Search

A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field-effect transistors (OFETs). X-ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.

A new organic semiconductor based on a benzobisthiazole core has been studied as a hole transport material in field effect transistors; remarkably, the material self-assembles in the solid state to give intermolecular short contacts in all three dimensions.

A series of conjugated triaryl compounds have been synthesized, consisting of thiophene or selenophene peripheral units and a central 1,3,4-thiadiazole (TDA) heterocycle. X-ray crystallographic studies on four of the materials reveal that the molecules are planar in the solid state and feature an array of intramolecular (heteroatomic) and intermolecular (heteroatomic and π−π) noncovalent close contacts. Electrochemical oxidative polymerization affords insoluble polymers for EDOT-TDA-EDOT and EDTT-TDA-EDTT. The band gaps of the polymers have been deduced by cyclic voltammetry and electronic absorption spectroscopy and were found to be 1.8−1.9 eV. Both polymers show good stability toward n-doping and the EDTT analogue is more readily reduced than the EDOT-containing system. The enhanced stability toward n-doping, compared with the homopolymers PEDTT and PEDOT, is attributed to the presence of the electron deficient thiadiazole unit. The LUMO of poly(EDTT-TDA-EDTT) is 0.3 eV lower than that of poly(EDOT-TDA-...

We report electrochemical studies, spectroscopy, and electrogenerated chemiluminescence (ECL) of four monodisperse star-shaped truxene core-oligofluorene compounds (T1-T4). All oligomers produced stable radical anions and radical cations and showed blue ECL by ion annihilation with an intensity that could be seen with the naked eye. ECL spectra showed that all ECL emissions were at the same position as the fluorescence emission, except for T1, the compound with the shortest fluorene arms that produced some longer wavelength emission in addition to that seen in the fluorescence spectrum. When tetra-n-butylammonium oxalate was used as a coreactant for T1, the emission was much weaker than that in ion annihilation with the same long-wavelength emission observed, making it unlikely that this emission can be ascribed to excimer formation. The ECL intensity of T4 was about 80% of the common blue ECL emitter, 9,10-diphenylanthracene (DPA), under similar conditions.

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.

The synthesis of five new dihalogen/interhalogen charge transfer adducts featuring cyano and nitro functionalized 1,3-dithiole-2-thiones have been prepared and characterized by x-ray crystallography. The structures feature a complex series of intermolecular close contacts between heteroatoms, as well as hydrogen bonding, to give highly ordered, polymeric assemblies. The adduct 4.IBr crystallizes in a noncentrosymmetric chiral space group and features a stack of molecules assembled through hydrogen bonds. The functional groups of all adducts participate in networks of close contacts, but do not affect the coordination environment of the dihalogen/interhalogen species.

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.

Chirality induction into a uniform, star-shaped fluorene oligomer with a central truxene moiety (T3) was achieved using circularly polarized light in the presence of achiral fluorene or phenanthrene. Induction into T3 alone was difficult, suggesting that close chain packing realized through interactions of T3 with small molecules plays a role in chirality induction.

Current commercial sensors for explosive vapours are high cost bulky equipment not amenable to mass production and thus prevents their mass deployment within society. Our research objective is to create compact sensors that are not only portable but of such low cost that they can be installed in buildings in the same way as smoke detectors. We have developed novel polymers whose properties have been tailored to give them a higher affinity to target nitro group (NO2) bearing molecules associated with explosives. The polymers have been grown electrochemically onto miniature interdigitated electrode platforms yielding miniature sensors. Novel porous polymers based sensors are demonstrated which yield a detection level of 200 ppb of nitro vapours and can be manufactured at low-unit-cost.

This work is part of the TIRAMISU project, funded by the European Commission’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n◦284747 and the Engineering and Physical Sciences Research Council (EPSRC) grants EP/J009016/1 and EP/F059922/1. I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders. The density of organic semiconductor films is an important quantity because it is related to intermolecular spacing which in turn determines the electronic and photophysical properties. We report thin film density and refractive index measurements of polyfluorenes and star-shaped oligofluorene truxene molecules. An ellipsometer and a procedure using a spectrophotometer were used to determine film thickness and mass of spin-coated films, respectively. We present a study of the effect of alkyl side-chain length on the volumetric mass density and refractive index of the materials studied. The density measured for poly(9,9-di-n-octylfluorene) (PF8) was 0.88 ± 0.04 g/cm3 and decreased with longer alkyl side chains. For the truxene molecule with butyl side chains (T3 butyl), we measured a density of 0.90 ± 0.04 g/cm3, which also decreased with increasing side-chain length. Postprint

Novel tetrathiafulvalene (TTF) containing compounds (III) are obtained by four-fold Stille coupling between tetrabromo-dithieno TTF (I) and stannylated thiophene (IIa) or thiazole (IIb).

