Search

Judiciously designed phthalocyanines (Pcs), such as silicon-Pc bis(3,5-diphenyl)benzoate (1c), with axial substituents which prevent aggregation, can self-assemble to form ordered nanoporous films on electrode surfaces. In this paper, complementary techniques such as Scanning Kelvin Nanoprobe (SKN) microscopy, Atom Force Microscopy (AFM) and electrochemical measurements are used to demonstrate that films formed by silicon-Pc bis(3,5-diphenyl)benzoate allow size- and charge- selective transport of probe molecules through well-defined intermolecular cavities. In contrast, the analogs silicon-Pc bis(4-tert-butylbenzoate) (1a) and silicon-Pc bis(3-thienyl)acetate (1b) have different film morphologies when solvent-cast in the same manner and block the electrode surface. The role of the different axial substituents in orienting the molecules on the substrate is discussed.

A new series of platinum(II) complexes containing cyclometallated diaryl ketimine ligands has been synthesised. The route involves reaction of diaryl ketimines with K[PtCl3(dmso)] to obtain trans-[PtCl2(imine)(dmso)] species, which underwent cyclometallation upon heating in toluene to give [PtCl{Ar′(ArC=NH)}(dmso)] complexes 12b–17b. N-Hydroxy and N-phenyl analogues 18b and 21 were also synthesised. In complexes 19 and 20 the auxiliary chlorido and dmso ligands were replaced by an acetylacetonato ligand. The photophysical properties of the cyclometallated complexes are reported. The emission bands at λmax ≈ 450 and 550 nm are assigned to mixed-ligand and MLCT states having significant singlet and triplet character, respectively. By varying the structure of the aromatic ligand the efficiency of phosphorescence can be increased to 4.3 % for 15b (Ar′ = 1-naphthyl). Theoretical calculations show that the low-energy transitions in all the cyclometallated systems involve mainly the frontier orbitals, HOMO and LUMO. These are mixed chlorido–metal–ligand to largely π*-C=N transitions. Most of the observed phosphorescence data can be explained by the geometric change on going from the S0 to the T1 states. An organic light-emitting device has been fabricated by using complex 15b as the emissive dopant in a poly(vinylcarbazole) host. Broad electroluminescence spanning the range 500–750 nm was observed.

Studies are reported on a series of triphenylamine–(C[TRIPLE BOND]C)n–2,5-diphenyl-1,3,4-oxadiazole dyad molecules (n=1–4, 1, 2, 3 and 4, respectively) and the related triphenylamine-C6H4–(C[TRIPLE BOND]C)3–oxadiazole dyad 5. The oligoyne-linked D–π–A (D=electron donor, A=electron acceptor) dyad systems have been synthesised by palladium-catalysed cross-coupling of terminal alkynyl and butadiynyl synthons with the corresponding bromoalkynyl moieties. Cyclic voltammetric studies reveal a reduction in the HOMO–LUMO gap in the series of compounds 1–4 as the oligoyne chain length increases, which is consistent with extended conjugation through the elongated bridges. Photophysical studies provide new insights into conjugative effects in oligoyne molecular wires. In non-polar solvents the emission from these dyad systems has two different origins: a locally excited (LE) state, which is responsible for a π*[RIGHTWARDS ARROW]π fluorescence, and an intramolecular charge transfer (ICT) state, which produces charge-transfer emission. In polar solvents the LE state emission vanishes and only ICT emission is observed. This emission displays strong solvatochromism and analysis according to the Lippert–Mataga–Oshika formalism shows significant ICT for all the luminescent compounds with high efficiency even for the longer more conjugated systems. The excited-state properties of the dyads in non-polar solvents vary with the extent of conjugation. For more conjugated systems a fast non-radiative route dominates the excited-state decay and follows the Engelman–Jortner energy gap law. The data suggest that the non-radiative decay is driven by the weak coupling limit.

A one-pot synthesis of 2-chloro-3,4-diiodopyridine from 2-chloropyridine is described via a Directed ortho Metallation (DoM)/Halogen Dance (HD) mechanism in 26–28% yields. By performing sequential, iterative Suzuki–Miyaura cross-couplings using a variety of functionalised heteroaryl and arylboronic acids, a series of novel 2,3,4-triheteroarylpyridine scaffolds have been accessed in synthetically viable yields, including sterically hindered derivatives. 2-Chloro-4-heteroaryl-3-iodopyridines and 2-chloro-3,4-diheteroarylpyridines are also reported. The synthesis of 5-[3,4-bis(2-phenylethynyl)pyridin-2-yl]-2-fluoropyridine via a two-step Sonogashira/Suzuki–Miyaura reaction sequence from 2-chloro-3,4-diiodopyridine, phenylacetylene and 6-fluoropyridin-3-yl-3-boronic acid has been achieved in 48% overall yield.

A series of {(9,9-dioctylfluorene)(0.7-x)-(dibenzothiophene-S,S-dioxide)(0.3)-[4,7-bis(2-thienyl)-2,1,3-benzothiadiazole](x)} (PFS(30)-TBTx), where x represents the minor percentage of the red emitter 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) randomly incorporated into the copolymer backbone, is investigated in order to follow the energy transfer from PFS(30) to TBT moieties. The emission of the donor poly[(9,9-dioctylfluorene)(0.7)-(dibenzothiophene-S,S-dioxide)(0.3) identified by PFS(30) and peaking at 450 nm, is clearly quenched by the presence of the red TBT chromophore emitting at 612 nm, with an isoemissive point observed when the spectra are collected as a function of temperature. A plot of the ratio between the TBT and PFS(30) emissions as a function of the reciprocal of temperature gives a clear linear trend between 290 and 200 K, with an activation energy of 20 meV and showing a turn over to a non-activated regime below 200 K. Picosecond time-resolved fluorescence decays collected at the PFS(30) and TBT emission wavelengths, show a decay of the PFS(30) emission and a fast build-in, followed by a decay, of the TBT emission, confirming that the population of the TBT excited state occurs during the PFS(30) lifetime (approximately 600 ps). The population of the TBT excited state occurs on a time regime around 150 ps at 290 K, showing an energy barrier of 20 meV that turns over to a non-activated regime below 200 K in clear agreement with the steady-state data. The origin of the activation barrier is attributed to the presence of physical and energetic disorder, affected by fast thermal fluctuations that dynamically change the energy landscape and control the exciton migration through the polymer density of states.

