ethynylarenes (arene = phenyl, 2-pyridyl, 4-ethylphenyl, 4-chlorophenyl, 4-biphenyl) under standard Sonogashira conditions [CuI, Pd(PPh3)2Cl2, NEt3, THF]. Compound 3 has been converted into 2,5-diethynyl-3,6-dimethylpyrazine, which reacts with 2-iodothiophene to yield 2,5-bis(thien-2-ylethynyl)-3,6-dimethylpyrazine. In the X-ray crystal structure of 2,5-di(phenylethynyl)-3,6-dimethylpyrazine 4 the two phenyl rings are parallel and the pyrazine ring is inclined to their planes by 14.2°. Quantum chemical calculations establish that the HOMO–LUMO gap for 4 (3.56 eV) is lower than that of di(phenylethynyl)benzene 12 (3.72 eV). The nitrogen atoms of 4 serve to localise the HOMO on the central ring’s carbon atoms, resulting in a quinoidal-type population, in contrast to 12. Cyclic voltammetric studies establish that 4 undergoes a reduction to the radical anion at ca. −1.9 V (vs. Ag/Ag+ in MeCN), which is almost reversible at high scan rates (500 mV s−1). The UV-vis absorption and photoluminescence profiles of 4 in cyclohexane are similar to those of 12; the emission for 4 (λmax 379 and 395 nm) is red-shifted compared to 12. Single-layer OLEDs using MEH-PPV as the emissive polymer show significantly enhanced external quantum efficiencies (up to 0.07%) when 20% by weight of 2,5-di(biphenyl-4-ethynyl)-3,6-dimethylpyrazine 8 is added as a dopant: this is ascribed to the enhanced electron-transporting properties of the pyrazine system.

A range of new functionalised 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ) derivatives have been synthesised from the key di(halomethyl) building blocks, 10-[4,5-bis(bromomethyl)-1,3-dithiol-2-ylidene]anthracene-9(10H)-one 10, 10-[4,5-bis(chloromethyl)-1,3-dithiol-2-ylidene]anthracene-9(10H)-one 11 and 9-[4,5-bis(chloromethyl)-1,3-dithiol-2-ylidene]-10-[4,5-bis(hexylsulfanyl)-1,3-dithiol-2-ylidene]-9,10-dihydroanthracene 18. A Diels–Alder strategy comprising trapping of the transient exocyclic diene 19, which is derived from 18, with 1,4-naphthoquinone leads to the aromatised TTFAQ anthraquinone system 21. Horner–Wadsworth–Emmons olefination of 21 with the anion generated from reagent 22 gave the fused bis(TTFAQ) structure 23. Pyrrolo-annelated derivatives 30–34 have been obtained in a sequence of reactions from compound 10. Mono-formylation of the pyrrole ring of 32 and 33 under Vilsmeier conditions gave 35 and 36 which upon reaction with 2,4,5,7-tetranitrofluorene gave the donor–π-acceptor diads 38 and 39. Cyclic voltammetry (CV) in solution for all the TTFAQ derivatives shows the typical quasi-reversible two-electron oxidation wave of the TTFAQ core at potentials which vary slightly depending on the substituents. For example, the value of Eox is raised by the electron withdrawing anthraquinone and tetranitrofluorene units of 21 and 38, respectively. The CV of the conjugated TTFAQ dimer 23 showed two, two-electron oxidation waves corresponding to the sequential formation of 232+ and 234+ (ΔEox = 130 mV) providing evidence for a significant intramolecular electronic interaction, i.e. the dication 232+ acts as a conjugated donor–π-acceptor diad, thereby raising the oxidation potential of its partner TTFAQ unit. Spectroelectrochemical studies on 23 support this explanation. A strong intramolecular charge transfer band at λmax 538 nm is seen in the UV-Vis spectra of the TTFAQ–π-tetranitrofluorene diads 38 and 39. The X-ray crystal structures are reported for compounds 30, 33 and 34. The pyrrolo–TTFAQ moiety adopts a saddle-shape with the central ring of the dihydroanthracene moiety folded along the C(9)...C(10) vector in each case. Significant intermolecular interactions are observed in the structures.

