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This work presents two new amphiphilic molecules derived from the tetrathiafulvalene (TTF) cycle. The purpose of this work is to realize a controlled in-plane molecular architecture. In order to obtain well organized macrocycles at the air-water interface we have added to the TTF cycle four long alkyl chains, each with an acid (or ester) group. Compound I has been designed to form a regular paving in the polar plane whereas for compound II an identical arrangement in the hydrophobic plane is predicted. The synthesis and thermodynamic stability of the monolayers are investigated for both molecules. The results show that these macrocycles are lying flat on the water surface: this is the first step in two-dimensional molecular engineering.

Molecular assemblies were studied at the air-water interface, as were neutral and oxidized Langmuir-Blodgett (LB) films in the mixed (1: n) molecular system of EDTTTF (SC18)2 (EDTTTF, ethylenedithiodioctadecylthiotetrathiafulvalene) and behenic acid (CH3(CH2)20 COOH). At the air-water interface, a possible molecular organization was discussed from the study of the area occupied by EDTTTF (SC18)2 and n molar fraction of behenic acid at a surface pressure of 30 mN m-1. EDTTTF (SC18)2 molecules form dimers and with increasing behenic acid content, a monolayer reorganization occurs. The formation of monomolecular layers including monomer EDTTTF (SC18)2 molecules was achieved for n>or=2. X-ray diffraction studies were concentrated on samples of Y-type LB multilayered films with n=0, 1 and 3. Throughout the mixed (1:n) system, stacking periodicity was dominantly observed from (001) reflections as 55+or-1 AA for neutral films, 72+or-1 AA for a brown-coloured film after exposure to iodine, and 46+or-1 AA for the stable, conducting and purple-coloured film after a thermal activation process. Possible molecular assemblies based upon centrosymmetrical bilayers were qualitatively discussed based on the calculation of the linear electron density profiles of pure and doped EDTTTF (SC18)2 LB films. The large variation of the stacking periodicity during the oxidation process was explained by the molecular inclination of EDTTTF (SC18)2 molecule associated with the insertion of I3- ions which intercalate between EDTTTF (SC18)2 layers.

Conducting LANGMUIR-BLODGETT films (LB) present a great deal of interest for molecular electronic devices and chemical sensors. We reported that 1:1 mixture of a fatty acid with ethylenedithiodioctadecylthio-tetrathiafulvalene give LB films which become conducting after iodine exposure (1). For a better understanding of the iodine doping mechanism, we have analysed the infrared spectra evolution of films versus time. In a first step a new absorption line is observed at 1333 cm −1 and attributed to a charged dimeric form, while the films are still insulating. After a couple of hours at room temperature, the intensity of the 1333 cm −1 line decreases to zero and a new broad charge-transfer band associated to an intense absorption centered at 1250 cm −1 of vibronic origin is detected. The final state corresponds to the conducting phase already described (1). Raman spectroscopy on the latter phase indicates the formation of the I 3 - species which are ordered in chains. A mechanism of the doping process is proposed from which the film stoichiometry is derived.

Mixtures of ethylenedithio-dioctadecylthio-tetrathiafulvalene (EDT-TTF(SC 18 ) 2 ) with behenic acid form Langmuir-Blodgett films of Y-type characterized by islands of EDT-TTF(SC 18 ) 2 in a matrix of the fatty acid. A two-step oxidation (immersion in I 2 vapours followed by heating at 40°C) gives: • - an insulating brown phase with I 3 -isolated species. • - a conductive violet phase with I 3 -chains associated with a mixed valence state and a large structural reorganization.

The photodecomposition of the rhodamine 6G (R6G) dye dissolved in n -alcohols and aqueous sodium dodecylsulphate (SDS) micellar solution was investigated under continuous UV-visible illumination. The results indicate that in alcohol solution the photodecomposition efficiency increases with the dye concentration. It also depends on the nature of the alcohol the lowest efficiency being observed in ethyleneglycol. The mechanism involves the electron transfer reaction of the triplet excited state with a ground state dye molecule (T + S 0 → R + + R − . In aqueous SDS micellar solution, the R6G cation is embedded in the hydrophobic interior of the micelle close to the negatively charged sulphate end groups. We show that a rather high concentration (3 × 10 −3 M) of R6G can be dissolved in 10 −1 M SDS aqueous solution, protecting R6G from the electron transfer reaction and secondary decomposition reactions.

We study an electrochemical method of obtaining conducting Langmuir-Blodgett films as radical cation salts of dialkylthioethylenedithiotetrathiofulvalence (TTF) derivatives. We show an electro-oxidation of the TTF moiety through the films. The mixed-valence state responsible for the conductivity phenomenon is generally not obtained except with iodide electrolyte, under potentials larger than 0.45 V SCE and after a thermal treatment.

The static magnetization and magnetic susceptibility anisotropy of (TMTTF)2 X(where X = AsF6 and SbF6) have been investigated between 3 and 300 K for magnetic field strengths up to 50 kG. A spin Peierls phase transition is observed in AsF6 salt around 11 K, whereas in the (TMTTF)2 SbF6 compound an antiferromagnetic (AF) transition is detected around 7 K.

We have synthesized a new hexakis (alkylthio) benzene possessing C 3 symmetry. From this tris-(ethylenedithio) benzene (TEDTB), a radical cation fluoroborate salt of 2.1 stoichiometry, has been prepared and investigated. The room temperature crystal structure shows that this salt crystallizes in an orthorhombic system and presents segregated dimerized stacks of TEDTB. The electric properties exhibit a semiconducting behaviour around room temperature, while low-temperature characteristics need further investigation. We believe that the TEDTB molecule is indicative of a potentially exciting series of donor molecules.

