Vladimir Khodorkovsky

Do π-dimers of tetrathiafulvalene cation radicals really exist at room temperature?

The longest wave absorption band of the tetramethylthio- tetrathiafulvalene cation radical, which is usually interpreted as a π-dimer band, is shown to be the intrinsic cation radical absorption, all studied cation radicals in solution at room temperature exist as paramagnetic monomers and only tetrathiafulvelene and tetramethyltetrathiafulvalene cation radicals undergo π-dimerization at low temperatures.

Tetrathiafulvalene: gas-phase molecular structure from electron diffraction

Abstract The gas-phase molecular structure of 2,2-bi-1,3-dithiole (tetrathiafulvalene) was determined by electron diffraction and compared with the crystal molecular structure. A nonplanar “boat” structure was found to give the best agreement with experimental electron diffraction results. The electron diffraction results were found to be consistent overall with those from X-ray crystallographic studies.

Synthesis of 2,3-dimethylthio-6-pyridyl tetrathiafulvalene: a precursor for a new system involving a direct linkage between a strong donor (D) and a strong acceptor (A)

Abstract A multi-step synthesis of a novel tetrathiafulvalene derivative involving a 4-pyridyl substituent directly attached to the TTF moiety is described.

Synthesis and intramolecular charge-transfer properties of new tetrathiafulvalene–σ-tetracyanoanthraquinodimethane diad (TTF–σ-TCNAQ) and triad (TTF–σ-TCNAQ–σ-TTF) molecules

We report the use of functionalised electron acceptor tetracyanoanthraquinodimethane (TCNAQ) units in the synthesis of novel diad D–σ-A compounds 6 and 7 [D=tetrathiafulvalenyl (TTF) and ferrocenyl] and the triad TTF–σ-TCNAQ–σ-TTF assembly 8. Compounds 6–8 display a very weak, broad, low-energy intramolecular charge-transfer band in the UV–VIS spectra. Nanosecond laser flash photolysis of compound 6 did not lead to any new transient absorptions in the 300–800 nm region, suggesting that if a charge-separated species is formed upon excitation, then back electron transfer occurs very rapidly to regenerate the ground state. Cyclic voltammetry of compounds 6–8 shows that reversible oxidation processes occur for the TTF and ferrocene moieties, and a reversible two-electron reduction occurs for the TCNAQ moiety. Spectroelectrochemical studies on compound 6 have enabled the redox processes to be assigned to the sequential formation of the TTF radical cation and dication upon oxidation, and the TCNAQ dianion upon reduction. Simultaneous electrochemistry and EPR (SEEPR) experiments provide further evidence for intramolecular interaction between the TTF and TCNAQ moieties in compound 6. Quantum mechanical calculations on compound 6, performed by the AM1 method, predict that in its minimum energy conformation the TTF and TCNAQ moieties are approximately orthogonal to one another, with the TCNAQ unit folded into a butterfly conformation.

Semiconducting Langmuir–Blodgett films of ethylenedithiotetrathiafulvalene (EDT–TTF) derivatives bearing charged and uncharged aromatic substituents

Ethylenedithiotetrathiafulvalene (EDT–TTF) derivatives1–4 functionalised with a single aromatic ring have been synthesised and their Langmuir–Blodgett (LB) films have been assembled utilising only 25% molar ratio of fatty acid. For compounds 1, 3 and 4, predominantly Y-type deposition onto solid supports was observed with a transfer ratio close to unity. After doping with iodine vapour, the maximum in-plane conductivity values obtained were σ rt =10 -3 S cm -1 for 1 and 3, and 10 -5 S cm -1 for 4. LB deposition of 2 was not uniform and the conductivity value after doping was low. UV–VIS spectra of the LB films reveal the appearance of a charge-transfer (CT) band at λ max =ca. 900 nm for 1 and 4 after iodine doping. A solution of compound 3 exhibited a weak absorption band at ca. 665 nm which is assigned to an intramolecular CT band; the intensity of this band increases on exposure of the solution to light. This band is not observed in LB films of 3, neither as-deposited nor after doping. Molecular orbital calculations indicate that in the minimum energy conformation of 3, the pyridinium moiety is practically orthogonal to the TTF unit and this conformation may be obtained in solution, enabling charge-transfer to occur. A more linear conformation of 3 in the LB films may prevent intramolecular charge-transfer from occurring. Monolayers of 1, 3 and 4 were characterised by cyclic voltammetry which revealed two redox steps consistent with the formation of the EDT–TTF cation radical and dication, respectively.

Novel fluorescent stilbene analogs involving a carbazole moiety

Abstract The synthesis of a series of novel efficient TPA chromophores involving a carbazole moiety from N -( p -formyl)phenylcarbazole precursors and their linear absorption and fluorescent properties are described.

2-D effects in the second-order optical nonlinearity of organic molecules incorporating carbazole

Abstract The second order nonlinearity ( β ) of a series of organic π-conjugated molecules involving 1,3 indandione derivatives as an acceptor moiety has been measured. The effect of varying the donor from dialkylamino to N -carbazolyl substituents was examined. Despite the chemically similar nature of the two donors, a drastic reduction of electric field induced second harmonic (EFISH) β values for the molecules involving the N -carbazolyl substituents was detected. Quantum mechanical calculations indicate that the decrease in β values results from the presence of two overlapping transitions that contribute to β with opposite signs. Thus, the charge transfer band gives a positive β zzz contribution along the long molecular axis, while a transition essentially within the carbazole group provides a negative β zxx contribution to β EFISH . Therefore, these molecules can only be described with a two-dimensional model as opposed to the ‘classical’ one-dimensional model for NLO chromophores. Experimental verification of this hypothesis was provided by a combination of two experimental methods, EFISH and hyper Rayleigh scattering (HRS). Each technique probes a different combination of the β tensor elements, so we could deduce the two contributions.

Semiconducting Langmuir–Blodgett films of non-amphiphilic ethylenedithio–tetrathiafulvalene derivatives bearing pyridine and pyridinium substituents

Compounds 1 and 2 form stable Langmuir–Blodgett films which after iodine doping are semiconducting (σrt= 10–3 S cm–1), demonstrating that the attachment of long alkyl chains is not a prerequisite for the formation of conducting LB films of tetrathiafulvalene (TTF)-based charge-transfer complexes.

New η-electron donors containing two tetrathiafulvalene units fused to 1,4-dithiine and a conducting charge-transfer complex with tetracyanoquinodimethane

The Synthesis of new electron donors containing two TTF units fused to 1,4-dithiin and a crystal structure of a conducting charge-transfer complex is described.

Tetrathiafulvalene-thioindigo annelated donor-acceptor system with intramolecular charge transfer

Abstract The synthesis, UV–vis spectra, X-ray structure and redox properties of novel models for intramolecular D–A interaction, which incorporate tetrathiafulvalene and a thioindigo basic chromophoric system, are described.