New pyrimidine containing oligo(arylene)s, notably the pyrimidine-fluorene hybrid systems 13-16, have been synthesised by Suzuki cross-coupling methodology. An efficient synthesis of the key reagent 9,9-dihexylfluorene-2,7-diboronic acid 10 from 2,7-dibromo-9,9-dihexylfluorene 9 is reported. Cross-coupling of 10 with two equivalents of 2-bromopyrimidine, 5-bromopyrimidine and 2,5-dibromopyrimidine gave 2,7-bis(2-pyrimidyl)-9,9-dihexylfluorene 13. 2,7-bis(5-pyrimidyl)-9,9-dihexylfluorene 14 and 2,7-bis(5-bromo-2-pyrimidyl)-9,9-dihexylfluorene 15 in 23-34% yields. A further two-fold Suzuki reaction of benzeneboronic acid with compound 15 gave 2,7-bis(5-phenyl-2-pyrimidyl)-9,9-dihexylfluorene 16 (35% yield). Ab initio calculations of the geometries and electronic structures at the Hartree Fock (HF) and density functional theory (DFT) levels of theory are reported for compounds 13, 14 and 16 (with ethyl substituents replacing hexyl) and for their dipyrazinyl and bistetraazenyl analogues, 17, 18, 20 and 21. The heterocyclic nitrogen atoms of 13 and 16 facilitate planarisation of the system, compared to 14, which is in agreement with X-ray structural data obtained for 5-bromo-2-phenylpyrimidine 6, 2,5-diphenylpyrimidine 7 and compound 15. Bistetrazenyl derivative 21 is calculated to be a fully planar system. The cyclic voltammogram (CV) of compound 16 in dichloromethane solution shows a quasi-reversible oxidation wave at E(1/2)0 = +1.36 V (vs. Ag/Ag+). Compound 13 is a poorer donor with an oxidation observed at Epa = +1.50 V which is in good agreement with the difference in the energies of their HOMO orbitals calculated at both HF and DFT levels of theory (0.11-0.12 eV). For compound 14 we were not able to measure an Eox potential which should lie at much more positive potentials. Compounds 15 and 16 are blue emitters in solution, with photoluminescence quantum yields (PLQY) of 25% and 85%, respectively. For thin films of 16 the PLQY is reduced to 21%. An OLED using compound 16 as the emissive layer has been fabricated in the configuration ITO/PEDOT/16/Ca/Al: blue-green light (lambda max 500 nm) most likely emanating primarily from excimer states is emitted at a high turn-on voltage.

We describe the synthesis of three new isomeric 1,3,4-oxadiazole–pyridine hybrids, namely: 2,6-, 3,5- and 2,4-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyridine, (PDPy-2,6, PDPy-3,5 and PDPy-2,4, respectively) and a 1,3,4-oxadiazole–pyrimidine hybrid, namely: 2,5-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyrimidine (PDPmDP). The X-ray crystal structures are reported for PDPy-2,4 and the known phenylene analogue 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-7) as a 1∶1 toluene solvate. The packing motif for molecules of both PDPy-2,4 and OXD-7 is that of discrete layers with the mean planes of all the molecules in the crystals parallel to within 6°. We have fabricated light-emitting diodes (LEDs) using poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) doped with rubrene as the emissive material, with and without a thermally evaporated electron conducting/hole-blocking (ECHB) layer of PDPy-2,6, PDPy-3,5 and PDPy-2,4, PDPmDP and OXD-7, in the device configuration ITO/MEH-PPV(Ru)/ECHB layer/Al. Electroluminescence spectra indicate that light is emitted only from the MEH-PPV layer. The bilayer LEDs are considerably more efficient than single layer devices, e.g. the external quantum efficiences of devices incorporating PDPy-2,6, PDPy-3,5 and OXD-7 are 0.14, 0.04 and 0.06% at 40 mA m−2, respectively, cf. 0.007% for the reference single-layer MEH-PPV(Ru) device. There is no clear correlation between experimental EQE values and the PM3 calculated LUMO levels of the materials.

