Group transport properties

The effect of the substituents on chain mobility and chain packing has been related to the gas transport properties [209]. Role of symmetry of methyl group placement on bisphenol rings in PES shows the permeability coefficients in the following order ... 

The gas sorption and transport properties also depend on the bisphenol connector groups [210]. The permeability coefficients for all gases rank in the order ... 

Because of the inherent technical difficulties, investigations of transport properties in molten salts are much less common than those of aqueous solutions. However, interpretation of the phenomena seems to be even simpler in molten salts where water is not involved. Molten salt systems are considered to be the simplest liquid electrolytes. Data have been compiled largely due to the great efforts of the Janz group." "... 

Finally, we note that the idea of manipulating transport properties of molecular junctions by the modification of a master rod with electron-withdrawing or -donating groups was demonstrated before, experimentally [49] and theoretically... 

However, a phase separation problem in the above two-component system may affect the device stability. To overcome the problem, Mullen and coworkers [322] introduced triphenylamine groups as side chains at the PF backbone. The triphenylamine substituents simultaneously improve the hole-transport properties of PF (facilitating the injection of holes),... 

The tuning of electron injection and transport in PF has been undertaken by Shu s group [354], who introduced electron-deficient oxadiazole units as pendant groups in fluorene copolymer 257. The introduction of oxadiazole units into the PF can potentially improve the electron transport properties of the polymer, while their bulkiness can help to suppress aggregation effects (Chart 2.68). 

Introducing heteroaromatic moieties (mainly with N and, to a lesser extent, with O and S) in the backbone of the polymer or as a pendant group, can substantially modify the LUMO level of the materials, improving their electron-transport properties and facilitating electron injection in PLEDs, but the efficiencies still lag behind the other systems. 

An interesting series of high Ts HTMs based on novel indolo[3,2-b]carbazoles has been discovered by the Xerox group [85]. These compounds not only showed the desired hole transport properties and high Ts of 164°C but also display an unusual atropisomerism with two discrete trans- and U.v-rotational isomers (Scheme 3.14), which greatly improves their tendency to form stable amorphous glasses. 

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