Two novel tetrathiafulvalene (TTF) containing compounds 1 and 2 have been synthesised via a four-fold Stille coupling between a tetrabromo-dithienoTTF 5 and stannylated thiophene 6 or thiazole 4. The optical and electrochemical properties of compounds 1 and 2 have been measured by UV–vis spectroscopy and cyclic voltammetry and the results compared with density functional theory (DFT) calculations to confirm the observed properties. Organic field effect transistor (OFET) devices fabricated from 1 and 2 demonstrated that the substitution of thiophene units for thiazoles was found to increase the observed charge transport, which is attributed to induced planarity through S–N interactions of adjacent thiazole nitrogen atoms and TTF sulfur atoms and better packing in the bulk.

The authors thank EPSRC for fi nancial support from the UP-VLC project grant (EP/K00042X/1). P.J.S. and I.D.W.S. also acknowledge a Royal Society Wolfson Research Merit Award. Star-shaped organic semiconductors with boron dipyrromethene (BODIPY) cores are color-conversion materials for blue LED-based visible light communications. The difference between 0 and 1 bits is resolved in colour-converted data links at 100 Mb s−1. The BODIPY modulation bandwidth is eight times higher than that measured using conventional phosphor color converters. Publisher PDF

The authors thank EPSRC for financial support from UP-VLC Project Grant (EP/K00042X/1). Visible Light Communications (VLC) is a promising new technology which could offer higher data transmission rates than existing broadband RF/microwave wireless technologies. In this paper, we show that a blend of semiconducting polymers can be used to make a broadband, balanced color converter with a very high modulation bandwidth to replace commercial phosphors in hybrid LEDs for visible light communications. The resulting color converter exploits partial Förster energy transfer in a blend of the highly fluorescent green emitter BBEHP-PPV and orange-red emitting MEH-PPV. We quantify the efficiency of the photoinduced energy transfer from BBEHP-PPV to MEH-PPV, and demonstrate modulation bandwidths (electrical-electrical) of ∼200 MHz, which are 40 times higher than commercially available phosphor LEDs. Furthermore, the VLC data rate achieved with this blend using On-Off Keying (OOK) is many times (∼35) higher than that measured with a commercially available phosphor color converter. Postprint

Nonlinear optical response in organic semiconductors has been an attractive property for many practical applications. For frequency up-converted lasers, to date, conjugated polymers, fluorescent dyes and small organic molecules have been proposed but their performances have been severely limited due to the difficulty in simultaneously achieving strong nonlinear optical response and high performance optical gain. In this work, we show that structurally designed truxene-based star-shaped oligofluorenes exhibit strong structure-property relationships enabling enhanced nonlinear optical response with favorable optical gain performance. As the number of fluorene repeat units in each arm is increased from 3 to 6, these molecules demonstrate a two-photon absorption cross-section as high as 2200 GM, which is comparable to that of linear conjugated polymers. Tailored truxene oligomers with six fluorene units in each arm (T6) show two-photon absorption pumped amplified spontaneous emission with a threshold as low as 2.43 mJ cm-2, which is better than that of the lowest reported threshold in organic semiconductors. Furthermore, we show a frequency up-converted laser using the newly designed and synthesized star-shaped oligomer T6 with a threshold as low as 3.1 mJ cm-2, which is more than an order of magnitude lower than that of any conjugated polymer. Thus, these oligomers with enhanced nonlinear optical properties are highly attractive for bio-integrated applications such as photodynamic therapy and in vivo bio-sensing. © The Royal Society of Chemistry 2015.