A range of axially substituted silicon phthalocyanines has been synthesised using various carboxylates as the ligands. 4-tert-Butylbenzoic acid gives rigid, orthogonal axial substituents, whilst a thiophene-containing bis-acetate was conformationally more flexible. Varying the aromatic substituents of phenylacetic acids gave phthalocyanines with altered spectroscopic properties, and changes in the alkyl chain length between the phthalocyanine and the aromatic nucleus of the ligand induced variations in the fluorescence lifetime and quantum yield. Three X-ray crystal structures of axially substituted silicon phthalocyanine bis-esters have been determined.

The incorporation of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene units into dendritic structures has been achieved by convergent routes. The key starting material is the 4-(hydroxymethyl) derivative 3. The branches contain aryl ester and aryl ether groups and the core reagent is benzene-1,3,5-tricarbonyl chloride. Dendrimers 10, 15 and 18 with 6 and 12 redox units at the periphery have been characterised by 1H NMR spectroscopy, elemental analysis, mass spectrometry, UV-vis spectroscopy and solution electrochemistry. The 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene redox chemistry is retained in the dendrimer structures: clean formation of hexa(dication) and dodeca(dication) species is observed upon electrochemical oxidation. These highly-charged species enjoy remarkable electrochemical stability as their reduction to the neutral species is thwarted by the loss of aromaticity and the marked conformational change which accompanies this process. Molecular modelling studies were performed on 10, 1012+, 18 and 1824+ by molecular mechanics.

Two novel polynitrofluorene acceptors π-extended with 5-nitrofuran and 5-nitrothiophene moieties (2 and 3), have been synthesised. Cyclic voltammetry experiments show single electron reduction peaks at ca. −0.66–0.67 V (vs. Fc/Fc+); however, this process (probably due to substantial changes in geometry of reduced species) is electrochemically irreversible and re-oxidation of the derived radical anions is observed at +0.05 and −0.04 V, for 2 and 3, respectively. Electronic absorption spectroscopy confirms charge transfer complexation of the studied acceptor with 4,5-dimethyltetrathiafulvalene (Me2TTF) in solution. The X-ray crystal structure of the 1 ∶ 1 charge transfer complex (CTC) of acceptor 2 with Me2TTF shows mixed A⋯D⋯A⋯D stacking, and its comparison with the structure of the acceptor itself indicates a neutral ground state of this CTC. Theoretical HF/6-31G(d) calculations for the acceptor 2 and its radical anion and dianion states are in agreement with this conclusion. Intramolecular hydrogen bonding in 2 between the oxygen of the furan ring and C(8)-H hydrogen of the fluorene moiety is observed in both solution (1H NMR) and solid state (X-ray) and also supported by theoretical calculations

