Gravimetric studies of the sorption of toluene and propanol by copper phthalocyanines

Sorption isotherms of toluene and n-propanol were determined at 25°C on well-characterised samples of the α and β forms of copper phthalocyanines, the measurements being made with a Cahn RG electrobalance and a McBain-Bakr spring balance. A study of sorption hysteresis was undertaken with each solid—vapour system. The work demanded reliability of instrumentation for the measurement of small changes in mass over long periods of time (up to several months).The toluene isotherm data obtained with the sample of β-copper phthalocyanine appear to be fairly straightforward to interpret: the solid—vapour interaction is relatively weak and hysteresis is confined to the capillary condensation range. On the other hand, the sample of α-copper phthalocyanine underwent considerable ageing when exposed to toluene vapour; the toluene isotherms show low-pressure hysteresis and indicate strong solid—vapour interaction.The initial n-propanol adsorption isotherms on the β-copper phthalocyanine is Type III in character, but desorption resulted in the strong retention of alcohol molecules at very low pressure. The uptake of n-propanol by the α-copper phthalocyanine was much larger than that given by the β form and appreciable ageing occurred on exposure of the sample to n-propanol vapour.These results reveal that the β-copper phthalocyanine sample was more stable when exposed to toluene or n-propanol than the α form (although the original surface areas were similar). Toluene adsorption appears to be restricted to the crystal surface of the β-copper phthalocyanine, whereas the sorption of toluene and n-propanol by the α form involves penetration within the pigment aggregates. The irreversible sorption of n-propanol may be partly due to slow intercalation.     

Reliable far-infrared photoconductivity method to identify a variety of residual donors in epitaxial GaAs

The chemical identity of unintentional contaminants in ultra-high purity eipitaxial GaAs and related semiconductor crystals can be distinguished by submillimeter wave magneto-spectroscopy at low temperature. An improved method of identifying hydrogen-like donors such as sulfur, silicon, selenium and germanium has been developed for the purpose of correcting some mistaken identifications that have been published during the past ten years. The new method requires the development of an experimental “signature curve” for each contaminant by measuring the energy of its 1s to 2p (m=?1) transition at several values of magnetic field intensity. The energy of this transition at a given magnetic field intensity is different depending upon the nucleus to which the electron is bound in the 1s state. The validity of the improved method was tested by means of transmutation doping.     

Millimeter and submillimeter wave measurements of complex optical and dielectric parameters of materials

These two promising millimeter wave materials were found to exhibit one order of magnitude higher absorption coefficient than the common low-loss ceramics such as alumina, fused silica and beryllia. A modular, polarizing, dispersive Fourier transform spectrometer capable of operating over the range 5 mm to 0.004 mm was used to provide a continuous spectrum of the refractive index and absorption coefficient to an accuracy of five decimal places and less than 1 percent, respectively.     

Palladium-catalysed cross-coupling reactions in the synthesis of some high polarizability materials

Liquid crystal materials of high optical anisotropy consist of moieties of high electron density in conjugation with each other along the molecular length. Such structures are conducive to convergent synthesis methods. Here we report the synthesis of a range of novel materials by the strategic use of palladium-catalysed cross-coupling methods. In addition to the traditional use of bromide and iodide leaving groups, invaluable use of the triflate leaving group and the importance of selective cross-coupling methods using both arylboronic acids and alkynylzinc chloride derivatives is illustrated. This systematic methodology allows the separate synthesis of the appropriate sub-units that can be efficiently coupled together to provide high overall product yields.     

The Synthesis and Liquid Crystal Properties of Some 2,5-Disubstituted Pyridines

The synthesis is reported of fifteen three-ring 2,5-disubstituted pyridines and two pyridine-N-oxides where the pyridine rings carry a variety of alkyl, aryl, cyclohexyl, cyclohexylethyl and fluorinated-aryl substituents. The mesomorphic transition temperatures for these compounds have been measured; all the compounds show enantiotropic phases. The different substituent effects are discussed and comparisons are made with previous work on analogous systems where the hetero-function is replaced by C-F.