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Here two D–A3 regioisomers, comprising three dibenzothiophene-S,S-dioxide acceptor units attached to a central triazatruxene core, are studied. Both molecules show thermally activated delayed fluorescence (TADF), however, the efficiency of the TADF mechanism is strongly affected by the D–A substitution position. The meta- substituted emitter (1 b) shows a slightly higher-lying singlet charge transfer state and a lower-lying triplet state than that observed in the para- substituted emitter (1 a), resulting in a larger singlet–triplet splitting (ΔEST) of 0.28 eV compared to only 0.01 eV found in 1 a. As expected, this ΔEST difference strongly impacts the reverse intersystem crossing (rISC) rates and the para- isomer 1 a exhibits a much faster delayed fluorescence emission. Calculations show that the triplet energy difference between the two isomers is due to steric hindrance variances along the donor–acceptor rotation axis in these molecules: as 1 b is less restricted, rotation of its acceptor unit leads to a lower T1 energy, further away from the region of high density of states (the region where larger vibronic coupling is found, favouring rISC). Therefore, our results show how the substitution pattern has a marked effect on triplet state energies and character, verifying the key structural designs for highly efficient TADF materials.

A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho‐alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene‐S,S‐dioxide) and a bis(thioxanthene‐S,S‐dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para‐ vs. meta‐ vs. broken conjugation, and electron‐rich vs. electron‐poor heterocycles impact the HOMO–LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (E T) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in E T of 0.24 eV in the different media—sufficiently large to “make‐or‐break” an OLED device—with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower E T values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high E T materials and controlling their HOMO and LUMO energies., A new series of high E T heterocyclic dimers has been synthesized with large dihedral angles enforced by steric hindrance. A meta‐conjugated carbazole dimer displays the highest E T of 3.07 eV in dilute polymer film, however in a neat film this falls to 2.83 eV. Similar variation is observed across the series. This work highlights that to reliably estimate host/guest compatibility, E T determined from phosphorescence of neat films must be reported for new host materials. The currently accepted practice of reporting values from frozen solution or polymer films is no substitute.

Two asymmetric “half-dendronized” and “half-dendronized-half-encapsulated” TADF emitters eliminate degenerate excited states, assuring a solely thermal equilibrium route for an effective spin-flip process. AEE properties can minimize the exciton quenching. The isolated encapsulating tricarbazole unit protects the TADF unit, reducing nonradiative decay. Non-doped OLEDs with a remarkably high EQEmax of 24.0 % and low roll-off are achieved. The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully-conjugated or fully-nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical “half-dendronized” and “half-dendronized-half-encapsulated” emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge-transfer state, assuring a solely thermal equilibrium route for an effective spin-flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non-doped solution-processed devices reach a high external quantum efficiency (EQEmax) of 24.0 % (65.9 cd A−1, 59.2 lm W−1) with CIE coordinates of (0.24, 0.45) with a low efficiency roll-off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m−2.

This article reports new tris‐cyclometalated Ir complexes containing mixed‐C^N ligands, (C^N1)2Ir(C^N2), which are a rarely explored class of Ir(III) complexes. Two new mixed 2‐phenylpyridine (ppy) / 4‐methyl‐2,5‐diphenylpyridine (mdp) complexes (ppy)2Ir(mdp) and (ppy)Ir(mdp)2 have been synthesized and their optoelectronic properties have been systematically characterized. Photoluminescence quantum yield values are 0.76‐0.85; excited state lifetimes are 0.07‐0.11 μs. Phosphorescent organic light emitting devices (PhOLEDs) based on these emissive complexes in a very simple device architecture reproducibly showed slightly higher external quantum efficiency (EQE) and power efficiency (PE) values compared with devices using the analogous conventional homoleptic Ir complexes Ir(ppy)3 and Ir(mdp)3, and the heteroleptic complexes (ppy)2Ir(acac) and (mdp)2Ir(acac). The new complexes (ppy)2Ir(mdp) 3 and (ppy)Ir(mdp)2 4 give PhOLEDs with EQEmax and PEmax values of 26.7 and 26.0% / 94.7 and 94.1 lm W−1, respectively, and very high values are retained at the practical luminances of 100 and 1000 cd m−2. The values for (ppy)2Ir(mdp) are 26.3% and 73.6 lm W−1 (at 100 cd m−2) and 24.6% and 53.5 lm W−1 (at 1000 cd m−2). These efficiencies are comparable with the highest reported values of PhOLEDs using conventional Ir(III) emitters in more complicated device structures. Mixed C^N ligand systems are, therefore, a viable strategy for developing new efficient phosphorescent emitters.