The incorporation of 2,1,3-benzothiadiazole units within the arms of a trigonal quarterfluorene–truxene star-shaped system leads to a monodisperse material with stable multi-electron p- and n-doped states and highly efficient yellow electrogenerated chemiluminescence (ECL). The quantum yield for ECL is 7 times greater than that of the common blue ECL emitter 9,10-diphenylanthracene (DPA).

The first synthesis of the selenium analogue of EDOT, together with its electrochemical polymerization and redox and electronic properties of the resulting polymer, poly(3,4-ethylenediselena)thiophene (PEDST), is reported. The HOMO and LUMO values for the polymer (calculated from cyclic voltammetry experiments) are −4.8 and −3.3 eV, respectively, whereas the experimental band gap is 1.55 eV. Within the related series of polymersPEDOT, PEDTT, and PEDSTthe selenium analogue has a significantly lower LUMO value than the oxygen or sulfur derivatives (by ca. 0.55 eV). Quantum chemical calculations on trimers ((EDXT)3, where X = O, S, or Se) show that the most planar conformation within the conjugated chain is achieved by EDOT systems. However, the calculated energy of a fixed planar conformation for PEDST is 13.9 kJ mol-1 lower than the corresponding unconstrained conformer, indicating that a planar structure is preferred; this data corroborates the lower experimental band gap observed for PEDST (1.55 eV) comp...

New halogen adducts of 1,3-dithiole-2-thione-4-carboxylic acid and dimethyl 1,3-dithiole-2-thione-4,5-dicarboxylate have been prepared and characterised by X-ray crystallographic studies. The adducts feature an array of intramolecular and intermolecular close contacts involving chalcogen-chalcogen, chalcogen-halogen and halogen-halogen interactions. Whilst these contacts are derived from the basic heterocyclic unit and the coordinated halogen molecules, the ester and acid functionalities provide a varied and rich array of hydrogen bonding motifs, which significantly enhance the long-range order of the supramolecular structures.

Poly(3,4-ethylenedithiathiophene) (PEDTT) is a polythiophene-like conjugated polymer in which each thiophene ring is functionalized with an ethylenedithia bridge. As such, PEDTT is the sulfur analogue of the well-known poly(3,4-ethylenedioxythiophene) (PEDOT). Substituent effects, namely the presence of sulfur atoms in PEDTT replacing the oxygen atoms of PEDOT, do not provide a simple explanation for the different electronic properties of the two polymers in the neutral state. This paper reports the spectroscopic properties of PEDTT, studied by in situ techniques such as IR-, Vis-, and electron spin resonance (ESR) spectroelectrochemistry. The differences observed upon electrochemical oxidation of PEDTT and PEDOT (e.g., the different infrared active vibrational band patterns in IR spectroelectrochemistry as well as the different nature of the charged states) are even more marked than those observed in the neutral state. These results, with AM1 calculations, indicate conformational effects as a possible explanation for the different electronic and spectroscopic properties of PEDTT and PEDOT.

A series of thiophene oligomers bearing core phenylene and fluorinated phenylene units has been synthesized as potential semiconductor materials for organic field-effect transistors (OFETs). Polymerization of these compounds has been achieved using Stille and oxidative Coupling methods. Functionalization of the phenylene unit with fluorine atoms has a marked effect on the self-assembly and electronic properties of the parent materials: the optical band gaps and highest occupied molecular orbital levels are affected with the introduction Of fluorine atoms as a result of a combination of inductive effects and rigidification of the main chain. The design of these materials has focused on the self-assembly and solution processability of the materials. All the polymers are readily Soluble in common organic solvents. Self-assembly and planarization of the fluorinated materials in the solid state are identified by a combination of X-ray diffraction studies, absorption spectroscopy, and cyclic voltammetry. The organizational behavior of the films is in contrast to the conformational freedom observed in solution (absorption spectroscopy) and in the gas phase (computational Studies). Thin-film OFETs have been fabricated for the entire polymer series. Hole mobilities have been measured Lip to 10(-3) cm(2)/(V(.)s), with high current modulation (on/off ratios up to 10(5)) and low turn-on voltages (down to 2 V). For the Stille Coupled polymers, replacement of the bridging thiophene unit with selenophene generally increases the hole mobility of the polymers.