Efficient syntheses are reported for tetraiodotetrathiafulvalene 2, 4-iodo-5-methyl-4′,5′-bis(methylsulfanyl)TTF 3, and 4-iodo-4′,5′-bis(methylsulfanyl)TTF 4 by iodination, using perfluorohexyl iodide, of lithiated derivatives of the corresponding TTF system. Bromination and chlorination of lithiotrimethylTTF using 1,2-dibromotetrafluoroethane and hexachloroethane gave 4-bromo- and 4-chloro-4′,5,5′-trimethylTTF 6 and 7, respectively. Phosphite-induced self-coupling or cross-coupling reactions of 4-iodo-1,3-dithiole-2-thione or 4,5-diiodo-1,3-dithiole-2-thione(one) half-units resulted in TTF derivatives with partial loss of the iodine substituent(s). 4,5-Dibromo-4′,5′-bis(cyanoethylsulfanyl)TTF 15 was prepared by cross-coupling methodology, and converted into 4,5-dibromo-4′,5′-bis(methylsulfanyl)TTF 16 by reaction with caesium hydroxide and then methyl iodide. EPR data are reported for the electrochemically generated cation radicals of trimethylTTFX derivatives (X = I, Br and Cl) 5–7, respectively. For the neutral donors, the X-ray crystal structures are reported for 2, 5, 6, tetramethylTTF 8 and 15. Structure 2 is characterised by a particularly dense packing with continuous chains of intra-stack I⋯I contacts (4.17–4.19 A). The crystals of 6 and 8 are isomorphous, while the structure of 5 is different. The iodo-substituent in 5 affects the packing in a way the bromo-substituent in 6 does not, due to differences in specific interactions rather than steric demands of I and Br, which are similar. Structure 15 comprises face-to-face dimers with inter-dimer Br⋯Br (3.57 A) and Br⋯S (3.55 A) contacts: a remarkable difference in bond distances between the Br and S-substituted dithiole rings is observed. The 1 ∶ 1 charge-transfer (CT) complexes 3·TCNQ and 4·TCNQ (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, 17) display mixed stair-like stacks of alternating D and A moieties: the overall degree of CT is estimated from bond length analysis to be 0.2 e and 0.3 e, respectively. In 3·TCNQ either position of the disordered iodine atom has one short (inter-stack, but intra-layer) contact with a cyano group (I⋯N distances of 3.14 and 3.18 A). In 4·TCNQ a similar I⋯N contact is much longer (3.35 A). In the structure of 5+·I3−·½I2 the cation radical is disordered; dimeric cation radicals display short intra-dimer contacts (S⋯S 3.38–3.39 A, C⋯C 3.35 A) consistent with electron coupling. Each dimer is surrounded by four I3− anions. The crystal structure of 16+·I3− is comprised of layers with interplanar separations of 3.55 A. Cations of one layer overlap with anions of the next, and the packing can be described as mixed stacks parallel to the a axis. The remarkably high conductivity of this salt for a system of 1 ∶ 1 stoichiometry (σrt = 8 × 10−2 S cm−1) is ascribed to partial charge transfer (the charge on the TTF moiety is estimated as +⅔ from bond length analysis) and a continuous system of short non-bonding contacts.

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.

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 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.

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.

The synthesis of 1,4-dithiafulvene-substituted ferrocene derivatives 7, 11 and 12 by reaction of formyl-, diformyl- and diacetyl-ferrocene, respectively, with the carbanion generated from reagents 4a–c and the ylide prepared from reagent 5 is reported. Upon reaction with HCl–diethyl ether, compounds 7a–c undergo an oxidative dimerisation to yield extended tetrathiafulvalene (TTF) derivatives 8a–c. The solution electrochemistry of compounds 7, 8, 11, 12, 14 and 16 has been studied by cyclic voltammetry. The X-ray crystal structures of compounds 8b and 12a are presented.

The new tetrathiafulvalene derivative1, functionalised with an azobenzene substituent, has been synthesised. Cyclic voltammetric and spectroelectrochemical studies in solution demonstrate the reversible formation of the radical cation of 1. UV–VIS spectroscopy suggests that there is a weak interaction between the TTF and azobenzene moieties in compound 1, and demonstrates that trans–cis isomerisation occurs upon photolysis of the azobenzene substituent. Semi-conducting LB films of 1 have been assembled without the need for added fatty acid: room temperature conductivity values of the films before and after doping with iodine vapour were σrt=10–3–10–5 S cm–1 and 2×10–2–10–3 S cm–1 , respectively. No change in the conductivity of the LB films was observed under irradiation.