Objectives To investigate the effect of client complaints on small animal veterinary internists' welfare, job satisfaction and medical practices. Materials and methods Cross-sectional anonymous survey study. Between February 1 and March 31, 2017, a web-based questionnaire was made available through the American College Veterinary Internal Medicine sub-specialty Small Animal Internal Medicine E-mail List Serve. Results A total of 92 completed surveys were available for review. Fifty-nine (64∙1%) respondents received a client complaint during the previous 6 months with cost of care the most common reason (53∙3%). Eighty-nine (96∙7%) respondents worry about client complaints being made against them with 33 (35∙8%) stating they worry "most of the time" or "all of the time." Thirty-two (34∙8%) reported being verbally assaulted by a client in the previous 6 months and 27 (29∙4%) reported being threatened with litigation during the previous 6 months. Sixty-six (71∙7%) have reported changing the way they practice medicine to avoid a client complaint and 40 (43∙5%) have considered changing their career because of complaints made against them. Clinical relevance Client complaints are a frequent problem among small animal veterinary internists that have detrimental effects on job satisfaction, psychological distress and medical practices.

We studied the single-molecule conductance through an acid oxidant triggered phenothiazine (PTZ-) based radical junction using the mechanically controllable break junction technique. The electrical conductance of the radical state was enhanced by up to 200 times compared to the neutral state, with high stability lasting for at least two months and high junction formation probability at room-temperature. Theoretical studies revealed that the conductance increase is due to a significant decrease of the HOMO–LUMO gap and also the enhanced transmission close to the HOMO orbital when the radical forms. The large conductance enhancement induced by the formation of the stable PTZ radical molecule will lead to promising applications in single-molecule electronics and spintronics.

The photophysics of thermally activated delayed fluorescence (TADF) in phenothiazine-dibenzothiophene-S,S-dioxide (PTZ-DBTO2) molecule is investigated in detail. First, it is shown that the proximity of local triplet excited states (3LE), e.g., 3D or 3A, above or below the DA charge transfer states (CT) is crucial for the efficiency of the TADF mechanism in PTZ-DBTO2. This TADF emitter is then used as a monomer unit to design polymer materials with efficient TADF. The reverse intersystem crossing mechanism (RISC) that supports TADF is able to compete with internal conversion and triplet–triplet annihilation (TTA) in the polymer chains and generates efficient TADF emission in the polymer pristine films. Prototype devices with PTZ-DBTO2 dispersed in 4,4′-bis(N-carbazolyl)-2,2′-biphenyl (CBP) host give excellent performance with EQE of ≈22% at low luminance (

Although persistent room‐temperature phosphorescence (RTP) emission has been observed for a few pure crystalline organic molecules, there is no consistent mechanism and no universal design strategy for organic persistent RTP (pRTP) materials. A new mechanism for pRTP is presented, based on combining the advantages of different excited‐state configurations in coupled intermolecular units, which may be applicable to a wide range of organic molecules. By following this mechanism, we have developed a successful design strategy to obtain bright pRTP by utilizing a heavy halogen atom to further increase the intersystem crossing rate of the coupled units. RTP with a remarkably long lifetime of 0.28 s and a very high quantum efficiency of 5 % was thus obtained under ambient conditions. This strategy represents an important step in the understanding of organic pRTP emission.

Genetic counseling for prenatal diagnosis of autosomal trisomy is complex because of the uncertainty of outcome, which is important for management decisions. Compilation of cases of prenatally diagnosed autosomal trisomies in amniocytes has been done previously in an attempt to elucidate the clinical phenotype of these pregnancies. It has been greater than a decade since these studies were completed. To update this work, we reviewed cases reported in the literature since that time. These cases are correlated with the prior reports to increase knowledge about outcomes and to hopefully improve the data available for genetic counseling. The risk of abnormal outcome can be summarized as: very high risk (>60%) for 47,+2/46; 47,+9/46; 47,+16/46; 47,+20/46; and 47,+22/46; high risk (40–59%) for 47,+5/46; 47,+14/46; and 47,+15/46; moderately high risk (20–39%) for 47,+7/46 47,+12/46; and 47,+17/46; moderate risk (up to 19%) for 47,+6/46 and 47,+8/46, and none were low risk. 47,+6/46 was originally indeterminate, 47,+7/46 was originally moderate risk, 47,+9/46 was originally high risk, and 47,+17/46 was originally low risk. © 2015 John Wiley & Sons, Ltd.

