We survey the current state of models for electronic processes in conducting polymer devices, especially light-emitting diodes. We pay special attention to several processes that have been somewhat neglected in the previous literature: charge injection from electrodes into a polymer sample, mobility of charge-or energy-carrying defects within a single molecule and (more briefly) transfer of carriers between molecules and the interaction between the charge transport and the mesostructure of the polymer. Within all these areas substantial progress has been made in recent years in elucidating the important physics, but further progress is needed to make quantitative contact with experiment.
Molecular electronics based on structures ordered as neural networks emerges as the next evolutionary milestone in the construction of nanodevices with unprecedented applications. However, the straightforward formation of geometrically defined and interconnected nanostructures is crucial for the production of electronic circuitry nanoequivalents. Here we report on the molecularly fine-tuned self-assembly of tetrakis-Schiff base compounds into nanosized rings interconnected by unusually large nanorods providing a set of connections that mimic a biological network of neurons. The networks are produced through self-assembly resulting from the molecular conformation and noncovalent intermolecular interactions. These features can be easily generated on flat surfaces and in a polymeric matrix by casting from solution under ambient conditions. The structures can be used to guide the position of electron-transporting agents such as carbon nanotubes on a surface or in a polymer matrix to create electrically conducting networks that can find direct use in constructing nanoelectronic circuits.
Although extensive studies have been conducted on poly(vinylidene fluoride) (PVDF) because of its ferroelectric, pyroelectric and piezoelectric properties, the effects of inverted monomer units, on the molecular scale properties of this polymer are not fully understood. Therefore, we have used a method combining molecular dynamics with a self-consistent semi-empirical quantum mechanical method to study the effects of both chain length and monomer inversion on the electronic properties of individual PVDF chains, such as the dipole moment and the polarizability. The effects of monomer inversion on the infrared spectra are also discussed. Our results suggest that alpha and beta polymorphs of PVDF have dipole moment per monomer unit that varies (increases for beta-PVDF and decreases for alpha-PVDF) with the chain length but converges to a nearly constant value for chain lengths greater than a certain value, whereas chain length does not seem to produce any significant effect on molecular polarizability of both polymorphs. Our calculations also suggest a decrease of the dipole moment with increasing inversion monomer defect concentration but no significant effect has been predicted for molecular polarizability, except when two or more isolated defects are present in the same chain. The presence of monomer inverted defects decreases the intensity of the infrared peaks attributable to defect-free chains and gives rise to new peaks. The number and frequency of the defect peaks depends both on the isolated defect concentration and molecular chain structure.
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