Search

The synthetic methodology to covalently link donors to form cyclophane-based thermally activated delayed fluorescence (TADF) molecules is presented. These are the first reported examples of TADF cyclophanes with “electronically innocent” bridges between the donor units. Using a phenothiazine-dibenzothiophene-S,S-dioxide donor–acceptor–donor (D–A–D) system, the two phenothiazine (PTZ) donor units were linked by three different strategies: (i) ester condensation, (ii) ether synthesis, and (iii) ring closing metathesis. Detailed X-ray crystallographic, photophysical and computational analyses show that the cyclophane molecular architecture alters the conformational distribution of the PTZ units, while retaining a certain degree of rotational freedom of the intersegmental D–A axes that is crucial for efficient TADF. Despite their different structures, the cyclophanes and their nonbridged precursors have similar photophysical properties since they emit through similar excited states resulting from the presence of the equatorial conformation of their PTZ donor segments. In particular, the axial–axial conformations, known to be detrimental to the TADF process, are suppressed by linking the PTZ units to form a cyclophane. The work establishes a versatile linking strategy that could be used in further functionalization while retaining the excellent photophysical properties of the parent D–A–D system.

There are notably few literature reports of electron donor-acceptor oligoynes although they offer unique opportunities for studying charge transport through ‘all-carbon’ molecular bridges. In this context, the current study focuses on a series of carbazole–(C≡C)n-2,5-diphenyl-1,3,4-oxadiazoles (n = 1-4) as conjugated π-systems, in general, and explores their photophysical properties, in particular. Contrary to the behavior of typical electron donor-acceptor systems, for these oligoynes the rates of charge recombination after photoexcitation increase with increasing electron donoracceptor distance. To elucidate this unusual performance, detailed photophysical and time-dependent density functional theory investigations were conducted. Significant delocalization of the electron density along the bridge indicates that the bridging states come into resonance with either the electron donor or acceptor, thereby accelerating the charge transfer. Moreover, the calculated bond lengths reveal a reduction in bond length alternation upon photoexcitation, indicating significant cumulenic character of the bridge in the excited state. In short, strong vibronic coupling between the electrondonating N-arylcarbazoles and the electron-accepting 1,3,4-oxadiazoles accelerates the charge recombination as the oligoyne becomes longer.

We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) states. The key requirement for the efficient TADF emitters is to achieve a very small CT-local triplet state energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electrons on the D and A in the CT state. In addition, the possibility of aggregation-induced TADF (AI-TADF) is examined and shown to be a manifestation of solvatochromism in these particular molecules.

This study reports two novel D–A–D molecules, 2,7-bis(phenothiazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPT-TXO2) and 2,7-bis(1-methylphenothiazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DMePT-TXO2), where the latter differs by only a methyl group incorporated on each of the donor units. DMePT-TXO2 in solution and in solid state shows dual charge-transfer (CT) emission. The CT states come from two distinctive conformations between the D and A units. Experiments show that the emission contribution of each state can be controlled by the polarity of the environment and by the excitation energy. Also, how the different conformers can be used to control the TADF mechanism is analyzed in detail. These results are important as they give a more in-depth understanding about the relation between molecular conformation and the TADF mechanism, thereby facilitating the design of new TADF molecules.

The new homoleptic tris-cyclometalated [Ir(C^N)(3)] complexes mer-8, fac-8, and fac-9 incorporating γ-carboline ligands are reported. Reaction of 3-(2,4-difluorophenyl)-5-(2-ethylhexyl)-pyrido[4,3-b]indole 6 with iridium(III) chloride under standard cyclometalating conditions gave the homoleptic complex mer-8 in 63% yield. The X-ray crystal structure of mer-8 is described. The Ir-C and Ir-N bonds show the expected bond length alternations for the differing trans influence of phenyl and pyridyl ligands. mer-8 quantitatively isomerized to fac-8 upon irradiation with UV light. However, heating mer-8 at 290 °C in glycerol led to an unusual regioselective loss of one fluorine atom from each of the ligands, yielding fac-9 in 58% yield. fac-8 is thermally very stable: no decomposition was observed when fac-8 was heated in glycerol at 290 °C for 48 h. The γ-carboline system of fac-8 enhances thermal stability compared to the pyridyl analogue fac-Ir(46dfppy)(3)10, which decomposes extensively upon being heated in glycerol at 290 °C for 2 h. Complexes mer-8, fac-8, and fac-9 are emitters of blue-green light (λ(max)(em) = 477, 476, and 494 nm, respectively). The triplet lifetimes for fac-8 and fac-9 are ~4.5 μs at room temperature; solution Φ(PL) values are 0.31 and 0.22, respectively.