Easily reversible aqueous dispersion/precipitation of multiwalled carbon nanotubes (MWNTs) has been demonstrated using small-molecule non-ionic pyrene-based surfactants, which exhibit lower critical solution temperature (LCST) phase behaviour. The MWNTs are dispersed by means of non-covalent interactions. The dispersibility can be switched "off" (i.e., MWNTs precipitated) upon heating and switched "on" (i.e., MWNTs re-dispersed) upon cooling and merely swirling the sample at room temperature, that is, under very mild conditions. This effect is also observed under high ionic strength conditions with NaCl in the aqueous phase.

Two phosphorescent dinuclear iridium(III) diastereomers (ΛΔ/ΔΛ) and (ΛΛ/ΔΔ) are readily separated by making use of their different solubilities in hot hexane. The bridging diarylhydrazide ligand plays an important role in the electrochemistry and photophysics of the complexes. Organic light-emitting devices (OLEDs) that use these complexes as the green-emissive dopants in solution-processable single-active-layer architectures feature electroluminescence efficiencies that are remarkably high for dinuclear metal complexes, achieving maximum values of 37 cd A(-1), 14 lm W(-1), and 11% external quantum efficiency.

Two phosphorescent iridium complexes with bipolar transporting ability, namely FPPCA (500 nm) and BZQPG (600 nm), are synthesized and employed as an ideal host-guest system for phosphorescent organic light emitting diodes (PHOLEDs).The devices give very high-efficiency orange-red emission from BZQPG with maximum external quantum efficiency (EQE or ηext) of >27% and maximum power efficiency (PE or ηp) of >75 lm/W, and maintain high levels of 26% and 55 lm/W, 25% and 40 lm/W at high luminance of 1000 and 5000 cd m−2, respectively, within a range of 8–15 wt% of BZQPG. The realization of such high and stable EL performance results from the coexistence of two parallel paths: i) effective energy transfer from host (FPPCA) to guest (BZQPG) and ii) direct exciton formation on the BZQPG emitter, which can alternately dominate the electrophosphorescent emission. This all-phosphor doping system removes the charge-injection barrier from the charge-transport process to the emissive layer (EML) due to the inherent narrow Eg of both phosphors. Therefore, this ideal host–guest system represents a new design to produce PHOLEDs with high efficiency and low efficiency roll-off using a simple device configuration.

New emitters that can harvest both singlet and triplet excited states to give 100% internal conversion of charge into light, are required to replace Ir based phosphors in organic light emitting diodes (OLEDs). Molecules that have a charge transfer (CT) excited state can potentially achieve this through the mechanism of thermally activated delayed fluorescence (TADF). Here, it is shown that a D–A charge transfer molecule in the solid state, can emit not only via an intramolecular charge transfer (ICT) excited state, but also from exciplex states, formed between the molecule and the host material. OLEDs based on a previously studied D–A–D molecule in a host TAPC achieves >14% external electroluminescence yield and shows nearly 100% efficient triplet harvesting. In these devices, it is unambiguously established that the triplet states are harvested via TADF, but more interestingly, these results are found to be independent of whether the emitter is the ICT state or the D–A–D/host exciplex.

The syntheses of two new heteroleptic cationic iridium complexes containing 2,6-diphenylpyridine (Hdppy) and 2,4,6-triphenylpyridine (Htppy) as the cyclometalated ligands, namely, [Ir(dppy)2phen]PF6 (1, phen = 1,10-phenanthroline) and [Ir(tppy)2phen]PF6 (2), are described. The X-ray crystal structure of 2 reveals a distorted octahedral geometry around the Ir center and close intramolecular face-to-face π–π stacking interactions between the pendant phenyl rings at the 2-position of the cyclometalated ligands and the NN ancillary ligand. This represents a new π–π stacking mode in charged Ir complexes. Complexes 1 and 2 are green photoemitters: their photophysical and electrochemical properties are interpreted with the assistance of density functional theory (DFT) calculations. These calculations also establish that the observed intramolecular interactions cannot effectively prevent the lengthening of the Ir–N bonds of the complexes in their metal-centered (3MC) states. Complexes 1 and 2 do not emit light in light-emitting electrochemical cells (LECs) under conditions in which the model compound [Ir(ppy)2phen]PF6 (3) emits strongly. This is explained by degradation reactions of the 3MC state of 1 and 2 under the applied bias during LEC operation facilitated by the enhanced distortions in the geometry of the complexes. These observations have important implications for the future design of complexes for LEC applications.