Here, the photophysics and performance of single-layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae and where ppy, bpy, and phen are 2-phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the NˆN ligand has little effect on the emitting metal-ligand to ligand charge-transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000 cd m−2 at 3 V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents.

A description of the synthesis of random (9,9-dioctylfluorene-2,7-diyl)–(dibenzothiophene-S,S-dioxide-3,7-diyl) co-polymers (p(F-S)x) by palladium-catalyzed Suzuki cross-coupling polymerization where the feed ratio of the latter is varied from 2 to 30 mol % (i.e., x = 2–30) is given. Polymer light emitting devices are fabricated with the configuration indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/p(F–S)x/Ba/Al. The device external quantum efficiency increased as the ratio of the S co-monomer was increased, up to a maximum of 1.3% at 100 mA cm−2 for p(F-S)30 and a brightness of 3 770 cd m−2 (at 10 V). The S units impart improved electron injection, more balanced mobilities, and markedly improved device performance compared to poly(9,9-dioctylfluorene) under similar conditions. These co-polymers display broad emission, observed as greenish-white light, which arises from dual fluorescence, viz. both local excited states and charge transfer states. Utilizing dual emission can reduce problems associated with Forster energy transfer from high-energy to-low energy excited states.

Arylation reactions of NH-heterocycles [specifically, pyrazole, 3-(trifluoromethyl)pyrazole, imidazole and pyrrole] with 2,4-difluoroiodobenzene in the absence and presence of copper catalysis are described. The combination of fluoro and iodo substituents in the same aryl substrate has facilitated both SNAr reactions at the C–F bonds and copper-catalysed Ullmann-type coupling reactions at the C–I bond. Products arising from regioselective reactions and multiple substitutions have been isolated, providing a range of new N-arylated pyrazole, imidazole and pyrrole derivatives.

The synthesis and isolation is reported of five terminal aryl/biaryl-butadiynes, Ar–C≡C–C≡CH, (5a–c, 10a and 10b) from 2-methyl-6-aryl/biaryl-hexa-3,5-diyn-2-ol precursors [Ar–C≡C–C≡C–C(Me)2OH; Ar = 2-MeOC6H4, 3-MeOC6H4, 4-MeOC6H4, 2-phenylpyridin-5-yl, 3-phenylpyridin-2-yl, respectively]. The X-ray crystal structures have been obtained for compounds 5c and 10a. Surprisingly, no ≡C–H···X (X = N or O) hydrogen bonds exist in the crystals of 5c and 10a. These structures illustrate the fact that ≡C–H···X hydrogen bonds are not always reliable tools for crystal engineering. Palladium-catalysed cross-coupling of 5c with 2-iodopyrimidine gave the unsymmetrical 1,4-diarylbutadiyne derivative 12; copper-catalysed reactions of 5c and 10a with benzyl azide proceeded regioselectively to give alkynyltriazoles 13 and 14.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Unprecedented stability has been observed in terminal aryl hexatriyne and terminal aryl octatetrayne derivatives by judicious choice of a bulky, nonplanar headgroup [viz., 4-(3,6-di-tert-butyl-N-carbazolyl)phenyl] which hinders topochemical intermolecular interactions in the crystal lattice.

This paper describes copper-catalyzed N–C heteroarylation of benzimidazole, 1-methylbenzimidazolone, imidazole and pyrrole. The products of these reactions then undergo palladium-catalyzed C–C cross-couplings with aryl or heteroarylboronic acids under Suzuki–Miyaura conditions to provide a rapid entry, from readily-available reagents, into tris(hetero)aryl scaffolds comprising two or three N-heterocyclic rings. The sequential N–C and C–C couplings can be performed in a one-pot process (two examples are given: >50 % overall yields). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The singlet excited-state dynamics in poly[(9,9-dioctylfluorene)-(dibenzothiophene-S,S-dioxide)] (PFSx ) random copolymers with different contents of dibenzothiophene-S,S-dioxide (S) units have been studied by steady-state and time resolved fluorescence spectroscopies. Emission from PFSx copolymers shows a pronounced solvatochromism in polar chloroform, relative to the less polar toluene. An excited intramolecular charge transfer state (ICT) is stabilized by dipole-dipole interactions with the polar solvent cage, and possibly accompanied by conformational rearrangement of the molecular structure, in complete analogy with their small oligomer counterparts. The spectral dynamics clearly show that the ICT stabilization is strongly affected by the surrounding medium. In the solid state, emission from PFSx copolymers depends on the content of S units, showing an increase of inhomogeneous broadening and a red shift of the optical transitions. This observation is consistent with stabilization of the emissive ICT state, by the local reorientation of the surrounding molecules at the location of the excited chromophore, which results in favorable dipole-dipole interactions driven by the increase in the dielectric constant of the bulk polymer matrix with increasing S content, in analogy to what happens in polar solvent studies. Furthermore, in clear agreement with the interpretation described above, a strong increase in the emission quantum efficiency is observed in the solid state by decreasing the temperature and freezing out the molecular torsions and dipole-dipole interactions necessary to stabilize the ICT state.

