Electronic transport behavior is analyzed in a model polytetraphenylbenzidine (PTPB) hole transport polymer in which electroactive tetraphenylbenzidine sites are covalently bonded within the polymer main chain. Time-of-flight (TOF) techniques are used to measure the hole drift mobility as a function of electric field and temperature. The TOF data are parametrized using the phenomenological model originally proposed by Gill. For comparative purposes, the disorder model developed by the Marburg group is also used to analyze the data. Transport of holes in PTPB is demonstrated to occur via hopping among the TPB functional units. A pattern of convoluted field and temperature-dependent features, now known to be shared by a broad class of disordered molecular materials, is revealed by the TOF data. Thin solid film electrochemical techniques are applied in parallel with the TOF technique to independently obtain hole diffusion coefficients (Dz ) in thin films of PTPB. As a unique consequence of this comparison, it is established that mobilities, computed from solid-state hole diffusion data using the Einstein relation, converge with zero-field extrapolated TOF mobilities over a wide temperature range when the extrapolation is computed from log p vs E'/ plots. Therefore, the functional dependence of the logarithm of the drift mobility on the square root of field, a much discussed general feature of electronic transport in disordered molecular materials, is demonstrated to persist through the critical low-field limit. At the same time it is demonstrated that the contribution of thermally driven diffusive broadening, which can now be calculated directly from the independently determined electrochemical hole diffusion coefficients, makes an insignificant contribution to the experimentally observed width of the time-offlight transit pulse. A comparison of the PTPB data with analogous TOF data on solid solutions of TPD (the functional unit in PTPB) dispersed in polycarbonate is described. The observation that hole drift mobilities in PTPB are an order of magnitude smaller than those in the corresponding TPDpolycarbonate solid solution is discussed in terms of disorder and steric constraints. 1992 The American Physical Society 6706 ABKO%ITZ, FACCI, LIMBURG, AND YANUS 46 ( J

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The effect on electrochemical behaviour and electronic charge distribution was examined for a series of 12 vinyl aromatic compounds having the following structural variations : (a) number of cyano-groups attached to the vinyl double bond, (b) substitution para to the vinyl group, and (c) separation between para-substituent and the vinyl group. The radical anion formed in the first one-electron reduction step can either accept a second electron or undergo an irreversible dimerization. Oxidation waves were seen only with those compounds having an amino nitrogen atom para to the vinyl group. Trends in half-wave potentials caused by variation in structure are correlated by means of the Hammett-Zuman and molecular orbital approaches. Due to the strong electron-withdrawing power of the cyano-substituted vinyl group, considerable intramolecular donor-acceptor interaction occurs between the ends of the molecules. This is seen in the measured molecular dipole moments and reflected in the nitrile stretching frequencies and proton chemical shifts. Finally, the efficiences for generation of charge carriers in the compounds as measured by xerographic discharge are related to their solution reduction potentials.THE characterization of the series of mono-, di-, and tricyanovinyl aromatic compounds (1)-(XII) receives its impetus from the possibilities for electrophotographic application shown by members of this class of com-pounds1 Recent reports from these laboratories describe changes of orders of magnitude in charge carrierx -CN

I t is shown that optically active methyl-a-naphthylphenylsilyldiphe~~ylcarbinol and optically active methyl-a-naphthylphenylsilylmethylphenylcarbinol undergo highly stereoselective rearrangements to the isomeric silyl ethers. Both rearrangements involve retention of configuration a t the asymmetric silicon center. The silylmethylphenylcarbinol is also shown t o undergo retention of configuration with complete stereoselectivity a t the asymmetric carbon center, regardless of the catalyst or solvent employed. The use of nuclear magnetic resonance for determining the proportions of the diastereomers is described, as are the syntheses of a number of asymmetric silicon compounds.Canadian Journal of Chemistry. V o l u m e 45, 1231 (1967)

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