Synthesis and electrical conductivities of charge-transfer complexes of bis(vinylenedithio)tetrathiafulvalene and its methyl derivatives with strong acceptors

Charge-transfer complexes of bis(vinylenedithio)tetrathiafulvalene (VT), bis(methylvinylenedithio)tetrathiafulvalene (DMVT) or bis(dimethylvinylenedithio)t tetrathiafulvalene (TMVT) with several strong acceptors, such as TCNQ, F₄TCNQ, DDQ, TCNE, Bu₄NBr₃ and I₂, were synthesized by leaving the mixed solution of a donor and an acceptor to stand at ambient temperature. Not only the usual 1:1 (donor:acceptor) complexes but also 2:1, 1:2, 3:1, 3:2 and 5:2 ones were obtained. Unfortunately, a single crystal of good quality was not obtained. The electrical conductivities of the compressed pellet samples were measured by van der Pauw's method. Most of them showed high conductivities of 10⁰–10⁻¹ S cm⁻¹ at room temperature. However, the TCNQ complexes were insulators. The electrical conductivities could be explained on the basis of the i.r. spectra of the complexes and the redox potentials of the donor and acceptor molecules.     

Synthesis and conductivities of (μ-cyano)phthalocyaninatometal compounds

A review of the synthesis and characterization of a new type of stacked, bridged macrocyclic metal complexes, the (μ-cyano)phthalocyaninatometal compounds [PcMCN]_n (2) is given. By using the routes described in Fig. 3 the polymers were synthesized with M = Co³⁺, Fe²⁺, Fe³⁺, Mn³⁺ and Cr³⁺ as the central metal ion. The compounds were characterized by IR, far-IR, UV, thermal and elemental analysis, and partly by ¹H NMR and FD (field desorption) mass spectroscopy.[PcCoCN] (2a) and [PcFeCN]_n (2b) exhibit d.c. room temperature conductivities around 10^?2 S/cm without doping, thereby showing conductivities which are in the same range as the iodine-doped phthalocyaninatosiloxanes [PcSiO]_n.     

Comparative studies on electrical and optical properties of iodine-doped (CH)x and (CD)x

The isotope effect of deuterium on the electrical conductivities of iodine-doped PA is studied over a wide temperature range. The reflection spectra of (CDI_y)_x are also compared with those of (CHI_y)_x. The electrical conductivities are analysed by one- and two-dimensional hopping models. The importance of the electron-phonon coupling, the phonons being the charged soliton vibrational modes, is stressed. A characteristic of polaron hopping is found in the dimensionality crossover of the electrical conduction at low temperature. The electronic structure of the iodine-doped PA is discussed from electrical and optical aspects.     

Investigation of photoinduced change of dielectric and electrical properties of indium (III) phthalocyanine and fullerene doped nematic liquid crystal

In this work, we have studied photoinduced dielectric and electrical properties of E63 nematic liquid crystal (E63-LC) materials doped with indium (III) metallo phthalocyanine (In-MPc) and fullerene (C₆₀) in dark and under UV illumination. Doping concentration of In-MPc in E63-LC was chosen to be 5 wt%, whereas a trace amount of C₆₀ was used in investigated samples. Real and imaginary parts of dielectric permittivity were investigated in the frequency range of 100 Hz–10 MHz by using dielectric spectroscopy technique (DST). It was observed that doping agents and UV illumination enhanced the real part of dielectric permittivity at low frequencies, which was thought to originate from photoinduced charge transfer between In-MPc and C₆₀ caused by extra dipole strength in LC medium. In addition to that, critical frequency (f_c) and relaxation time (τ) were obtained and analyzed for all investigated samples. Photoelectrical characteristics of hybrid LC structures were carried out by current–voltage measurements. A major increase in electrical conductivity was observed in In-MPc and C₆₀ doped LC structures under UV irradiation.     

Electrical conductivity of organosilicon polymers II: Synthesis and electrical conductivities of iodine-doped polysilanes containing amino groups

A series of polysilanes containing an N,N-dimethylaminophenyl group and N-pyrrolyalkyl group as in the side chain were prepared by the Wurtz coupling polymerization. The polymerization of N-pyrrolylbutyl or N-pyrrolylhexyl-substituted dichlorosilane with sodium gave successfully the polysilanes with higher molecular weight than 10⁵. The electrical conductivities of I₂-doped polysilanes were dependent on the chemical structure of the amino side chain. Moreover, by use of excess iodine, the conductivity of the polymer was enhanced. The electrical conductivity of poly[bis(6-(N-pyrrolyl)hexyl]silane] (7a) increased to a maximum value of 8 × 10⁻² S/cm.     