We report the synthesis and electropolymerisation of 1,3,5-tris(1,3-dithiole-2-ylidenephenylene)benzene 4. The resulting polymer features extended tetrathiafulvalene (TTF) units and can be considered as a cross-conjugated, cross-linked structure. Upon p-doping, electrochemical and UV-vis spectroelectrochemical experiments indicate that the polymer undergoes a unique coformational change within the dendralene unit from one definitive orthogonal arrangement to another.

This paper describes the strategy toward novel monodisperse, well-defined, star-shaped oligofluorenes with a central truxene core and from monofluorene to quaterfluorene arms. Introduction of solubilizing n-hexyl groups at both fluorene and truxene moieties results in highly soluble, intrinsically two-dimensional nanosized macromolecules T1-T4. The radius for the largest oligomer of ca. 3.9 nm represents one of the largest known star-shaped conjugated systems. Cyclic voltammetry experiments reveal reversible or quasi-reversible oxidation and reduction processes (Eox = +0.74 to 0.80 V, Ered = -2.66 to 2.80 eV vs Fc/Fc+), demonstrating excellent electrochemical stability toward both p- and n-doping, while the band gaps of the oligomers are quite high (EgCV = 3.20-3.40 eV). Close band gaps of 3.05-3.29 eV have been estimated from the electron absorption spectra. These star-shaped macromolecules demonstrate good thermal stability (up to 400-420 degrees C) and improved glass transition temperatures with an increase in length of the oligofluorene arms (from Tg = 63 degrees C for T1 to 116 degrees C for T4) and show very efficient blue photoluminescence (lambdaPL = 398-422 nm) in both solution (PhiPL = 70-86%) and solid state (PhiPL = 43-60%). Spectroelectrochemical experiments reveal that compounds T1-T4 are stable electrochromic systems which change their color reversibly from colorless in the neutral state (approximately 340-400 nm) to colored (from red to purple color; approximately 500-600 nm) in the oxidized state.

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.

This chapter reviews original highlights in the chemistry of the Group 16 elements reported during 2003. The bulk of the review focuses on the chemistry/interaction of the chalcogens with other p-block elements. Due to the vast abundance and diversity of research into chalcogen chemistry, the report has been limited to materials with discrete molecular structure, either as novel products or reagents, or obtained by new synthetic strategies. The most important advances in 2003 include the isolation of hitherto unknown functionalities or bonding modes, unusual, unique or unexpected structures and a fascinating ferromagnet.

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.

A series of symmetrical 1,3-dithiole-2-thiones and -ones have been prepared via double lithiation of vinylene trithiocarbonate followed by trapping of the dianions with aryl carbaldehydes. The resulting diols are oxidised in high yield and the corresponding diketones are converted to thiophenes and furans using P2S5–NaHCO3 and P(OEt)3, respectively. The majority of triaryl compounds undergo two reversible oxidation processes in the range +0.86 to +1.57 V (vs. Ag/AgCl). The charge-transfer complex (8c)2·TCNQ forms mixed donor-acceptor stacks. EPR spectroscopy confirms the presence of an open shell species, but the material is an electrical insulator. Reaction of 8c with diiodine forms a charge transfer complex with a conductivity of 1.2 × 10−4 S cm−1.

Strong π-donors based on the association of TTF and 2,2′-bi(3,4-ethylenedioxy)thiophene conjugating unit have been synthesised; optical and an X-ray data show that intramolecular interactions lead to full rigidification of the conjugated system.

This Letter describes a fabrication of a microsensor incorporating a novel customised nitro-sensitive polymer derived from the propylenedioxythiophene family. Electrochemical polymerisation was used to selectively grow different types of localised polymer films on interdigitated electrode arrays, thereby fabricating miniature sensors that exhibited a highly selective and reversible response to chemical vapours containing ‘nitro’ (NO2) groups. Such nitro-bearing vapours are also present in trace quantities in the atmosphere in the presence of explosives. Vapours of nitropropane and nitrobenzene, serving as model analytes for explosives, were used for sensor testing. The sensors were demonstrated to have up to three orders of magnitude higher signal response to vapours from nitro compounds compared to other vapours commonly found in the atmosphere. The authors believe this is the highest selectivity to nitro compounds reported from a polymer-based chemicapacitor sensor.

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.