We report on measurements on molecular wires in single-molecule junctions. The target is to identify vibrational signatures in the differential conductance spectra, which cannot be resolved for most molecular wires in the resonant transport regime. For the given molecules, we find indeed vibrational sidepeaks, which can be assigned to the longitudinal modes of the string-like central motif of the molecule by comparison with density functional theory. These data corroborate that oligoyne wires are ideally suited for characterizing vibrational sidepeaks. A current increase as a consequence of vibrational decoherence observed for thiols is, however, not found due to the pyridine anchor group chosen in the present molecules.

The wire-like properties of four S-(4-{2-[4-(2-phenylethynyl)phenyl]ethynyl}phenyl) thioacetate derivatives, PhC≡CC(6)H(4)C≡CC(6)H(4)SAc (1), H(2)NC(6)H(4)C≡CC(6)H(4)C≡CC(6)H(4)SAc (2), PhC≡CC(6)H(2)(OMe)(2)C≡CC(6)H(4)SAc (3) and AcSC(6)H(4)C≡CC(6)H(4)C≡CC(6)H(4)SAc (4) (Figure 1), all of which possess a high degree of conjugation along the oligo(phenyleneethynylene) (OPE) backbone, were investigated as self-assembled monolayers (SAMs) on gold and platinum electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The redox probe [Fe(CN)(6)](4)(-) was used in both the CV and impedance experiments. The results indicate that the thiolates derived from thioacetate-protected precursor molecules 1 and 2 form well-ordered monolayers on a gold electrode, whereas SAMs derived from 3 and 4 exhibit randomly distributed pinholes. The electron tunnelling resistance and fractional coverage of SAMs of all four compounds were examined using electron tunnelling theory. The analysis of the results reveal that the well-ordered SAMs of 1 and 2 exhibit higher charge-transfer resistance in comparison to the defect-ridden SAMs of 3 and 4. The additional steric bulk offered by the methoxy groups in 3 is likely to prevent efficient packing within the SAM, leading to a microelectrode behaviour, when assembled on a gold electrode surface. The protected dithiol derivative 4 probably binds to the surface through both terminal groups which prevents dense packing and leads to the formation of a monolayer with randomly distributed pinholes. Atomic force microscopy (AFM) was used to examine the morphology of the monolayers, and height images gave root-mean-square (RMS) roughness's which are in agreement with the proposed SAM structures.

Random copolymers of poly(9,9-di-n-octylfluorene) (PF8) incorporating 0, 8, 12, 15, and 20% dibenzothiophene (DBT), and copolymers with 2, 5, 8, 12, and 15% dibenzothiophene-S,S-dioxide (S-unit) were synthesised. Absorption and emission spectra of thin films indicate that the DBT system shows a linear decrease of toluene vapour induced β phase with increasing DBT content to a 20% cutoff, whilst in the S-unit copolymers the β phase is present up to 12% co-monomer content, and at 15% the characteristic absorption peak is absent or masked. These results demonstrate the limits, in thin films, at which the β phase can be formed in widely used PF8 copolymer systems for device applications and clearly show that it is practical to use copolymers having electron or hole transport units in the polyfluorene backbone and still be able to form efficient β phase emission sites.