New functionalized phenylpyridine ligands and their derived heteroleptic cyclometalated Ir(III) complexes have been synthesized. The complexes possess a combination of important properties: (i) blue emission, (ii) good photoluminescence quantum yields, and (iii) good solubility in organic solvents, making them very attractive as phosphorescent dopant emitters for solution-processable light-emitting devices.

One of the challenging goals of molecular electronics is to wire exactly one molecule between two electrodes. This is generally nontrivial under ambient conditions. We describe a new and straightforward protocol for unambiguously isolating a single organic molecule on a metal surface and wiring it inside a nanojunction under ambient conditions. Our strategy employs C(60) terminal groups which act as molecular beacons allowing molecules to be visualized and individually targeted on a gold surface using an scanning tunneling microscope. After isolating one molecule, we then use the C(60) groups as alligator clips to wire it between the tip and surface. Once wired, we can monitor how the conductance of a purely one molecule junction evolves with time, stretch the molecule in the junction, observing characteristic current plateaus upon elongation, and also perform direct I-V spectroscopy. By characterizing and controlling the junction, we can draw stronger conclusions about the observed variation in molecular conductance than was previously possible.

A family of new 2,5-diphenyl-1,3,4-oxadiazole (OXD) derivatives 8-11 bearing ortho-alkyl substituents on one of the phenyl rings is reported. The reactions of these OXDs with IrCl(3) under standard cyclometalating conditions did not give the usual μ-dichloro bridged diiridium OXD complexes. Instead, the novel diiridium complexes 12-14 and the monoiridium complex 15 were isolated and characterized by X-ray crystallography. It is proposed that the unusual structures arise because of the ortho-alkyl substituents leading to a substantial twisting of part of the OXD system which, for steric reasons, changes the normal course of the metal-ligand coordination reactions. Subsequent reactions of 13 and 15 gave the mononuclear complexes 16-18 with acac and picolinate anciliary ligands. The crystal structures of 16 and 18 are reported. Photoluminescence is observed in the green (16) and blue-green regions (17 and 18) at room temperature. Complexes 16-18 are phosphorescent at low temperature, with triplet lifetimes of 4.2-5.7 μs at 77 K.

The efficient synthesis and photophysical properties of a series of ambipolar donor-acceptor-donor systems is described where the acceptor is dibenzothiophene S,S-dioxide and the donor is fluorene, carbazole, or arylamine. The systems exhibit intramolecular charge transfer (ICT) states (of variable ICT character strengths) leading to fluorescence emission ranging from deep blue to green with moderate to high photoluminescence quantum yields. The emission properties can be effectively tuned by systematically changing the position of substitution on both donor and acceptor units (which affects the extent of conjugation) and the redox potentials of the donor units. The results are supported by cyclic voltammetric data and TD-DFT calculations.

The realization of molecular-scale electronic devices will require the development of novel strategies for controlling electrical properties of metal/molecule/metal junctions, down to the single molecule level. Here, we show that it is possible to exert chemical control over the formation of metal/molecule...molecule/metal junctions in which the molecules interact by pi-stacking. The tip of an STM is used to form one contact, and the substrate the other; the molecules are conjugated oligophenyleneethynylenes (OPEs). Supramolecular pi-pi interactions allow current to flow through the junction, but not if bulky tert-butyl substituents on the phenyl rings prevent such interactions. For the first time, we find evidence that pi-stacked junctions can form even for OPEs with two thiol contacts. Furthermore, we find evidence for metal|molecule|metal junctions involving oligophenyleneethynylene monothiols, in which the second contact must be formed by the interaction of the pi-electrons of the terminal phenyl ring with the metal surface.

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.

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.

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.

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.

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 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].

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.