Field,temperature and thickness dependent electron transport in 5,5′-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole)

Charge transport in 5,5′-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is investigated as a function of temperature and organic layer thickness. The thickness dependence of the current indicates towards the trap charge limited conduction (TCLC) with a field and temperature dependent mobility. The density of trap states has been found to be dependent on sample thickness. As the thickness has increased from 80 nm to 120 nm, trap energy has correspondingly increased from 78 meV to 130 meV. TCLC model with Poole Frenkel type field dependent mobility has been fitted into the data and has been found in excellent agreement. Temperature dependency of zero field mobility (μ₀) and β has been estimated from the model.     

Formation and characterization of copper tetrakis (4-cumylphenoxy) phthalocyanine:perylene solar cells

Perylene-based bulk heterojunction solar cells with copper tetrakis (4-cumylphenoxy) phthalocyanine (Tc-CuPc) and heterojunction solar cells with copper phthalocyanine (CuPc) were produced and characterized. A device based on CuPc and perylene provided better efficiency, fill factor, short-circuit current and open-circuit voltage compared to those of a device based on Tc-CuPc and perylene. The Tc-CuPc:perylene structure was examined by transmission electron microscopy, which indicated mixtured microstructure. Energy levels of the molecules were calculated and discussed.     

AC conductivity and dielectric measurements of bulk magnesium phthalocyanine (MgPc)

The AC conductivity, σ_ac(ω) for bulk magnesium phthalocyanine (MgPc) in the form of compressed pellet in the frequency range of 1–500 kHz and in a temperature range of 303–443 K with evaporated ohmic Au electrodes have been investigated. The frequency dependence of the impedance spectra plotted in the complex plane shows semicircles. The Cole–Cole diagrams have been used to determine the DC conductivity. The AC conductivity, σ_ac(ω), is found to vary as ω^s in the frequency range of 1–500 kHz. At high range of frequency, s < 1 and it decreases with increasing the temperature. The variation of s with temperature suggests that the AC conduction is due to the correlated barrier hopping (CBH). The dielectric constant, ′, and dielectric loss, ″, for bulk MgPc were decreased with increasing frequency and increased with increasing temperature.     

Metal complexes of (LH2) ligand: 8,9-bis(hydroxyimino)-4,7,10,13-tetraaza-1,2,15,16-O-dicyclopentylidenehexadecane: Crystal structure,electrical and optical properties

Molecular semiconducting complexes constitute one of the most fascinating, recent research topics, deeply involving both chemists and solid states physicists. Considerable interest has been shown in the synthesis and study of molecular complexes which may behave like semiconducting materials or at least show high conductivities. In this study, structural, electrical and thermal conductivity and optical properties of some inorganic complexes were investigated. From the XRD data, the unit cells of the samples were found as L–Cu is amorphous and L–Ni, L–Co are orthorhombic. L–Cu, L–Ni and L–Co have n-type of electrical conductivity. Electrical and optical band gaps of the complexes were found to be 1.46–1.36, 2.68–2.71 and 1.40–1.32 eV, respectively.     

Multiple reduction states with different conductivities of polybenzimidazobenzophenanthroline (BBL) studied with infrared spectroelectrochemistry

Polybenzimidazobenzophenanthroline (BBL), a conjugated ladder polymer, has interesting features such as n-type conductivity, good photoconductivity, large nonlinear optical properties and the highest electron affinity among known n-type semiconducting polymers, which makes the material an interesting candidate for optoelectronical applications. BBL can be reduced (n-doped) electrochemically and shows various reduction states. We report results on FTIR spectroelectrochemical studies of the reduction reactions using ATR-FTIR spectroscopy. The spectra were recorded in a three electrode spectroelectrochemical cell in situ during continuous potential cycling of a BBL coated germanium reflection element in contact with the electrolyte solution under applied potential. In contrast to most of the other conjugated polymers, the polymer shows four reversible redox reactions during n-doping, corresponding to five different forms of BBL. From the spectral response, a reduction scheme insulator to conductor to insulator to conductor to insulator was found.     

Nano-structured Langmuir–Blodgett mixed films of titanyl(IV) phthalocyanine and bis(neopentylimido)perylene: Unique degree of miscibility

Langmuir and Langmuir–Blodgett (LB) films of mixed titanyl(IV) phthalocyanine (TiOPc)–bis (neopentylimido)perylene (BNPTCD) were fabricated and characterized. The surface pressure–area isotherms (π–A) of the mixed Langmuir films were recorded and revealed an unusual expansion of the surface area per molecule. The expansion is attributed to the interpenetration of the BNPTCD in the space available between adjacent Pc macrocycles preventing molecular stacking and forcing the expansion. This effect is a result of the high degree of mixing between species in the floating monolayer. This assumption was further supported by means of surface enhanced Raman scattering (SERS) mapping technique that proved the absence of large segregated domains in the LB film, in other words, the absence of phase separated regions, in agreement with a unique degree of miscibility.     