A new family of highly soluble electrophosphorescent dopants based on a series of tris-cyclometalated iridium(III) complexes (1-4) of 2-(carbazol-3-yl)-4/5-R-pyridine ligands with varying molecular dipole strengths have been synthesized. Highly efficient, solution-processed, single-layer, electrophosphorescent diodes utilizing these complexes have been prepared and characterized. The high triplet energy poly(9-vinylcarbazole) PVK is used as a host polymer doped with 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) for electron transport. Devices with a current efficiency of 40 cd A(-1) corresponding to an EQE of 12% can thus be achieved. The effect of the type and position of the substituent (electron-withdrawing group (CF3) and electron-donating group (OMe)) on the molecular dipole moment of the complexes has been investigated. A correlation between the absorption strength of the singlet metal-to-ligand charge-transfer ((MLCT)-M-1) transition and the luminance spectral red shift as a function of solvent polarity is observed. The strength of the transition dipole moments for complexes 1-4 has also been obtained from TD-DFT computations, and is found to be consistent with the observed molecular dipole moments of these complexes. The relatively long lifetime of the excitons of the phosphorescence (microseconds) compared to the charge-carrier scattering time (less than nanoseconds), allows the transition dipole moment to be considered as a "quasi permanent dipole". Therefore, the carrier mobility is sufficiently affected by the long-lived transition dipole moments of the phosphorescent molecules, which are randomly oriented in the medium. The dopant dipoles cause positional and energetic disorder because of the locally modified polarization energy. Furthermore, the electron-withdrawing group CF3 induces strong carrier dispersion that enhances the electron mobility. Therefore, the strong transition dipole moment in complexes 3 and 4 perturbs both electron and hole mobilities, yielding a reduction in exciton formation and an increase in the device dark current, thereby decreasing the device efficiency. UK Research & Innovation (UKRI) Engineering & Physical Sciences Research Council (EPSRC) (EP/I013695/1)

The singlet oxygen (1O2) generation ability of a photosensitizer (PS) is pivotal for photodynamic therapy (PDT). Transition metal complexes are effective PSs, owing to their high 1O2 generation ability. However, non‐negligible cellular toxicity, poor biocompatibility, and easy aggregation in water limit their biomedical applications. In this work, a series of red‐emitting aggregation‐induced emission (AIE) Ir(III) complexes containing different numbers of Ir centers (mono‐, di‐, and trinuclear) and the corresponding nanoparticles (NPs) AIE‐NPs, are designed and synthesized. The increase of 1O2 generation ability is in line with the increasing number of Ir centers. Compared with the pure Ir(III) complexes, the corresponding NPs offer multiple advantages: (i) brighter emission; (ii) higher phosphorescence quantum yields; (iii) longer excited lifetime; (iv) higher 1O2 generation ability; (v) better biocompatibility; and (vi) superior cellular uptake. Both in vitro and in vivo experiments corroborate that AIE‐NPs with three iridium centers possess potent cytotoxicity toward cancer cells and effective inhibition of tumor growth. To the best of knowledge, this work is the first example of NPs of multinuclear AIE Ir(III) complexes as PSs for enhanced PDT. This study offers a new method to improve the efficiency of PSs for clinical cancer treatments.

A series of 3,7-bis(9,9-di-n-hexylfluoren-2-yl)-N-aryl- phenothiazine-S,S-dioxide trimers and (9,9-di-n-octylfluorene- 2,7-diyl-co-N-arylphenothiazine-S,S-dioxide) co-polymers, with varying ratios of phenothiazine-S,S-dioxide units, have been prepared in good yields by palladium-catalyzed cross-coupling reactions. The materials are deep blue emitters and show no solvatochromism or evidence for an intramolecular charge- transfer state. The photoluminescence quantum yields of the trimers are UPL 15-30% in solution and 14-25% in films. The polymers demonstrated very high values in solution (UPL 74- 84%) and UPL values in films of 28-47%. The estimated HOMO energy levels are between � 5.64 and � 5.62 eV for the poly- mers with 15% incorporation of the phenothiazine-S,S-dioxide units. An analogous N-arylphenothiazine co-polymer shows significantly red shifted absorption and emission. Solution electrochemical data and density functional theory calculations are also presented. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1129-1137, 2011

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 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.

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)

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)

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)

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)

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.

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.