Attaching electron-rich 1,3-dithiol-2-ylidene moieties to polynitrofluorene electron acceptors leads to the formation of highly conjugated compounds 6 to 11, which combine high electron affinity with a pronounced intramolecular charge transfer (ICT) that is manifested as an intense absorption band in their visible spectra. Such a rare combination of optical and electronic properties is beneficial for several applications in optoelectronics. Thus, incorporation of fluorene-dithiole derivative 6 a into photoconductive films affords photothermoplastic storage media with dramatically increased photosensitivity in the ICT region. A wide structural variation of the dithiole and fluorene parts of the molecules reveals excellent correlation between the ICT energy and the reduction potential with the Hammett's parameters for the substituents. Although only a small solvatochromism of the ICT band was observed, heating the solution led to a pronounced blueshift, which was probably as a result of increased twisting around the C9=C14 bond that links the fluorene and dithiole moieties. X-ray crystallographic analysis of 7a, 8a, 10a, 11 a and 13 a confirms an ICT interaction in the ground state of the molecules. The C9=C14 double bond between the donor and acceptor is substantially elongated and its length increases as the donor character of the dithiole moiety is enhanced.

We report the synthesis of (2,6-dimethoxy-3-pyridyl)boronic acid (2), (2,3-dimethoxy-4-pyridyl)boronic acid (4), (2,6-difluoro-3-pyridyl)boronic acid (6), (2,6-dichloro-3-pyridyl)boronic acid (8) and (2,3-dichloro-4-pyridyl)boronic acid (10) by directed ortho-metalation reactions on the corresponding disubstituted pyridine precursor, followed by the reaction with triisopropyl borate (TPB) or trimethyl borate. Thereactivity of the pyridylboronic acids with heteroaryl halides in Suzuki–Miyaura cross-coupling reactions has been evaluated. New highly functionalized heteroarylpyridine derivatives have thereby been obtained in moderate to high yields. The reaction of 8 and 3-amino-2-chloropyridine yielded the rare 5H-pyrrolo[2,3-b:4,5-b′]dipyridine (i.e. 1,5-diazacarbazole) ring system by sequential cross-coupling and intramolecular cyclisation reactions. The X-ray crystal structures are reported for the pyridylboronic acids 2, 4, 8 and 10. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A general method for the synthesis of functionalized pyridazinylboronic acids/esters is described involving a directed ortho metalation (DoM)--boronation protocol (Schemes 1 and 2). A comprehensive study of the reactivity of the C-B bond in palladium-catalyzed cross-couplings with aryl/heteroaryl halides is presented. Aryl-/heteroarylpyridazines are thereby obtained in synthetically viable yields (typically 40-75%) although in some cases competing protodeboronation has been observed. A series of pyridazin-3(2H)-one derivatives, including 4,6-diaryl/heteroaryl derivatives, have been obtained from the corresponding 3-methoxypyridazines in straightforward procedures (Schemes 3 and 4). Several X-ray crystal structures of aryl-/heteroarylpyridazines and derived pyridazin-3(2H)-one derivatives are reported. These multi-ring systems are of considerable interest in contemporary N-heterocyclic chemistry.

Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ‐DBTO2, showing thermally activated delayed fluorescence (TADF), with near‐orthogonal electron donor (D) and acceptor (A) units is reported. It is shown that DPTZ‐DBTO2 has minimal singlet–triplet energy splitting due to its near‐rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D–A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near‐degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ‐DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D–A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.

A three-color warm-white organic light-emitting diode employing an efficient phosphor-phosphor type host-guest emitting system achieves efficiencies of 27.3% for external quantum efficiency and 74.5 lm W(-1) for power efficiency at a luminance of 1000 cd m(-2) , which maintained the high levels of 24.3% and 45.8 lm W(-1) at 10 000 cd m(-2) , with a stable color-rendering index of 86-87.

A series of phenothiazine-dibenzothiophene-S,S-dioxide charge-transfer molecules have been synthesized. Increasing steric restriction around the donor-acceptor bond significantly alters contributions from TADF and phosphorescence. Bulky substituents on the 1-(and 9) position(s) of the phenothiazine result in no TADF in the solid state; instead strong phosphorescence is observed at ambient temperature.

The conductance and the decay of conductance as a function of molecular length within a homologous series of oligoynes, MeSi - (C≡C) - SiMe (n = 2, 3, 4, or 5), is shown to depend strongly on the solvent medium. Single molecule junction conductance measurements have been made with the I(s) method for each member of the series MeSi - (C≡C) - SiMe (n = 2, 3, 4, and 5) in mesitylene (MES), 1,2,4-trichlorobenzene (TCB), and propylene carbonate (PC). In mesitylene, a lower conductance is obtained across the whole series with a higher length decay (β ≈ 1 nm). In contrast, measurements in 1,2,4-trichlorobenzene and propylene carbonate give higher conductance values with lower length decay (β ≈ 0.1 and 0.5 nm respectively). This behavior is rationalized through theoretical and computational investigations, where β values are found to be higher when the contact Fermi energies are close to the middle of the HOMO-LUMO gap but decrease as the Fermi energies approach resonance with either the occupied or unoccupied frontier orbitals. The different conductance and β values between MES, PC, and TCB have been further explored using DFT-based models of the molecular junction, which include solvent molecules interacting with the oligoyne backbone. Good agreement between the experimental results and these >solvated> junction models is achieved, giving new insights into how solvent can influence charge transport in oligoyne-based single molecule junctions., D.C.M., S.J.H., R.J.N., P.J.L., and S.M-G. thank EPSRC for funding (EPSRC Grants EP/K007785/1, EP/H035184/1, and EP/K007548/1). P.J.L. holds an ARC Future Fellowship (FT120100073) and gratefully acknowledges funding for this work from the ARC (DP140100855). C.J.L. and O.A.A. acknowledge financial support from the Ministry of Higher Education and Scientific Research of Iraq. V.M.G.-S. thanks the Spanish Ministerio de Economıa y Competitividad for a Ramoń y Cajal fellowship (RYC-2010-06053). J.F. and V.M.G.-S. acknowledge financial support from the Spanish MICINN Grant FIS2012-34858 and the Marie Curie Network MOLESCO. They also acknowledge the supercomputing facility CESGA where part of the calculations was carried out. P.C. and S.M. are grateful for financial assistance from Ministerio de Economia y Competitividad from Spain in the framework of the project CTQ2012-33198 as well as the award of the CTQ2013-50187-EXP grant. P.C and S.M. thank the DGA and Fondos FEDER for funding for the Platon research group. S.M. thanks the Ministerio de Educacion of Spain for financial support in the framework of the Campus de Excelencia Internacional, CEI Iberus. M.R.B. and C.J.L. acknowledge funding from the EU through the FP7 ITN MOLESCO (Project Number 212942).