[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 scope of the present work is to highlight the effects stemming from different C60/exTTF linkages (exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene)-either via an anthracene unit or a dithiole ring. Particular emphasis is placed on photoinduced electron-transfer features. Therefore, we devised a new series of C60-exTTF ensembles, synthesized via 1,3-dipolar cycloaddition and Diels-Alder cycloaddition reactions, in which exTTF units are separated from C60 by two single bonds (3a-c, 4), one vinylene unit (5a), or two vinylene units (5b). The cyclic voltammetry reveals an amphoteric redox behavior with remarkably strong electron-donor ability of the trimethyl-substituted exTTF moiety in 4 and 5a,b. Steady-state and time-resolved photolytic techniques show that the fullerene singlet excited state in (3a-c, 4, and 5a,b) is subject to a rapid electron-transfer quenching. The resulting charge-separated states, that is C60*(-)-exTTF*+, were identified by transient absorption spectroscopy. We determined radical pair lifetimes of the order of 200 ns in benzonitrile. This suggests (i) that the positive charge of the exTTF*+ is delocalized over the entire donor rather than localized on one of the 1,3-dithiole rings and (ii) that linking exTTF via the anthracene or 1,3-dithiole ring has no appreciable influence. Increasing the donor-acceptor separation via implementing one or two vinylene units as spacers led to improved radical pair lifetimes (5a: tau = 725 ns; 5b: tau = 1465 ns).

We report the effects of protonation on the structural and spectroscopic properties of 1,4-dimethoxy-2,5-bis(2-pyridyl)benzene (9) and the related AB coploymer poly{2,5-pyridylene-co-1,4-[2,5-bis(2-ethylhexyloxy)]phenylene} (7). X-ray crystallographic analysis of 9, 1,4-dimethoxy-2,5-bis(2-pyridyl)benzene bis(formic acid) complex 10, and 1,4-dimethoxy-2,5-bis(2-pyridinium)benzene bis(tetrafluoroborate salt) (11) establishes that reaction of formic acid with 9 does not form an ionic pyridinium salt in the solid state, rather, the product 10 is a molecular complex with strong hydrogen bonds between each nitrogen atom and the hydroxyl hydrogen in formic acid. In contrast, reaction of 9 with tetrafluoroboric acid leads to the dication salt 11 with significant intramolecular hydrogen bonding (N−H···O−Me) causing planarization of the molecule. The pyridinium and benzene rings in 11 form a dihedral angle of only 3.9° (cf. pyridine−benzene dihedral angles of 35.4° and 31.4° in 9, and 43.8° in 10). Accordingly, th...

A new ambipolar molecule based on a carbazole−fluorene−oxadiazole triad is reported. In a single-active-layer device, the compound reveals a deep-blue electroluminescence with CIE coordinates of (0, 157, 0.079). An external quantum efficiency of 4.7% is achieved if the ambipolar material is formed into a thin layer by thermal evaporation.

We report the use of the electron-donating 4,5-dipentyl-4‘-methyl-TTF (TTF = tetrathiafulvalene) moiety in combination with the electron acceptor 11,11,12,12-tetracyanoanthraquinodimethane (TCNAQ) unit in the novel D−σ−A diad molecules 11, 17, and 18. These compounds display a weak, broad, low-energy intramolecular charge-transfer (ICT) band in the UV−vis spectra (λmax 430−450 nm). Cyclic voltammetric studies show two reversible one-electron oxidation processes for the R3TTF moiety, and a reversible two-electron reduction process for the TCNAQ moiety. The electron affinity of TCNAQ is significantly enhanced by the electron-withdrawing sulfonamide and sulfonic ester groups (compounds 17 and 18, respectively). Simultaneous electrochemistry and EPR (SEEPR) experiments show no significant intramolecular interaction between the R3TTF and TCNAQ moieties in compounds 11 and 18. X-ray crystallographic data are presented for 5, 11, and 20. The structure of 5 reveals hydrogen-bonded dimers. In molecule 11 the bond ...

In this paper, we focus on the synthesis and structure of the new bis(1,3,4-oxadiazole) system 2,5-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyridine (PDPyDP). We have fabricated light-emitting diodes (LEDs) using poly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH−PPV) as the emissive material, with and without a thermally evaporated electron-injection/hole-blocking layer of either PDPyDP or its vinylene analogue (E)-1,2-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]ethene (PDVDP) or its phenylene analogue 1,4-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]benzene (PDPDP). PDPDP is the para isomer of OXD-7, which is a widely used molecular electron-transporting material. Electroluminescence spectra indicate that light is emitted only from the MEH−PPV layer. Using aluminum as the cathode, the bilayer LED with PDPyDP is considerably more efficient than the corresponding single-layer device or devices with PDVDP or PDPDP as the electron-injection layer.

We report the synthesis of a new series of cyclophanes 11a−d by ester-forming macrocyclization reactions of diol 9 with the dicarbonyl chloride derivatives of benzene, thiophene, ferrocene, and dip...