The syntheses of a series of novel tetrathiafulvalene derivatives substituted with four side-chains terminating in hydrophilic amidoalcohol (arborol) groups are reported, for example the tetrathiafulvalene derivative 15. Some of these arborol derivatives formed thin films by spin-coating from methanol solution onto solid supports such as glass, ITO-coated glass and gold. The quality of the films improved markedly with an increasing number of alcohol substituents at the periphery of the molecule. Optical absorption spectroscopy showed that oxidative doping of these films could be achieved chemically and electrochemically. The observation of low-energy bands in the UV/Vis absorption spectra (λmax = 820 nm tailing to ca. 1300 nm) and the moderate levels of conductivity (σrt ≈ 10−4 S cm−1) in these doped films strongly suggest that a significant degree of supramolecular order is present, with π-π stacking of the TTF cores. To the best of our knowledge this is the first time that semiconducting behaviour has been achieved in molecular arborol systems that possess an electroactive core unit. This work offers the prospect of using spin-coated films of TTF-arborols as semiconducting charge-transport layers in optoelectronic devices. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Novel R3TTF-sigma-A compounds 14, 16 and 19 (R3TTF = trial-kyltetrathiafulvalene, sigma = saturated spacer, A = polynitrofluoren-9-dicyano-methylene acceptor) incorporating very strong donor and acceptor moieties have been synthesized by condensation of the corresponding R3TTF-sigma-fluoren-9-one diads with malononitrile. Reversible five-step amphoteric redox behavior has been observed with an extremely low HOMO-LUMO gap (approximate to 0.3 eV). For compound 14 a strong EPR signal is observed in the solid state, ascribed to intermolecular complexation: a less intense signal is seen in solution, corresponding to ca. 2% of the molecules existing in a radical form at room temperature. Intramolecular charge transfer in diads 14 and 16 is manifested in strong absorption bands in the near-IR region of their electronic spectra. Spectroelectrochemical data reveal marked electrochromic behavior in the visible and near-IR region of both compounds. The first X-ray crystal structure of a fluorene radical-anion salt is reported, namely the copper salt of 2,4,5,7-tetranitro-9-dicyanomethylenefluorene (1:1 stoichiometry).

Thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) have drawn tremendous interest and have been extensively studied because of harvesting both triplet and singlet excitons without heavy metals. However, single white-light-emitting polymers are currently limited and few strategies exist to design these materials. Herein, a new strategy is proposed to develop the polymers with tunable emission colors by combining fluorescence and TADF based on aggregation-enhanced emission (AEE) characteristics. The polymers containing different ratios of pendant 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide units with yellow TADF emission and dibenzothiophene units with blue fluorophor emission, which display both TADF and AEE characteristics, are synthesized successfully. Among them, the emission color of P3 in different tetrahydrofuran/water mixtures changes from greenish-blue to white or yellow. Moreover, P3 displays white emission in the solid state dispersing by poly(methyl methacrylate). In addition, electroluminescent device of P3 achieve white light emission with high color rending indexes (CRI) and low turn-on voltages (V on ). P3 OLEDs show two-color warm-white emission with high CRI of 77, low V on of 2.9 V, CEmax of 23.0 cd A−1, PEmax of 32.8 lm W−1, external quantum efficiency (EQE)max of 10.4% with Commission Internationale de l'Eclairage coordinates of (0.37, 0.38) at 5 V. Moreover, EQE of 2.6%, CE of 5.7 cd/A, PE of 4.7 lm W−1 at 100 cd m−2 are obtained. To the best of our knowledge, this work reports the first example of warm-white TADF polymer OLEDs.

Electron donor−π−acceptor chromophores 5, 9, 11, 18−20, 21, 22, 27, 28a, 28c, 31, 32, 34−36, 38a−c, 41a, 41c, and 42 have been synthesised. The donor units are 1,3-dithiole and ferrocene; conjugated ethylenic, phenyl, phenylenevinylene, thienyl, bithienyl, terthienyl, or thienylenevinylene linkers act as a central π-electron relay unit, and dicyanomethylene and polynitrofluorene groups as the acceptor unit. The electronic absorption spectra display a broad low-energy intramolecular charge transfer band in the visible region (500−700 nm) the energy (hνICT ≈ 1.7−2.5 eV) and intensity (ϵ ≈ 5000−50000 M−1cm−1) of which depend substantially on the nature of both D and A moieties and on the structure of the linker unit. Nonlinear optical properties have been evaluated using the EFISH technique: the highest μβ(0) values are observed for 38b [(900±300)×10−48 esu] and 42 [(1800±300)×10−48 esu] establishing that polynitrofluorene is a promising acceptor terminal moiety in this context. The molecular and electronic structures of 49 and 50 have been calculated by the RHF/6-31G(d)//RHF/6-31G(d) ab initio method. The HOMO is located mostly in the 1,3-dithiolium ring, and the LUMO mostly at the dicyanomethylene fragment (and the phenyl ring of 50) although the electronic population at C2 of the 1,3-dithiolium rings is also considerable. The X-ray crystal structures of 9, 18 and 27 are reported. In all three structures the conjugated π-systems are effectively planar with extensive π-electron delocalisation between the donor and acceptor moieties. The planar conformation of 18 gives rise to a close intramolecular S···S contact of 3.095(3) A between the dithiole and thiophene units.

