Ajaib S. Dhindsa

Bis(tetrathiofulvalenyl)sulphide [(TTF)2S] : synthesis and x-ray crystal structure

Abstract Bis(tetrathiafulvalenyl)sulphide [(TTF)2S] has been synthesized by reaction of monolithiated TTF with di(phenylsulphonyl)sulphide, and characterised by cyclic voltammetry and single crystal X-ray analysis, which reveals a remarkably close two-dimensional chalcogen network in the solid state. The synthesis of (TTF)2Se, using the selenating reagent di(phenylsulphonyl)diselenide, is also reported. Bis(tetrathiafulvalenyl)sulphide [(TTF)2S] has been synthesised by reaction of monolithiated TTF with di(phenylsulphonyl)sulphide, and characterised by cyclic voltammetry and single crystal X-ray analysis, which reveals a remarkably close two-dimensional chalcogen network in the solid state. The synthesis of (TTF)2Se, using the selenating reagent di(phenylsulphonyl)diselenide, is also reported.

Electroactive langmuir-blodgett films of N-octadecylpyridinium-TCNQ charge-transfer salt

Abstract Langmuir-Blodgett films of the 1 : 1 charge-transfer salt N -octadecylpyridinium-TCNQ have been deposited onto glass substrates. The layers exhibit significant bulk lateral conductivity without doping . The value obtained at room temperature is (2.0 ± 0.2) × 10 −2 S cm −1 ; over the temperature range 100 – 300 K, the films show typical semiconductor behaviour with an activation energy of 0.13 ± 0.005 eV. Infrared and u.v.-visible transmission spectra of the films are characteristic of an organic conductor.

Structural properties of Langmuir-Blodgett films of a long-chain tetrathiafulvalene derivative

Abstract An investigation into the molecular arrangements in Langmuir-Blodgett films of hexadecanoyltetrathiafulvalene is reported. Low-angle X-ray diffraction shows that, as deposited, the layers are organised in a simple head-to-head and tail-to-tail configuration (i.e. Y-type deposition). However, on doping with either iodine or bromine, the X-ray d-spacing is significantly reduced, implying that the molecules become interdigitated, tilted or both. The formation of a charge-transfer band for the iodine-doped multilayers is confirmed by IR spectroscopy. Experiments using X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy reveal that the semiconducting properties of these samples are probably the result of the formation of a mixed-valence charge-transfer complex.

Alternate-layer Langmuir-Blodgett films of long-chain TCNQ and TTF derivatives

Abstract Langmuir-Blodgett films of a long-chain TCNQ derivative alternated with a long-chain TTF compound have been deposited onto glass substrates. These layers exhibit a bulk lateral conductivity of (5±1) × 10 −3 S cm −1 at room temperature. Over the temperature range 100 – 300 K, typical semiconducting behaviour is observed, with a thermal activation energy of 0.26 ± 0.01 eV.

Unsymmetrical and highly-conjugated tetrathiafulvalene and selenatrithiafulvalene derivatives: synthesis and reactions of novel heterocyclic Wittig–Horner reagents

Novel 1,3-dithiole and 1-selena-3-thiole Wittig–Homer reagents have been developed and used in the efficient synthesis of a range of new, unsymmetrical tetrathiafulvalene and selenatrithiafulvalene derivatives (6)–(10) and (16); cyclic voltammetry establishes that these molecules are efficient π-donors.

Electroactive Langmuir-Blodgett films of hexadecanoyl-TTF

Abstract Hexadecanoyltetrathiafulvalene (HDTTF) has been prepared by reaction of the lithium salt of TTF with hexadecanoyl chloride. Multilayers of HDTTF have been assembled on glass substrates; upon doping with iodine the films become highly insulating, but the conductivity increases with time following exposure, to reach a maximum value of 0.01 S cm −1 after a few hours. In contrast to this, films doped with bromine remain insulating.

Preparation and characterisation of conductive Langmuir–Blodgett films of amphiphilic pyridinium–ni(dmit)2 salts

The behaviour of (N-octadecylpyridinium)–Ni(dmit)2 at the air/water interface has been investigated, and Langmuir–Blodgett (LB) films have been built up on a variety of substrates. LB layers deposited from freshly spread, floating films are composite structures, containing aggregates of micrometre dimensions. True monolayers are obtained only if the floating film is left for several hours on the subphase surface in its uncompressed state. The spectroscopic and electrical properties of both types of LB film are reported. For the composite layers, stable, in-plane do conductivity values of up to 0.2 S cm–1 are obtained after doping in iodine vapour. However, LB films built up from floating monolayers are not conductive, either in their as-deposited state or following iodine doping.

Electrical properties of Langmuir-Blodgett films of a Ni(dmit)2 charge-transfer complex

Abstract Multilayer structures of a (N-octadecylpyridinium)2-Ni(dmit)2 charge-transfer complex (H2dmit = 4,5-dimercapto-1,3-dithiole-2-thione) have been deposited onto glass substrates by the Langmuir-Blodgett technique. Electrical measurements have been made over the temperature range 100–300 K in the as-deposited state and after chemical doping with iodine. Room temperature in-plane conductivities were 6 × 10−6 S cm−1 and 0.2−0.8 S cm−1 for films as-deposited and after iodine doping, respectively. As-doposited, a linear current versus voltage characteristic was observed and a plot of log (current) versus reciprocal temperature was found to consist of more than one straight line section. Activation energies of 0.59 eV, 0.32 eV and 0.14 eV were measured over different parts of the temperature range studied. After doping with iodine, a current versus voltage plot with a “super-Ohmic” section was noted. In this case, two different activation energies were found; 0.17 ± 0.2 eV at low bias and 0.09 eV for higher applied voltages. A study of the stability of conductivity with time has also been undertaken; films were found to be stable for a period of at least 1 month.

Electroactive Langmuir-Blodgett films of O-hexadecylthiocarboxytetrathiafulvalene (HDTTTF)

The title compound forms stable, high-quality Langmuir-Blodgett films which are highly conducting after iodine doping (σmax.1.0 ± 0.2 S cm–1); the films have been characterised, in the as-deposited and doped states, by variable temperature conductivity experiments, UVNIS, IR, and photoelectron spectroscopy, and by low-angle X-ray diffraction.

Conducting Langmuir-Blodgett films of 1-tetrathiafulvalenyl-octadecan-1-ol-TCNQ complex

The title compound was prepared by reducing octadecanoyl-TTF with lithium aluminium hydride and subsequent complexation with TCNQ. Langmuir-Blodgett films of the complex could be built-up on glass or calcium fluoride substrates. These multilayer films have been characterised by UV-visible and infrared spectral measurements. Conductivity values at room temperature of around 10-3 S cm-1 were obtained, with an activation energy of 0.27 eV over the temperature range 80-320 K.