We determine and compare, at the single molecule level and under identical environmental conditions, the electrical conductance of four conjugated phenylene oligomers comprising terminal sulfur anchor groups with simple structural and conjugation variations. The comparison shows that the conductance of oligo(phenylene vinylene) (OPV) is slightly higher than that of oligo(phenylene ethynylene) (OPE). We find that solubilizing side groups do neither prevent the molecules from being anchored within a break junction nor noticeably influence the conductance value.

We report the synthesis of 2-chloro-5-pyrimidylboronic acid (6) and 2-amino-5-pyrimidylboronic acid (8) by lithium–halogen exchange followed by reaction with triisopropylborate. Their reactivity with heteroaryl halides in Suzuki–Miyaura cross-coupling reactions has been evaluated. New highly functionalized 5-heteroarylpyrimidine derivatives 24–33 (heteroaryl = quinoline, pyridine, pyrimidine, pyrazine, thiophene, benzothiazole) have been obtained in synthetically useful yields. The X-ray structure of 6 reveals extensive intermolecular O–H···N hydrogen bonding in the crystal. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The first cyclometalated dibenzothiophene S,S-dioxide derivative, namely [fac-2-(5,5-dioxidodibenzothiophen-3-yl)pyridine]iridium(III) (3) has been synthesised in high yield and characterised by X-ray crystallography, solution electrochemistry, absorption and emission spectroscopy. The Ir atom has a fac-octahedral coordination with three chelating ligands (A, B and C); each Ir–N bond is in trans position to an Ir–C bond. In cyclic voltammetry experiments in dichloromethane, complex 3 undergoes a reversible metal-centred IrIII/IrIV oxidation at E1/2ox = +1.04 V vs. Ag/Ag+ reference electrode. Complex 3 exhibits bright green photoluminescence (λmax = 525 nm in toluene) from mixed 3MLCT/3ππ* states with quantum yield (ΦPL) of 0.26 in toluene solution. The phosphorescence emission decay follows first order kinetics, with a lifetime of 4.9 μs. A comparison of complex 3 with analogues 1 and 2, where the dibenzothiophene S,S-dioxide unit is replaced by 9,9-dihexylfluorene and N-hexylcarbazole respectively, establish that the substituent para to the Ir metal atom, i.e. CR2 in 1, NR in 2 and SO2 in 3, has a major influence on the redox and emission properties in this series. Organic light-emitting diodes (OLEDs) were fabricated by spin-coating techniques using a polyspirobifluorene copolymer (PSBF) as a host and complex 3 as dopant.In a single-layer blend configuration ITO/PEDOT:PSS/PSBF:3(8 wt.-%)/Ba/Al OLEDs showed pale blue/white light emission (CIE coordinates: x = 0.29, y = 0.31) arising from a combination of fluorescence from the host copolymer (λmax = 450 nm) and phosphorescence from 3 (λmax = 530 nm). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Involuntary psychiatric treatment is sometimes necessary and beneficial, but may also exert negative effects. The impact of involuntary commitment on subsequent mental health treatment experience is poorly understood. We examined whether history of involuntary commitment was associated with current perceptions of coercion in a sample of voluntarily hospitalized veterans (N = 205). In adjusted analyses, perceived coercion during the voluntary admission was significantly associated with prior history of involuntary commitment (Rate Ratio = 1.60, p = .05). Perceived coercion was also higher among participants who were married/cohabiting (Rate Ratio = 1.83, p = .01) and among those with greater functional impairment (Rate Ratio = 0.97, p = .04). Although frequently unavoidable, the current results underscore the potential negative effects of coercive practices such as involuntary commitment, and support the importance of policies that aim to minimize coercive treatment experiences among psychiatric patients.

Two complementary series of C(60)-(Fl)(n) and C(60)-(Fl)(n)-C60 (Fl = 9,9-dihexylfluorene-2,7-diyl; n = 1-5) derivatives with terminal N-methylfulleropyrrolidine units have been synthesized from CHO-(Fl)(n) and CHO-(Fl)(n)-CHO precursors via 1,3-dipolar cycloaddition reaction of in situ generated azomethine ylides with an excess of C60. In solution electrochemical experiments, these conjugates give rise to amphoteric redox behavior. Three consecutive quasireversible reduction waves have been observed at the expected potentials for the N-methylfulleropyrrolidine cores. For the C(60)-(Fl)(n)-C(60) series, each reduction wave is a two-electron process with no observable interaction between the C(60) units. Two or, in some cases, three oxidation waves--most of them irreversible--are ascribed to the oligofluorene system. These waves are cathodically shifted with an increasing number of fluorene units and anodically shifted by the conjugated terminal aldehyde units, compared to the N-methylfulleropyrrolidine termini. Steady-state and time-resolved photolytic techniques show that an efficient transduction of singlet excited-state energy transfer prevails from the photoexcited oligofluorene to the energy accepting fullerene.