A new series of regioregular poly(terthiophenes), bearing bis(thioether) side groups, has been prepared by electrochemical oxidation. Cyclic voltammetry of the parent trimers reveals an increase in electron donating ability in cyclic thioether derivatives. For example, one compound containing a central ethylenedithiothiophene (EDTT) unit gives two irreversible oxidation peaks which are significantly lower than the corresponding values for the structurally analogous bis(methylthio) derivative (ΔE1ox = 170 mV, ΔE2ox = 30 mV). The difference in oxidation potentials of each terthiophene in acetonitrile solution can be explained by examining the highest occupied molecular orbital (HOMO) energies. The electrochemical behaviour of the polymers illustrates the increase in p-doping ability of the EDTT-containing polymer. The cyclic voltammograms and electronic absorption spectra of the polymers show that the polymers containing cyclic thioether units have the lowest bandgap in the series (ca. 1.4 V and 1.5 eV, respectively). Photoinduced IR spectroscopy of poly(dithienyl-3,4-ethylenedithiothiophene) provides evidence of a long-living photoexcited charged state in the polymer.

A novel BODIPY-containing organic small molecule is synthesized and employed as a down-converting layer on a commercial blue light-emitting diode (LED). The resulting hybrid device demonstrates white-light emission under low-current operation, with color coordinates of (0.34, 0.31) and an efficacy of 13.6 lm/W; four times greater than the parent blue LED.

Electrochemiluminescence (ECL) uses redox reactions to generate light at an electrode surface, and is gaining increasing attention for biosensor development due to its high sensitivity and excellent signal-to-noise ratio. ECL studies of monodisperse oligofluorene–truxenes (T4 series) have been reported previously, showing the production of stable radical cations and radical anions, generating blue ECL. The compound in this study differs from the original structures, in that there are 2,1,3-benzothiadazole (BT) units inserted between the first and second fluorene units of the quarterfluorenyl arms. It was therefore anticipated that the incorporation of these highly luminescent and ECL-active compounds into sensor development would lead to significant decreases in detection limits. In this contribution, we report on the impact of incorporating these novel complexes into sensor devices on the ECL efficiency, as well as the ability of these to improve the detection sensitivity and decrease the limit of detection using the reagent-free detection of model analytes. The real world impact of these compounds is elucidated through the comparison with more standard ECL materials such as ruthenium-based compounds. The potential for multiple applications is to be examined within this contribution.

In recent years, efforts have been made to introduce the heavier chalcogens into aromatic organic molecules that obey the Huckel rule (4n+2π-electrons), with a view to promoting and exploring their effect on electronic properties such as conductivity, magnetism, HOMO/LUMO energy levels, etc. Some of the fundamental properties of selenium and tellurium differ significantly from those of oxygen and sulfur, giving rise to disparities between the structures and properties of heavier chalcogen conducting materials when compared to their oxygen and sulfur-rich counterparts. In this chapter, we will focus on the state-of-the-art of selenium- and/or tellurium-rich derivatives of chalcogenophenes and tetrathiafulvalene that have been developed and studied for their application as organic conductors. Herein are presented carefully chosen examples and studies that illustrate how chalcogen chemistry and the replacement of oxygen and sulfur by the heavier selenium and tellurium chalcogens is used in the design and manipulation of electroactive materials, and ultimately how it affects suitability for molecular device applications. Finally, we will discuss the current state-of-the-art of these aromatic systems and the challenges presented in the synthesis and application of these materials in the field of organic electronics. Keywords: Aromaticity; chalcogenophene; charge transfer complex; fulvalenes; heterocyclic chemistry; organic electronics; organic semiconductor; radical conductors; secondary binding interactions

A series of hybrid tetrathiafulvalene-oligothiophene compounds has been synthesised, where the tetrathiafulvalene unit is fused at each side to an end-capped oligothiophene chain of varying length (terthiophene, quinquithiophene and septithiophene). Each hybrid structure (1-3) has been studied by cyclic voltammetry and triple EPR-UV-Vis-NIR spectroelectrochemistry in the case of the quinquithiophene compound (2). Comparison is made with the corresponding half-units, which lack the fulvalene core and contain just one oligothiophene chain. The highest hole mobility of quinquithiophene-TTF 2 was obtained from field effect transistors (8.61 × 10-3 cm 2 V-1 s-1); its surface morphology was characterised by tapping mode atomic force microscopy and a power conversion of 2.5% was achieved from a bulk heterojunction organic solar cell device using PC71BM as the acceptor.