2,4,5,7-Tetranitro-9-fluorenone (1b) reacts readily with n-butanethiol in dipolar aprotic solvents with selective substitution of nitro groups by butylsulfanyl groups in positions 2 and 7 (2, 3); the 2,5-isomer 4 was formed only as a minor product (1%). Condensation of fluorenones 2-4 with malononitrile yielded 9-dicyanomethylene derivatives 5-7, which showed strong intramolecular charge transfer (lambda approximately 510-560 nm) and were found to sensitize the photoconductivity of carbazole-containing polymer films. Oxidation of sulfides 2-4 gave sulfoxide 8 or sulfones 9-11, which then were converted into their corresponding dicyanomethylene derivatives 12-15. All these novel acceptors showed three reversible single-electron reduction waves (cyclic voltammetry) yielding radical anion, dianion, and radical trianion; moreover, acceptors 13-15 showed also a fourth reduction wave, representing reversible tetraanion formation. Substitution of the oxygen of the carbonyl group in the fluorenones by a dicyanomethylene group increased the thermodynamic stability (K(SEM) growth) of the radical anion; K(SEM) ranged from 3 x 10(5) to 3 x 10(9) M(-1). CV measurements characterize compounds 3, 4 (EA = 1. 86-1.89 eV) as poor acceptors, 2, 6-11 (EA = 2.13-2.31 eV) as moderate acceptors, and 5, 12-15 (EA = 2.53-2.66 eV) as strong electron acceptors. Charge-transfer complex (CTC) formation between acceptors 9, 10, 13, 14, and anthracene as a donor was monitored by the appearance of additional low-energy bands in the visible region (CTC bands) of their electron absorption spectra. Increasing the EA of the acceptors from 9-fluorenones to the corresponding 9-dicyanomethylenefluorenes increases the complexation constants K(CTC) by 2.5-3 times, while sulfonyl substituents present substantial steric hindrance for complexation (as compared to the nitro group), decreasing K(CTC) values. Two CTCs for acceptors 14 and 17 with tetrathiafulvalene (TTF) were obtained, and their structures were solved by single-crystal X-ray diffractometry, giving the stoichometries 14:TTF, 2:3, and 17:TTF:PhCl, 1:1:0.5. In the former complex the packing motif is a mixed.DDAD'A. stack; in the latter complex the D and A moieties form unusually close CT pairs, which pack in a herringbone motif.

The synthesis and physical properties of four series of novel fluorene push−pull compounds (4−7) of the D−π−A type with intramolecular charge transfer (from 1,3- and 1,2-dithiole and 1,3-selenathiole donor (D) moieties) are described. The nature of the heteroatom (S or Se) in the donor fragment has no effect on the maxima of intramolecular absorption bands (λICT), whereas a change of position of the heteroatoms in the dithiole moiety from 1,3 to 1,2 leads to a substantial bathochromic shift in λICT. Solvatochromism, thermochromism, and negative halochromism in these compounds are demonstrated. Cyclic voltammograms of 4−7 exhibit two, separate, single-electron reversible redox waves, the potentials of which (as well as the ICT energies in the molecules) are quantitatively described by σp- constants of the substituents in the fluorene ring. Compounds 4−7 exhibit reversible salt formation in sulfuric acid, and for compound 5g in diluted sulfuric acid an additional absorption in the near-IR region has been ob...

The synthesis and physical properties of a series of novel fluorene π-electron acceptors (7−9) are described. Cyclic voltammograms of 7 and 8 exhibit three separate reversible (or quasi-reversible) one-electron redox waves, characteristic of strong electron acceptors. Spectroelectrochemical experiments show the appearance in the long-wavelength visible region of absorption bands at appropriate potentials which were attributed to the transformations A → A•- and A•- → A2-. Charge-transfer complexation with N-propylcarbazole in dioxane shows the formation of 1:1 complexes with parameters characteristic for other fluorene acceptors. The single-crystal X-ray structures of 1:1 charge-transfer complexes of tetrathiafulvalene with the electron acceptor 8 and with the strongest fluorene acceptor 1f both show ··A···D···A···D·· stacking in the crystal.

The properties of new 2,2‘-ethanediylidene(1,3-dithiole) derivatives 5, 6, and 8−11 are reported. Cyclic voltammetric studies establish that they are efficient donor molecules, with the extended conjugation resulting in stabilization of dications, relative to tetrathiafulvalene TTF (1). Radical cations are generated by oxidation of the neutral compounds with trifluoroacetic acid or anhydrous silver perchlorate in dichloromethane, and their ESR and proton ENDOR spectra are reported. The bulk of the spin population resides in the central S2CCCCS2 part of the π-system. The X-ray crystal structure of donor 6 reveals that the 2,2‘-ethanediylidene(1,3-dithiole) framework is planar. Donor 6 forms a crystalline 1:1 charge-transfer complex with TCNQ, the X-ray crystal structure of which shows a mixed stack structure. A solution of this complex in acetonitrile exhibits ESR spectra of both radical ions, 6·+ and TCNQ·−. Static susceptibility data are reported for TCNQ complexes of some of these donors.