The synthesis and photophysical properties are described for a series of porphyrin, phthalocyanine and pyrazinoporphyrazine derivatives which bear four or eight peripheral fluorenyl substituents as antennae. Representative examples are 5,10,15,20-tetra(9,9-dihexyl-9H-fluoren-2-yl)porphyrin (2), 5,10,15,20-tetrakis[4-(9,9-dihexyl-9H-fluoren-2-yl)phenyl]porphyrin (3), 2,3,9,10,16,17,23,24-octakis(9,9-dihexyl-9H-fluoren-2-yl)-29H,31H-phthalocyanine (8) and 2,3,9,10,16,17,23,24-octakis[4-(9,9-dihexyl-9H-fluoren-2-yl)phenyl]-29H,31H-tetrapyrazinoporphyrazine (9). Palladium-mediated Suzuki-Miyaura cross-coupling reactions have been key steps for attaching the substituents. The compounds are deep-red emitters: lambda(max)(em)=659 (3), 737 (8) and 684 nm (9). Their absorption and emission spectra, their fluorescence lifetimes and quantum yields are correlated with the structures of the macrocycles and the substituents. The solution fluorescence quantum yields of porphyrin derivatives substituted with fluorene (2-4) and terphenyl substituents (7) (Phi(f)=0.21-0.23) are approximately twice that of tetraphenylporphyrin. For phthalocyanine derivative 8, Phi(f) was very high (0.88). Specific excitation of the fluorene units of 8 produced emission from both of them (lambda(max)=480 nm) and also from the phthalocyanine core (lambda(max)=750 nm), indicating a competitive rate of energy transfer and radiative decay of the fluorenes. Organic light-emitting devices (OLEDs) were made by spin-coating techniques by using a polyspirobifluorene (PSBF) copolymer as the host blended with 3 (5 wt. %) in the configuration ITO/PEDOT:PSS/PSBF copolymer:3/Ca/Al. Deep-red emission (lambda(max)=663 nm; CIE coordinates x=0.70, y=0.27) was observed with an external quantum efficiency of 2.5 % (photons/electron) (at 7.5 mA cm(-2)), a low turn-on voltage and high emission intensity (luminance) of 5500 cd m(-2) (at 250 mA/ m(2)).

Using ligands synthesized by Suzuki cross-coupling methodology, new phosphorescent homoleptic tris-cyclometalated complexes have been obtained, namely fac-[Ir(Cz-2-Fl(n)Py)(3)] (1 d-f) and fac-[Ir(Cz-3-Fl(n)Py)(3)] (2 d-f), which are solution-processible triplet emitters (Cz denotes N-hexylcarbazole, n is the number of 9,9'-dihexylfluorene (Fl) units (n=0,1,2) and Py is pyridine). In all cases, Py and Fl are substituted at the 2- and 2,7-positions, respectively, and Cz moieties are substituted by either Py or Fl at the 2- or 3-positions, in series 1 and 2, respectively. The oxidation potential of 1 d studied by cyclic voltammetry ({E{{{\rm ox}\hfill \atop 1/2\hfill}}}=0.14 V, versus Ag/AgNO(3), CH(2)Cl(2)) is less positive (i.e. raised HOMO level) compared to that of the isomer 2 d ({E{{{\rm ox}\hfill \atop 1/2\hfill}}}=0.30 V), where the Cz-nitrogen is meta to the Ir center. Ligand-centered oxidations occur at more positive potentials, leading to 7+ oxidation states with good chemical reversibility and electrochemical quasi-reversibility, for example, for 2 f {E{{{\rm ox}\hfill \atop {\rm pa}\hfill}}} =0.45 (1e), 0.95 (3e), 1.24 V (3e). Striking differences are seen in the solution-state photophysical data between complexes [Ir(Cz-2-Py)(3)] (1 d) and [Ir(Cz-3-Py)(3)] (2 d), in which the Cz moiety is bonded directly to the metal center: for the latter there is an 85 nm blue-shift in emission, a decrease in the luminescence lifetime and an increase in the PLQY value. Organic light emitting devices were made by spin-coating using polyspirobifluorene:bis(triphenyl)diamine (PSBF:TAD) copolymer as host and the complexes 1 d or 2 d as dopants. Turn-on voltages are low (3-4 V). With 1 d orange light is emitted at lambda(max)=590 nm with an EQE of 1.3 % (at 7.5 mA cm(-2)) and an emission intensity (luminance) of 4354 cd m(-2) (at 267 mA m(-2)). The green emission from 2 d devices (lambda(max)=500 nm) is due to the reduced electron-donating ability of the carbazole unit in 2 d. Recording the EL spectra of the 1 d device at 6 V (current density, 100 mA cm(-2)) established that the time to half brightness was about 9 h under continuous operation with no change in the spectral profile, confirming the high chemical stability of the complex.

Efficient aggregation induced phosphorescence emission (AIPE) of an ionic Ir(iii) complex occurs when the counterion (PF6(-)) is exchanged specifically by ClO4(-) in aqueous media. As a result, a rapid, highly selective "turn-on" phosphorescent response to ClO4(-) is observed in aqueous media. These studies pave the way for a new efficient phosphorescence-based detection strategy for anions.

This study establishes that the structure of the linker group between the hydrophobic and hydrophilic units in the new surfactants 1–13 plays an important role in the dispersibility of multiwalled carbon nanotubes (MWNTs) in water. The systematic variation of the linker group in amphiphilic surfactants for carbon nanotubes has not been previously investigated. In the present series, the hydrophobic unit is derived from pyrene, the hydrophilic unit comprises 1–9 carboxylate groups and the linker is based on amide or ether moieties. The resulting MWNT–surfactant dispersions, up to concentrations and efficiencies of ca. 160 mg L−1 and almost 50%, respectively, have been characterised by UV-vis absorption spectroscopy studies which provide detailed structure–property relationships, while transmission electron microscopy (TEM) was used to confirm that the MWNTs were well dispersed. For many of the new surfactants enhanced dispersion efficiency is observed compared to commercial surfactants. The efficiency of the dispersion is affected by the presence, functionality and particularly the length of the linker, and also the number of terminal carboxylate units. The marked effect of sodium, potassium and calcium cations on the dispersion behaviour is explained by interactions between the metal ions and the surfactant and an ionic screening mechanism. We also demonstrate that the dispersibility of the MWNT–surfactant dispersions can be reversibly switched ‘off’ and ‘on’ by addition of acid and base, respectively. The experimental results are supported by theoretical calculations of solvation energy ΔES. This study represents a significant advance in the design of multi-functional surfactants for efficient aqueous dispersions of carbon-based materials.