We have synthesised new conjugated donor-π-acceptor (D-π-A) chromophores 7, 9, and 12−15 in which monosubstituted tetrathiafulvalene (TTF) and trimethyl-TTF units are the donor moieties, connected by ethylenic bridges to electron-deficient benzene derivatives as the acceptor moieties. These compounds display a broad intramolecular charge transfer (ICT) band in their solution UV/Vis spectra at λmax = ca. 500 nm. The second order nonlinear optical (NLO) properties of these derivatives have been studied using the EFISH technique and calculated by semiempirical and ab initio theoretical methods. The effect of methyl substituents in the TTF moiety and the nature of the conjugated bridge are discussed. Analysis of the bond lengths obtained by an X-ray diffraction study of compound 9 reveal ICT in the solid state.

The synthesis of O S -crown annelated derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene using the novel Horner-Wadsworth-Emmons reagent 7 is reported. The bis- and mono-crown systems 9 and 12 function as efficient ligands in the voltammetric and UV/Vis spectroscopic recognition of Na and Ag . Solution electrochemical studies reveal that metal complexation to the crown unit(s) leads to a significant positive shift in the potential of the first, two-electron oxidation wave of 9 and 12 [maximum shift E = 115 mV for 9 in the presence of Ag (ca. 10 molar equivalents)]. Considerably smaller shifts (< 30 mV) were observed for complexation of Li , K and Ba . UV/Vis spectrophotometric studies of metal binding (Na and Ag ) to 9 are consistent with the simultaneous formation of 1:1 and 1:2 complexes. The X-ray crystal structures of compounds 10 and 12-CH Cl are reported. The anthracenediylidene moiety of 12 is U-shaped due to the boat conformation of the central (quinodimethane) ring and folding of both 1,3-dithiole rings, providing an overall saddle conformation. The folding in 10 is reduced as steric crowding is relieved by removal of one of the 1,3-dithiole units. © Wiley-VCH Verlag GmbH, 2001. 4 2 1 2 2 + + ox + + + 2+ + +

Flash photolysis of bis[4.5-di(methylsulfanyl) 1,3-dithiol-2-ylidene]-9,10(-dihydroanthracene (1) in chloroform leads to formation of the transient radical cation species 1.+ which has a diagnostic broad absorption band at lambdamax approximately 650 nm. This band decays to half its original intensity over a period of about 80 micros. Species 1.+ has also been characterised by resonance Raman spectroscopy. In degassed solution 1.+ disproportionates to give the dication 1(2+), whereas in aerated solutions the photodegradation product is the 10-[4,5-di(methylsulfanyl) 1,3-dithiol-2-ylidene]anthracene-9(10 H)one (2). The dication 1(2+) has been characterised by a spectroelectrochemical study [lambdamax (CH2Cl2) = 377, 392, 419, 479 nm] and by an X-ray crystal structure of the salt 1(2-) (ClO4)2, which was obtained by electrocrystallisation. The planar anthracene and 1,3-dithiolium rings in the dication form a dihedral angle of 77.2 degrees; this conformation is strikingly different from the saddle-shaped structure of neutral 1 reported previously.

The syntheses are reported of the title polymeric alkoxyPBD derivative 5 and the dipyridyl analogue 12 using Suzuki coupling reactions of 1,4-dialkoxybenzene-2,5-diboronic acid with 2,5-bis(4-bromophenyl)-1,3,5-oxadiazole, and its dipyridyl analogue, respectively. Thermal gravimetric analysis shows that polymers 5 and 12 are stable up to 370 C and 334 C, respectively. Films of polymer 5 spun from chloroform solution show an absorption at kmax = 367 nm, and a weaker band at 312 nm, and strong blue photoluminescence at kmax = 444 nm. The photoluminescence quantum yield (PLQY) was found to be 27 ‐ 3 %. For polymer 12, the absorption spectra reveal bands of equal intensity at kmax = 374 and 312 nm, with PL at kmax = 475 nm. Device studies using polymer 12 were hampered by its instability under illumination and/or electrical excitation. Polymer 5 is stable under these conditions and acts as an efficient electron-transporting/hole-blocking layer. For devices of configuration ITO/PEDOT/ MEH-PPV/polymer 5/Al an external quantum efficiency of 0.26 % and brightness of 800 cd/m 2 was readily achieved: orange emission was observed, identical to the MEH-PPV electroluminescence.