The first example of an all-organic oligofluorene truxene based distributed feedback laser for the detection of a specific protein–small molecule interaction is reported. The protein avidin was detected down to View the MathML source1μgmL−1 using our biotin-labelled biosensor platform. This interaction was both selective and reversible when biotin was replaced with desthiobiotin. Avidin detection was not perturbed by Bovine Serum Albumin up to View the MathML source50,000μgmL−1. Our biosensor offers a new detection platform that is both highly sensitive, modular and potentially re-usable.

Charge transport has been studied in a germanium-centred oligothiophene cruciform featuring 2-D close packing in the bulk. The morphology has been found to play a significant role in charge carrier transport, evidenced by time-of-flight and field effect transistor measurements. Thermal step-annealing leads to the formation of smaller crystalline domains which are favourable for charge transport in device applications.

A novel polythiophene bearing a strong electron-accepting fluorene unit has been synthesized. Poly(2d) can be prepared by chemical (iron(III) chloride) or electrochemical oxidation. Intramolecular charge-transfer (ICT) within the polymer was studied by electronic absorption spectroscopy and compared to a series of model monomer derivatives. The redox properties of the materials were studied by cyclic voltammetry; polythiophene main chain in poly(2d) is oxidized at ca. +0.7 V vs Ag/AgCl, while the nitrofluorene repeat unit is reduced at ca. −0.5 and −0.7 V. The model compounds 3a−e show a Hammett-type correlation for ICT energies, E1red1/2 and E2red1/2 vs the substituents on the fluorene ring, with the sensitivity parameters ρICT- ≈ 0.17−0.20 eV and ρCV- ≈ 0.17−0.25 V. In contrast, the oxidation process (Eox) displays very low sensitivity to the structure of the fluorene ring (ρCV- ≈ 0.04 V), indicating that ICT can be substantially tuned without a noticeable effect on the redox properties of the thiophene...

New [3]- and [4]-dendralenes bearing electron-donor 1,3-dithiole and ferrocene substituents have been synthesised. Compounds 8, 15 and 17 have been characterised by single-crystal X-ray diffraction. Two of the dithiole rings of 8 are conjugated (dihedral angle 9 degrees), while the third dithiole ring is almost orthogonal to this plane, and hence its pi-electron system is isolated. For the dendralene precursor molecule 15, the substituted cyclopentadienyl ring, two C=C bonds and fused dithiole and dithiine rings comprise an extended pi-conjugated system. In molecule 17 the potential conjugation path C(6)C(3) C(4)C(5)-C5H5 is distorted by an 8 degrees twist around the C(3)-C(4) bond and a 7 degrees twist around the C(5)-C(21) bond, and the delocalisation along the chain is insignificant. Solution electrochemical data demonstrate that the dendralenes are strong pi-electron donors, which give rise to dication, radical trication or tetracation species. Spectroelectrochemical studies on compounds 7 and 10 suggest that the radical species are situated within the linear 1,2-ethylenediylidene moieties and that a conformational change may occur at the dication redox stage. UV/Vis spectroscopic data are consistent with poor cross-conjugation in these systems.

The synthesis is reported of a series of dipolar arylphosphonium salts bearing ferrocenylethenyl, 2-thienylethenyl, 4-dimethylaminophenylethenyl, or (4-dimethylaminophenyl)butadienyl electron-donor centres, together with a study of their course of alkaline hydrolysis, which provides a convenient synthetic route to related dipolar phosphine oxides. The phosphonium salts exhibit a modest degree of negative solvatochromism, whereas the related phosphine oxides show a small positive solvatochromic effect. In the case of the ferrocenyl systems, the electronic effects of the phosphorus acceptor group on the ferrocene unit have been studied by cyclic voltammetry.

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.

The compound 4,4-difluoro-4-borata-3a-azonia-4a-aza-s-indacene, more commonly known as BODIPY, has enjoyed a high and rapidly escalating level of interest over the past decade.(1) This dye-type material, which can be likened to a porphyrin subunit, has been studied mainly in applications related to its strong absorption and fluorescence properties.(2, 3) Recent examples of the applications of BODIPY include biological tags with visible/near IR emission,(4, 5) mechanical rotors,(6) lasing,(7-9) dye sensitized solar cells,(10) electroluminescence (EL),(11) and electrogenerated chemiluminescence (ECL).