Two new AIE-active dinuclear Schiff base Ir(III) complexes exhibit highly reversible piezochromic phosphorescence behaviour enabling the construction of a re-writable phosphorescence data recording device.

The Pd(PPh3)4/CuI-cocatalyzed reaction of Ru(C≡CC≡CH)(PPh3)2Cp (2) with aryl iodides, Ar–I (3, Ar = C6H4CN-4 (a); C6H4Me-4 (b); C6H4OMe-4 (c); 2,3-dihydrobenzo[b]thiophene (d); C5H4N (e)) proceeds smoothly in diisopropylamine and under an inert atmosphere to give the substituted buta-1,3-diynyl complexes Ru(C≡CC≡CAr)(PPh3)2Cp (4a–e) in moderate to good yield. The procedure allows the rapid preparation of a range of metal complexes of arylbuta-1,3-diynyl ligands without necessitating the prior synthesis of the individual buta-1,3-diynes as ligand precursors. Similar reaction of 2 with half an equivalent of 1,4-diiodobenzene affords the bimetallic derivative {Ru(PPh3)2Cp}2(μ-C≡CC≡C-1,4-C6H4–C≡CC≡C) (5). In the presence of atmospheric oxygen, homocoupling of the diynyl reagent 2 takes place to provide the octa-1,3,5,7-tetrayndiyl complex {Ru(PPh3)2Cp}2(μ-C≡CC≡CC≡CC≡C) (6). Crystallographically determined molecular structures are reported for five complexes (4a, 4b, 4d, 5, and 6). Quantum chemical calculations indicate that the HOMOs are mainly located on the C4–C6H4–C4 and C8 bridges for 5 and 6, respectively, while spectroelectrochemical (UV–vis–NIR and IR) studies on 6 establish that oxidation takes place at the C8 bridge, likely followed by cyclodimerization reactions of the bridging ligand.

Two new deep blue emitting co-polymers are synthesised and exploited in highly-efficient solution-processed polymer light-emitting diodes (PLEDs). A key molecular design feature is selective functionalisation of 9,9-diphenylfluorene to disrupt backbone π-conjugation, thereby promoting luminescence from short emissive domains (λELmax 422 and 401 nm for P1 and P2 devices, respectively). PLEDs using P1 and P2 in the hybrid architecture ITO/PEDOT:PSS/polymer/TPBi/LiF/Al show low turn-on voltages and remarkably high EQE values of ηext,max 3.3%, Lmax of 167 cd m−2 with CIExy coordinates (0.17, 0.10) for P1; and 3.9%, 274 cd m−2, CIExy (0.17, 0.07) for P2. These performances are currently among the best for PLEDs with CIEy ≤ 0.10.

Electrical and mechanical properties of elongated gold-molecule-gold junctions formed by tolane-type molecules with different anchoring groups (pyridyl, thiol, amine, nitrile and dihydrobenzothiophene) were studied in current-sensing force spectroscopy experiments and density functional simulations. Correlations between forces, conductances and junction geometries demonstrate that aromatic tolanes bind between electrodes as single molecules or as weakly-conductive dimers held by mechanically-weak π − π stacking. In contrast with the other anchors that form only S-Au or N-Au bonds, the pyridyl ring also forms a highly-conductive cofacial link to the gold surface. Binding of multiple molecules creates junctions with higher conductances and mechanical strengths than the single-molecule ones.

The systematic synthesis and photophysical, electrochemical and computational studies on an extended series of triphenylamine-[C[TRIPLE BOND]C-1,4-C6H2(OR)2]n-C[TRIPLE BOND]C-diphenyl-1,3,4-oxadiazole dyad molecules (the OR groups are at 2,5-positions of the para-phenylene ring and R=C6H13; n=0–5, compounds 1, 2, 3, 4 and 5, respectively) are reported. Related molecules with identical end groups, triphenylamine-C[TRIPLE BOND]C-1,4-C6H2(OR)2-C[TRIPLE BOND]C-triphenylamine (R=C6H13; 6) and diphenyl-1,3,4-oxadiazole-[C[TRIPLE BOND]C-C6H2(OR)2]2-C[TRIPLE BOND]C-diphenyl-1,3,4-oxadiazole (R=C6H13; 7) were also studied. These D–B–A 1–5, D–B–D 6 and A–B–A 7 (D=electron donor, B=bridge, A=electron acceptor) systems were synthesized using palladium-catalysed cross-coupling reactions of new p-phenyleneethynylene building blocks. Steady-state emission studies on the dyads 1–5 reveal a complicated behavior of the emission that is strongly medium dependent. In low polarity solvents the emission is characterized by a sharp high-energy peak attributed to fluorescence from a locally excited (LE) state. In more polar environments the LE state is effectively quenched by transfer into an intramolecular charge-transfer (ICT) state. The medium dependence is also observed in the quantum yields (QYs) which are high in cyclohexane and low in acetonitrile, thus also indicating charge-transfer character. Low-temperature emission spectra for 2–5 in dichloromethane and diethyl ether also reveal two distinct excited states, namely the LE state and the conventional ICT state, depending on solvent and temperature. Hybrid DFT calculations for 1–7 establish that the OPE bridge is involved in both frontier orbitals where the bridge character increases as the bridge length increases. Computed TD-DFT data on 1–5 assign the emission maxima in cyclohexane as LE transitions. Each time-resolved emission measurement on 2–7 in cyclohexane and diethyl ether reveals a wavelength dependent bi-exponential decay of the emission with a fast component in the 5–61 ps range on blue detection and a slower approximately 1 ns phase, independent of detection wavelength. The fast component is attributed to LE fluorescence and this emission component is rate limited and quenched by transfer into an ICT state. The fast LE fluorescence component varies systematically with conjugation length for the series of D–B–A dyads 2–5. An attenuation factor β of 0.15 A−1 was determined in accordance with an ICT superexchange mechanism.

