One-dimensional molecular systems

A. Orientational-Tunneling Model of One-Dimensional Molecular System... 

Therefore, if one indeed wants to use DNA as an electrical molecular wire in nanodevices, or as a model system for studying electrical transport in a single one-dimensional molecular wire, then there are a few possible options. One option is to use doping by one of the methods that are described... 

It is evident that two hydrogen bonds between adjacent molecules and the chirality of molecule contribute to one dimensional molecular alignment in spite of the strong dipole-dipole interactions and that -conjugated system of DAD molecule extend from amino groups to cyclobutenedione ring enhance second order nonlinearity of DAD molecular crystal. 

During the past decade there has been very intense experimental and theoretical research on the physics and chemistry of polymeric materials. This work has led to the discovery of a great number of organic and inorganic crystals built from polymers or molecular stacks which have a quasi-one-dimensional electronic system and exhibit fascinating electric, magnetic, etc. properties. Other polymers have proved to play a fundamental role in the biosciences. 

If a further donor or acceptor group is added to the one-dimensional ir systems above, but Cjv symmetry (as for p-nitroandine) is retained, molecules such as 3,5-dinitroaniline result. Formally, a doubly degenerate CT from the donor to the two acceptors occurs. The one-dimensional approximation is no longer valid and the off-diagonal tensor elements Py y and Pyy may become significant. These arise from low-lying CT bands with transition dipoles perpendicular to the molecular C2 axis (z axis). The two-level contributions to the SHG polarizability for off-diagonal elements can be written in the form (56) and (57),... 

The quasi one-dimensional molecular conductor (RiRjDCNQIjjCu shows novel electronic properties discussed in the last section. With increasing pressure the metallic state becomes unstable undergoing a metal-insulator transition. In addition the system undergoes a metal-insulator-metal re-entrant transition with lowering temperature in a narrow pressure range above a critical pressure of about 0.1-0.5 kbar (10-50 MPa) [79]. 

However, there are essential differences between the Lorentz gas model and IS structures in many-dimensional molecular systems. The most obvious difference is the size distribution of basins. In the Lorentz gas model, the size of unit cells is identical but the basin size, as well as the depth of potentials, of molecular systems is believed to range quite broadly, and possibly distributed in a self-similar way, reflecting that local potential minima increase exponentially as a function of the system size. As a result, one expects that the diffusion among multibasin structures bears different characters. The situation of the latter is... 

As a result of the second-order effect, also large C4, 4 2 monocycles are expected to be acetylenic as is explained by the Peierls distortion that is seen in one-dimensional electronic systems with periodic potentials [35b-e]. This effect is associated with the distortion of the potential energy surface to lower the total energy of the system through electron-phonon coupling [35b]. For a molecular system, the same effect is also referred to as the second-order Jahn Teller (SOJT) effect that leads to the vibrational-mode... 

The conversion of reactants is illustrated by the dehydration-polymerization of 2-isopropanol adsorbed on K- and Cs-ZSM-5 zeolites as followed by 1JC-NMR. On the other hand, the polymerization of ethylene shows a clear-cut difference between three-dimensional channel systems (ZSM-5 and ZSM-11) able to promote the molecular traffic of reactants and on one-dimensional channel systems (ZSM-48) where some unreacted ethylene is still detected after polymerization. 

A sized pores is very slow, which implies that counter-diffusion will not occur at all in these systems, and that intraporous reactions cannot occur at an appreciable rate. The use of molecular sieves with one-dimensional channel systems as catalysts therefore results in residual non-shape-selective catalytic activity caused by the outer surface of the crystallites. 

It should be emphasized, however, that likely in none of these studies was the zeolite material of such an ideal structure as implied in data analysis. In this respect, experimental studies with artificially created single-file systems [127-129] may provide a much higher rehability of the pre-supposed structural features. A treatise on the substantial deviations of the real structure, with particular emphasis on the consequences for ideal host systems for single-file diffusion as evidenced by optical techniques, is given in [95]. Irrespective of these limitations, however, a number of peculiarities of catalytic reactions in zeolites with one-dimensional channel systems are most Ukely to be attributed to the special conditions of molecular transport and molecular arrangement imder single-file conditions. 

Mukhopadhyay et al. first used LB films of specially substituted phthalocyanine molecules to sense toluene vapor based on the changes in the electrical conductivity [9]. Phthalocyanine and porphyrin derivatives are p-type semiconductors. The interaction with n-electron systems can lead to a cofacial orientation of the nucleus, resulting in a one-dimensional semiconducting system. The exposure to the VOCs may change the cofacial molecular orientation and, as a consequence, the conductivity. However, the interaction between the VOCs and the sensitive molecules is not very strong, as these VOCs are not strong electron donors or electron acceptors. A very low conductivity of 10 to 10 S/cm was usually measured when the sensitive layers were exposed to the VOCs, which is difficult to be detected. Therefore, in most cases, the mass transduction and UV-vis absorption method were adopted to detect the presence of organic vapors. 

In molecular conductors, if we assume a strictly one-dimensional ideal system (no interrupted strands due to some impurities or disorder) with identical point sites (no internal degree of vibrations or librations), in a rigid lattice approximation (no modulation of the transfer integral by the lattice phonons), we observed a bandwidth, whose density of states N(E) (Fig. 3), is typically A = 41 < 1 eV [17]. 

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