Molecular charge transport

In moleculady doped polymers, charge transport is carried out by the hole-transporting molecular dopants, usually aromatic amines. The polymer merely acts as a binder. The hole mobiUty is sensitive to the dopant concentrations. For example, the hole mobiUty of... 

Both structures are maintained over thicknesses of up to several micrometers and confer a two-dimensional character to the medium. Charge transport is favored in the direction parallel to the film, that is, perpendicular to the molecular axis. 

The two forms differ by the way they pack, a direct result being the different tilt angle of their molecular axis (24" and 30" for the low-temperature and high-temperature form, respectively). Another important difference is the fact that the inversion center of the molecule coincides with a center of symmetry of the unit cell in the HT form, whereas it does not in the LT form 84J. Direct consequences of this feature have not yet been identified. It will be of course of great interest to know what would be its influence on charge transport properties. 

The above statements are valid for monomolecular layers only. In the case of polymer films with layer thickness into the p-range, as are usually produced by electropolymerization, account must also be taken of the fact that the charge transport is dependent on both the electron exchange reactions between neighbouring oxidized and reduced sites and the flux of counterions in keeping with the principle of electroneutrality Although the molecular mechanisms of these processes... 

Palm, K., Luthman, K., Ros, J., Grasjo, J., Artursson, P. Effect of molecular charge on intestinal epithelial drug transport pH-dependent transport of cationic drugs. J. Pharmacol. Exp. Ther. 1999, 293, 435-443. 

A major barrier to understanding fundamental relationships between molecular architecture, electronic structure, and charge transport in molecular metals derives from our inability to introduce poten-... 

Fig. 6 Dynamic molecular motions can gate DNA-mediated charge transport. Two time constants (5 and 75 ps) are observed for hole transfer from photoexcited ethidium, tethered and intercalated near the end of a 14-base pair DNA duplex, to a base analog, 7-deazaguanine, in DNA. The 5 ps time constant, which is independent of distance between 10-17 A, is due to direct hole transfer, while the 75 ps time constant corresponds to reorientation of the ethidium before hole transfer. Adapted from [96]... 

At a more molecular level, the influences of the composition of the membrane domains, which are characteristic of a polarized cell, on diffusion are not specifically defined. These compositional effects include the differential distribution of molecular charges in the membrane domains and between the leaflets of the membrane lipid bilayer (Fig. 3). The membrane domains often have physical differences in surface area, especially in the surface area that is accessible for participation in transport. For example, the surface area in some cells is increased by the presence of membrane folds such as microvilli (see Figs. 2 and 6). The membrane domains also have differences in metabolic selectivity and capacity as well as in active transport due to the asymmetrical distribution of receptors and transporters. 

Ballmann S, Hieringer W, Seeker D, Zheng Q, Gladysz JA, Gorling A, Weber HB (2010) Molecular wires in single-molecule junctions charge transport and vibrational excitations. ChemPhysChem 11(10) 2256-2260... 

Kushmerick JG, Lazorcik J, Patterson CH, Shashidhar R, Seferos DS, Bazan GC (2004) Vibronic contributions to charge transport across molecular junctions. Nano Lett 4(4) 639-642... 

Blum AS, Kushmerick JG, Pollack SK, Yang JC, Moore M, Naciri J, Shashidhar R, Ratna BR (2004) Charge transport and scaling in molecular wires. J Phys Chem B 108 (47) 18124—18128... 

Keywords Charge transport Electrochemical molecular junctions Electron tunnelling Electron hopping Molecular electronics Photoactive molecular junctions... 

After a brief discussion of fundamentals of charge transport mechanisms, this chapter summarizes and discusses the most significant results obtained by using different junctions and in particular LAJs. In order to facilitate a systematic discussion, we make a functional distinction between non-active and active junctions we will refer to active junctions as those aimed at changing the electrical response by means of an external stimulus acting in situ to modify the molecular electronic structure non-active junctions are those used to measure and compare the electrical properties inherent to the different electronic structure of incorporated molecules, without any modification induced by an external signal. 

---