The synthesis and isolation are reported of a range of terminal aryl- and heteroaryl-butadiynes (ArC⋮C−C⋮CH) 4a−h from 2-methyl-6-(aryl/heteroaryl)hexa-3,5-diyn-2-ol precursors. The stability of 4a−h in solution is concentration dependent: many of the derivatives can be stored as dilute solutions for several days or even weeks. The X-ray crystal structures have been obtained for five ArC⋮C−C⋮CH derivatives [Ar = 2-(9-fluorenonyl), 4-biphenyl, 2-pyridyl, 4-pyridyl, and 2-pyrazyl].

This paper describes the synthesis of a range of new axially-disubstituted silicon-phthalocyanines with several ester and ether derivatives as axial ligands, including phenyl, terphenyl, thienyl and pyrenyl systems. Their absorption and emission spectra are reported and fluorescence lifetimes and quantum yields are correlated with the ligand structures. The X-ray crystal structure of a new polymorph of silicon-phthalocyanine bis(3-thienyl)acetate 7 is described.

The strong solvatochromism observed for two fluorene-dibenzothiophene-S,S-dioxide oligomers in polar solvents has been investigated using steady-state and time-resolved fluorescence techniques. A low-energy absorption band, attributed to a charge-transfer (CT) state, is identified by its red shift with increasing solvent polarity. In nonpolar solvents, the emission of these conjugated luminescent oligomers shows narrow and well-resolved features, suggesting that the emission comes from a local excited state (LE), by analogy to their conjugated fluorene-based polymer counterparts. However, in polar solvents, only a featureless broad emission is observed at longer wavelengths (CT emission). A linear correlation between the energy maximum of the fluorescence emission and the solvent orientation polarizability factor Deltaf (Lippert-Mataga equation) is observed through a large range of solvents. In ethanol, below 230 K, the emission spectra of both oligomers show dual fluorescence (LE-like and CT) with the observation of a red-edge excitation effect. The stabilization of the CT emissive state by solvent polarity is accompanied/followed by structural changes to adapt the molecular structure to the new electronic density distribution. In ethanol, above 220 K, the solvent reorganization occurs on a faster time scale (less than 10 ps at 290 K), and the structural relaxation of the molecule (CT(unrelaxed) --CT(Relaxed)) can be followed independently. The magnitude of the forward rate constant, k(1)(20 degrees C) approximately 20 x 10(9) s(-1), and the reaction energy barrier, E(a) approximately 3.9 kcal mol(-1), close to the energy barrier for viscous flow in ethanol (3.54 kcal mol(-1)), show that large-amplitude molecular motions are present in the stabilization of the CT state.

Doubly and triply bridged 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) derivatives have been synthesized. Key steps are the generation and macrocyclization reactions of ex-TTF-dithiolate reagents. The X-ray crystal structures of the doubly bridged cyclophanes 15 and 16 and the triply bridged system 23 show that the saddle-like conformation of the ex-TTF framework is enhanced by the short bridges between the dithiole rings. Unlike all previous ex-TTF derivatives (which display a single quasi-reversible two-electron oxidation wave, D0 --D2+), cyclic voltammetry of the cyclophanes reveals two reversible, one-electron oxidation steps (D0 --D*+ --D2+), with differences between the half-wave potentials (E2(1/2) - E1(1/2)) of 0.22-0.26 V. The conformational changes and gain in aromaticity which drive the second oxidation process in unrestricted ex-TTF systems (including singly bridged cyclophanes) have been prevented by multiple bridging. The radical cation species gives rise to a very broad, low-energy band (lambdamax = 2175 and 2040 nm for 15 and 21, respectively), assigned to an intramolecular interaction. The steric constraints imposed by multiple bridging have become so extreme that the pi-framework of 15, 16, 21, and 23 exhibits remarkable optical and redox behavior which is not characteristic of ex-TTF systems.

Derivatives of 9-[2-(1,3-dithiol-2-ylidene)ethylidene]thioxanthene have been synthesized using Horner-Wadsworth-Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with thioxanthen-9-ylidene-acetaldehyde (5). Further reactions lead to the sterically crowded cross-conjugated "vinylogous tetrathiafulvalene" derivative 9-[2,3-bis-(4,5-dimethyl-1,3-dithiol-2-ylidene)-propylidene]thioxanthene (10). X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry, and simultaneous electrochemistry and electron paramagnetic resonance spectroscopy, combined with theoretical calculations performed at the B3LYP/6-31G(d) level, elucidate the interplay of the electronic and structural properties in these molecules. For compound 10, multistage redox behavior is observed: the overall electrochemical process can be represented by 10-->10(.+)-->10(2+)-->10(4+) with good reversibility for the 10-->10(.+)-->10(2+) transformations. At the tetracation stage there is the maximum gain in aromaticity at the dithiolium and thioxanthenium rings. Theory predicts that for 10, 10(.+), and 10(2+) the trans isomers are more stable than the cis isomers (by ca. 2-18 kJ mol(-1)), whereas for 10(4+) the cis isomer becomes more stable than the trans isomer (by ca. 25 kJ mol(-1)) [trans and cis refer to the arrangement of the two dithiole moieties with respect to the central ==C(R)--C(H)== fragment]. These data explain the detection in cyclic voltammograms of both trans and cis isomers of 10 and 10(.+) during the reduction of 10(4+) at fast scan rates (>100 mV s(-1)) when the cis-trans isomerization is not completed within the timescale of the experiment. The X-ray structure of the charge-transfer complex (CTC) of 10 with 2,4,5,7-tetranitrofluorene-9-dicyanomethylenefluorene (DTeF) [stoichiometry: 10(.+)(DTeF)(2) (.-)2 PhCl] reveals a twisted conformation of 10(.+) (driven by the bulky thioxanthene moiety) and provides a very rare example of segregated stacking of a fluorene acceptor in a CTC.