The formation of high-quality Langmuir−Blodgett films of copper and nickel phthalocyanine derivatives substituted with short branched chains is reported. Ellipsometric and polarized optical absorption measurements suggest that the phthalocyanine molecules have a preferred orientation, with their large faces perpendicular to the dipping direction and to the substrate plane. Electrochromic effects are also noted in these multilayer films.

The title Wittig reagent (5) has been prepared in three steps (84% overall yield) from 4,5-bis-(benzoylthio)-1,3-dithiole-2-thione. Reac- tions of ylide (7), generated by treatment of (5) with diisopropyle- thylamine at room temperature, have been exploited in the synthesis of new unsymmetrical tetrathiafulvalenes and 1,3-dithiol-2-ylidene deriva- tives. Subsequent removal of the benzoyl protecting group with sodium ethoxide liberates the transient TTF-dithiolate or 1,3-dithiole-dithi- olate anions which can be alkylated in situ. The X-ray crystal structu- res of compounds (17) and (18) are reported: close nonbonded S-O intra- molecular interactions are observed in both structures

A range of new bis- and tris-TTF derivatives has been prepared using the TTF-thiolate anion 2 as a key intermediate. Thiolate anion 2 reacts with 2-bromoethanol to yield alcohol 3 from which the bis- and tris-TTF systems 4-7 have been obtained by reaction with the appropriate acid chloride. Subsequent reactions of the malonate anion of dimeric TTF 7 yield derivatives 8-10, which include the amphiphilic system 8

Efficient syntheses are described for five new vinylogous π-electron donors, viz. 5, 6, and 8-10, which are related to bi(ethylenediseleno)tetrathiafulvalene (3): symmetrical and unsymmetrical systems, containing mixed alkylseleno and alkylthio groups, have been obtained. The solution electrochemical redox properties, studied by cyclic voltammetry, establish that these molecules undergo two, single-electron, oxidations at low potentials. The single-crystal X-ray structure of 4,5-bis(methylseleno)-4',5'-bis(methylthio)-2',2'-ethanediylidene(1,3-dithiole) (6) is reported

The reaction of a range of quinones 3 with malononitrile in the presence of titanium tetrachloride/pyridine yields dicyanoquinomethides 4, which on reaction with N,N'-bis(trimethylsilyl)carbodiimide are converted into the corresponding N,7,7-tricyanoquinomethanimines 6. The solution electrochemical redox properties of compounds 6 have been studied by cyclic voltammetry; they are strong acceptors which readily form radical anions and dianions

La synthese stereoselective d'amino-2' aryl-10- et formylmethyl-2' aryl-10 aza-1 spiro [4.5] decene-7ones-2 est presentee ainsi que la cyclisation de ces spiranes en derives de benzodioxolo [5,6-d] pyrrolo [2,1-k] benzodiazepine-1,3, de dibenzo [b,d] pyrrolo [1,2-a] azepine et de benzodioxolo [5,6-d] pyrrolo [2,1-k] benzoazepine-1

The complexation of TTF 2 and cyclobis(paraquat-p-phenylene) 14+ has been studied by cyclic voltammetry and by spectroelectrochemistry: shifts in the redox potentials for the TTF and the 14+ components of 45 and 30 mV, respectively, occur upon complexation. Decomplexation of 2·14+ upon oxidation of the TTF unit to the cation radical species has been monitored by spectroelectrochemistry. The complexation/decomplexation process is highly reversible over at least 10 electrochemical cycles, and this process is accompanied by a color change of the solution from dark green (complexed) to pale brown (uncomplexed) which is clearly visible to the naked eye.

Fourier transform infrared spectroscopy has been used to study molecular ordering and conductivity processes of a HDTTF charge-transfer salt deposited in Langmuir-Blodgett multilayers onto silicon and metal substrates. Both the chemistry and the degree of conductivity may be easily monitored «in situ» as a function of doping level. Linear dichroism measurements confirm the vertical alignment of hydrocarbon chains needed to produce lateral electron mobility via well-ordered, fulvalene rings

A simple two-probe apparatus used to measure the room-temperature d.c. conductivity of solids in the form of compressed pellets.