We have synthesized a new series of hexakis (alkylthio) benzenes with C3 molecular symmetry. From these π donor molecules we have prepared a radical cation salt and several charge transfer complexes which have been physically characterized mainly by magnetic experiments. These results are presented and discussed within the scope of possible ferromagnetic systems.

The optical properties of the radical cation salts based on the unsymmetrical molecule dimethylethylenedithiotetrathiafulvalene (DIMET) and associated with centrosymmetrical counter ions (AsF 6 − and SbF 6 − ) have been explored and compared with other salts. Their vibrational spectra (IR and Raman spectroscopies) as well as the electronic charge transfer bands have been studied between 300 K and 10 K. As in other (2-1) radical cation salts characterized by a structural organization of centrosymmetric dimers, we have found vibronic lines at any temperature, but they behave differently for the two salts. We have also fitted the C.T. absorption bands using a Drude-Lorentz model, which allows us to show that the present energy gaps are basically of a Hubbard type. As confirmed by a comparison with the known magnetic properties, we find that the electronic correlations are the dominant interactions in these compounds with narrow electronic bands.

Electrical conductivity and ESR experiments on several new salts of the unsymmetrical molecule dimethylethylenedithiotetrathiafulvalene are described. According to the ESR results, the compounds can be classified in two groups labelled α and β. The α compounds present similar magnetic behavior with an increase of the spin susceptibility at low temperature. The properties of the β samples are reminiscent of those of the TMTTF salts exhibiting either a spin-Peierls or an antiferromagnetic ground state below 20 K.

The cations of the new series of hexakis(alkylthio)benzenes with C3 symmetry have been studied in solution as well as in solid state. Dications are more stable in acidic medium and the second redox potential appears to be higher than for hexamethoxytriphenylene (HMT). Electronic spectra of monocations show molecular excitation bands without evidence for dimer species. ESR spectra present sometimes an hyperfine structure indicating a mean C3 symmetry. Dications are chemically less stable and we have not been able to detect a triplet state. We suspect that a Jahn-Teller distorsion could cause the dication to have a singlet ground state. In solid state crystals of triethylenedithiobenzene-tetrafluoroborate (tEDT-B)2BF4 have a charge transfer band corresponding to a mixed valence state. The complexation with tetrafluorotetracyanoquinodimethane gives crystals of (tEDT-B)2TCNQF4 which present stacking columns of alternating donor dyads and acceptor monads (DAD units) with an intense charge transfer ban...

A new antiferromagnetic organic salt, (DIMET) 2 SbF 6 is presented. The peculiar, strongly dimerized structural arrangement of this salt allows its description in terms of quasi-isolated dimers. In this modelization the exchange coupling constants are deduced from transfer integrals and the anisotropy energy is calculated from dipolar interactions. The good agreement found between our description and experimental results is an asset for discussion about the origin of antiferromagnetism in organic conductors.

The low-temperature phase transitions of tetramethyltetrathiafulvalene thiocyanate are described through magnetic and structural studies. A first transition, which occurs at 160 K, drives the electron gas into a localized state and is shown to be associated with a superstructure formation. Then, the condensation of an unexpected antiferromagnetic ground state is observed around 7 K. We suggest that this striking behavior is related to the peculiar wave vector (${a}^{*}, \frac{1}{2}{b}^{*}, \frac{1}{2}{c}^{*}$) of the 160-K superstructure.

Langmuir-Blodgett films of a long chain tetrathiafulvalene (TTF) donor derivative (BEDT-TTFC 18 ) were deposited onto different substrates for investigating several physical properties before and after doping by a few oxidizing agents. In the presence of ICl vapour, two different phases, insulating and semi-conducting, were obtained, as shown by electron spin resonance, IR and Raman spectroscopies. From these preliminary results, it seems that the doping chemical process is different from the well known charge transfer occurring in organic conductors.

The low-temperature magnetic properties of (DIMET)2SbF6 have been probed by antiferromagnetic resonance experiments and the parameters which characterize the magnetic ordering are determined. Taking advantage of the structure of this compound which presents strongly dimerized dimers, we show that our results can be quantitatively explained using standard expressions for both the exchange and the anisotropy energies. Finally a brief comparison with other antiferromagnetic organic materials is presented.

Experimental results concerning laser action as a function of temperature of trans-1,1,4,4 tetraphenyl-butadiene in cumene are reported. At room temperature laser action is observed at 4980 A, whereas between -70°C and -80°C laser action occurs simultaneously at 4980 A and 4350 A, and below -80°C only emission at 4350 A is observed. The normal fluorescence of trans-1,1,4,4 tetraphenyl-butadiene exhibits a maximum at 4550 A, byt a new emission band with a maximum near 5040 A appears for high excitation energies below the lasing treshold. The intensity of this new band increases non-linearly with the excitation intensity. At low temperatures and high excitation energies this band disappears. It is concluded that at room temperature the laser effect in this compound arises from a photochemical species formed from the first excited singlet state of trans-1,1,4,4 tetraphenyl-butadiene. It is suggested that this species is a photoisomer and different hypotheses are discussed.

The anisotropy in the static magnetic susceptibility of some tetramethyltetrathiafulvalene salts (TMTTF)2X (where X- = PF-6, ClO-4, SCN- and Br-) has been investigated with a torque method between 3 K and 300 K for magnetic fields up to 11 kG. The experimental results show that the salts with X- = SCN- and Br- become antiferromagnetic at about 8 and 13 K respectively, whereas for the two other salts above 1 kG no field dependence of the magnetic susceptibility is observed down to 3 K.

Laser action has been observed in nine phenyl-oxadiazole derivatives between 3585 A and 3465 A. The new dye lasers were pumped by means of a KrF electric discharge laser.