Derivatives of 9-(1,3-dithiol-2-ylidene)fluorene (9) and 9-(1,3-dithiol-2-ylidene)thioxanthene (10) have been synthesised using Horner-Wadsworth-Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with fluorenone and thioxanthen-9-one. X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry and simultaneous electrochemistry and electron paramagnetic resonance (SEEPR), combined with theoretical calculations performed at the B3P86/6-31G** level, elucidate the interplay of the electronic and structural properties in these molecules. These compounds are strong two-electron donors, and the oxidation potentials depend on the electronic structure of the oxidised state. Two, single-electron oxidations (E(1)oxE(1)ox) were observed for 9-(1,3-dithiol-2-ylidene)fluorene systems (9). In contrast, derivatives of 9-(1,3-dithiol-2-ylidene)thioxanthene (10) display the unusual phenomenon of inverted potentials (E(1)oxE(1)ox) resulting in a single, two-electron oxidation process. The latter is due to the aromatic structure of the thioxanthenium cation (formed on the loss of a second electron), which stabilises the dication state (10(2+)) compared with the radical cation. This contrasts with the nonaromatic structure of the fluorenium cation of system 9. The two-electron oxidation wave in the thioxanthene derivatives is split into two separate one-electron waves in the corresponding sulfoxide and sulfone derivatives 27-29 owing to destabilisation of the dication state.

The first pi-extended tetrathiafulvalene (exTTF) dimer in which the two exTTF units are covalently connected by 1,3-dithiole rings has been obtained in a multistep synthetic procedure involving the Ullmann cross-coupling reaction by using copper(I) thiophene-2-carboxylate (CuTC). The electronic spectrum reveals a significant electronic interaction between the exTTF units. The electrochemical study carried out by cyclic voltammetry in solution and in thin-layer conditions, and the electrochemical simulation and spectroelectrochemical (SEC) measurements confirm the electronic communication and show that the oxidation of dimer 14 occurs as two consecutive 2 e(-) processes D(0)-D(0)-->D(2+)-D(0)-->D(2+)-D(2+). Theoretical calculations, performed at the B3P86/6-31G* level, confirm the experimental findings and predict that 14(2+) exists as a delocalized D(.+)-D(.+) species in the gas phase and as a localized D(2+)-D(0) species in solution (CH(3)CN or CH(2)Cl(2)). Oxidation of 14(2+) forms the tetracation 14(4+) which is constituted by two aromatic anthracene units bearing four aromatic, almost orthogonal 1,3-dithiolium cations.

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.

[structure: see text] The synthesis of a new series of rigid-rod aryleneethynylene derivatives of up to ca. 10 nm molecular length (compounds 16 and 17) is reported using iterative Pd-mediated Sonogashira coupling methodology combined with regioselective removal of the different protecting groups (namely, trimethylsilyl and 2-hydroxyprop-2-yl groups) from the terminal alkyne units. Additionally, the TMS-acetylene unit has been cleanly deprotected to afford a terminal alkyne in the presence of a cyanoethylsulfanyl group. Some of these molecular wires are functionalized with terminal protected thiophenol units for attachment to metal surfaces (compounds 16 and 17). Internal electron-acceptor units have been incorporated into their structures, namely, 9-[di(4-pyridyl)methylene]fluorene (compound 17) or fluorenone (compounds 19-22). Optical absorption and photoluminescence spectra reveal a red shift in the value of lambda(max) with increasing molecular length, which approaches saturation at an effective conjugation length of ca. 15-20 pi-units in the molecules, where each phenyl ring or a triple bond is counted as one pi-unit.

The syntheses of N-hexylcarbazol-2-yl- and -3-yl-boron- ic acids (1 and 2) are described on a ca. 7 g scale, starting from com- mercially available 2,5-dibromonitrobenzene (4) and carbazole (11), respectively. Compounds 1 and 2 underwent efficient palladi- um-catalyzed cross-coupling reactions under Suzuki-Miyaura con- ditions to yield products 17, 18 and 20. Compound 18 reacted with IrCl3 to give the tris-cyclometalated (pyridin-2-yl)carbazole iridi- um(III) complex 21, the X-ray crystal structure of which is reported.

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.

The housefly, Musca domestica L. (Diptera: Muscidae), is recognized as an important factor in the dissemination of various infectious diseases such as cholera, shigellosis, and salmonellosis. They can also serve as a cross-contamination vector for other foodborne pathogens. However, the potential for bacterial transfer by houseflies has been demonstrated in a qualitative rather than quantitative manner. In this study, the numbers of bacteria a housefly can carry on its body and transfer to a clean surface after exposure to a sugar-milk aqueous solution, steak, and potato salad contaminated with a fluorescent gene Escherichia coli (8 log10 CFU/ml) were determined. In the first series of experiments to quantify bacterial numbers on the flies, about 40-60 flies were transferred into a sterile cage, exposed to the food for 30 min, the flies immobilized and the attached E. coli on each fly enumerated. Detectable E. coli (>1.7 log10 CFU/fly) were found on 43% (29/67), 53% (23/43), and 62% (32/52) of the flies in the cages with sugar/milk, steak, and potato salad, respectively. For the positive flies, the geometric mean carriage (log10 CFU/fly) was 2.93+/-1.24 for sugar-milk, 3.77+/-1.28 for steak, and 2.25+/-0.64 for the potato salad. In the second series of experiments, the transfer of bacteria by individual flies from contaminated food to the inner surface of a sterile jar per each landing was determined. E. coli transferred from the sugar-milk was 3.5+/-0.7 log10 CFU/fly-landing, 3.9+/-0.7 for steak and 2.61+/-1.16 for the potato salad. From the initial contamination levels of bacteria and the number of transferred bacteria, it can be calculated that flies contaminate clean surfaces with approximately 0.1 mg of food per landing.

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.