The syntheses of a series of 1,3-dithiole-2-thione derivatives (3-6), bearing fused terthiophene or bis(2-thienyl)-2,5-furan units, are reported. These novel heterocycles are readily polymerized electrochemically to give stable electroactive materials. The target compounds were obtained in moderate to high yield via the cyclization of the corresponding diketones or hydroxyketones, using phosphorus pentasulfide or acidic conditions. The ketones 12 and 17 were prepared directly from their hydroxy precursors by treatment with MnO2. The trans configuration of diketone 20 was confirmed by X-ray crystallography.

Under strongly acidic conditions, the title compound 1 readily participates in several possible rearrangement pathways, affording a product distribution which is relative to the choice of solvent and acid catalyst. Thus, using chloroform or acetone as the solvents and HBr or HClO4 as the catalysts, compounds 2–4 have been isolated and fully characterised; in addition, compound 5 was identified in the reaction mixture and characterised by 1H NMR spectroscopy. The reaction kinetics of the transformations have been studied by 1H NMR spectroscopy, using deuterated chloroform or acetone as the NMR solvents. A key intermediate in the reaction mechanisms is the allylic carbocation 6, which rearranges to give the fused system 3; in the presence of bromide anions, the carbocation forms an ion-pair intermediate 7, leading to the formation of compounds 2, 4 and/or 5, depending on the solvent.

The degree of intramolecular charge transfer (ICT) in 9-(1,3-dithiol-2-ylidene)fluorenes bearing fused thiophene and 2,5-dihydrothiophene units (2 and 16, respectively), has been investigated by UV-VIS spectroscopy. Both series of compounds show a good correlation between the ICT energies and Σσp– values of the corresponding molecules. The sensitivity parameters ρICT– are 0.18 eV for 2 and 0.16 eV for 16. Cyclic voltammetry of both series, 2 and 16, reveals a single irreversible oxidation process in all compounds. However, electropolymerisation under oxidative conditions does not take place, since the radical cation intermediate is most probably derived from the electroactivity of the 1,3-dithiole–fluorene fragment. In parallel to ICT, the values of E1red½ and E2red½ in relevant compounds also show a linear relationship with σp– constants in the fluorene ring. The sensitivity parameters for series 2 are 0.20 V (ρ1red–) and 0.17 V (ρ2red–), whilst those for 16 are 0.26 V (ρ1red–) and 0.18 V (ρ2red–).

Reaction of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione 1 with diiodine or iodine monobromide in CH2Cl2 resulted in the formation of molecular charge-transfer complexes 1·I2 and 1·IBr respectively. Both complexes have been characterised crystallographically and contain a linear S–I–X (X = I or Br) moiety with the sulfur adopting a tetrahedral geometry taking into account the stereochemically active lone pairs. The S–I [2.716(3)] and I–I [2.808(3) A] bond lengths in 1·I2 are similar to those reported for diiodine complexes of related thione donors. The adduct 1·IBr is the first crystallographically characterised thione–iodine monobromide charge-transfer complex. The S–I distance [2.589(2) A] is shorter than that in 1·I2, consistent with IBr being a stronger acceptor than I2. The I–Br distance [2.7138(11) A] is lengthened with respect to that in unco-ordinated IBr, but within bonding distance when compared to the sum of the van der Waals radii for iodine and bromine (3.75 A). Treatment of 1 with dibromine under identical conditions resulted in the formation of the adduct 1·Br2 and the dithiolylium salt [C5H6S4Br][Br3]·½Br2 2. Treatment of 1 with Br2 in toluene led to the isolation of 1·Br2 only. The crystal structure of 1·Br2 shows the compound to contain a linear Br–S–Br moiety with the sulfur in a T-shaped or Ψ-trigonal bipyramidal environment (taking into account the stereochemically active lone pairs). The structure of 2 reveals a three component system consisting of the [C5H6S4Br]+ cation, the [Br3]– anion and a molecule of Br2 in a 2∶2∶1 ratio. These components are held in the lattice by a series of weak intermolecular interactions which link the tribromide ions and dibromine molecules into zigzag chains.