High-pressure study of one-dimensional phthalocyanine conductor,NiPc(AsF6)0.5

NiPc(AsF₆)_0.5 is a two-band system, in which a narrow 3d band is located just below the Fermi level of the π band. This compound undergoes a metal-insulator transition at about 50 K. The nonmetallic state below 50 K is regarded as the Anderson localization caused by a small amount of randomly distributed 3d holes (Ni³⁺). High pressure lifts up the 3d band and causes the gradual charge transfer from 3d to π bands, which enhances the randomness of Ni³⁺ distribution. High-pressure experiments of X-ray diffraction, electrical resistivity and thermopower show that high pressure expands this nonmetallic phase to the high-temperature region in the P-T phase diagram. This extension is consistent with the enhancement of the randomness of Ni³⁺ distribution.     

9,10-Bis(phenylethynyl)anthracene-based organic semiconducting molecules for annealing-free thin film transistors

New anthracene-containing conjugated molecules have been synthesized through Stille coupling reaction. 2,6-Dibromoanthracene-9,10-dione was reacted with ethynylbenzene or 1-ethynyl-4-hexylbenzene to yield 2,6-dibromo-9,10-bis(phenylethynyl)anthracene 4 and 2,6-dibromo-9,10-bis((4-hexylphenyl) ethynyl)anthracene 5. Tributyl(5-hexylthiophen-2-yl)stannane was coupled through Stille reaction to generate two anthracene-based X-shaped molecules. They exhibit good solubility in common organic solvents and good self-film-forming properties. The semiconducting properties of the two molecules were evaluated in organic thin film transistors (OTFTs). Two conjugated molecules 7 and 8 exhibit fairly high charge carrier mobilities—as high as 0.010–0.014 cm² V^?1 s^?1 (I_on/I_off = 1.27 × 10⁷ to 4.38 × 10⁶) without thermal annealing process. The X-shaped molecules result in easy crystallization and densely cover the surface of a dielectric layer. This helps in attaining good network interconnection for the carrier transport channel, which is responsible for the relatively high carrier mobility in solution-processed OTFT.     

Synthesis and characterization of a new poly(aryl ether ketone) containing zinc phthalocyanine

A novel poly(aryl ether ketone) (PAEK) copolymer with metallophthalocyanine units was synthesized by the reaction of PAEK containing dicyanophenyl with excess amounts of 1,2-dicyanobenzene and zinc chloride in quinoline. This copolymer exhibits high glass transition temperatures and excellent thermal stability. This copolymer shows strong optical absorption in the visible region, and exhibits strong blue photoluminescence. Furthermore, this polymer can form differently aggregated structures in chloroform with the addition of 4,4′-bipyridine (Bipy). In particular, when polymer was mixed with 4 equiv. of Bipy, a uniform cotton like superstructure was observed. These results indicated that the axial coordination of zinc phthalocyanine and Bipy plays an important role in controlling the polymer morphologies obtained by the addition of Bipy to solutions of the polymer in CHCl₃.     

Luminescent properties of poly(alkyl methacrylate) polymer films modified with strongly polar phthalocyanine

The fluorescence of strongly polar water-soluble phthalocyanine (2,3,9,10,16,17,23,24-octa-[(4-carboxylate)-phenoxy]phthalocyanine) and styrene-alkyl (meth)acrylate latex copolymers either unmodified or phthalocyanine-modified is studied with the use of emission spectroscopy in the excitation wavelength range of 240?C330 nm. The drop in the fluorescence intensity upon modification of the polymer with phthalocyanine is determined by a possible decrease in the ordering of the hexagonal polymer matrix, the interaction between certain phthalocyanine chromophores and the polymer matrix, and the J-aggregation of phthalocyanine in the polymer matrix. The appearance of a band at 490?C510 nm in the luminescence spectrum of the modified polymer is related to the formation of phthalocyanine J-aggregates in the polymer matrix.     

State of the art electrical discharge machining (EDM)

Electrical discharge machining (EDM) is a well-established machining option for manufacturing geometrically complex or hard material parts that are extremely difficult-to-machine by conventional machining processes. The non-contact machining technique has been continuously evolving from a mere tool and die making process to a micro-scale application machining alternative attracting a significant amount of research interests.In recent years, EDM researchers have explored a number of ways to improve the sparking efficiency including some unique experimental concepts that depart from the EDM traditional sparking phenomenon. Despite a range of different approaches, this new research shares the same objectives of achieving more efficient metal removal coupled with a reduction in tool wear and improved surface quality.This paper reviews the research work carried out from the inception to the development of die-sinking EDM within the past decade. It reports on the EDM research relating to improving performance measures, optimising the process variables, monitoring and control the sparking process, simplifying the electrode design and manufacture. A range of EDM applications are highlighted together with the development of hybrid machining processes. The final part of the paper discusses these developments and outlines the trends for future EDM research.