Molecular optoelectronic devices

Photochromic processes are often observed both in solution and in the solid state, thus making for facile incorporation of photochromies in films, in membranes, and as dopants in host matrices—prerequisites for the construction of molecular optoelectronic devices. Section 2.3.1 focuses on the materials and supramolecular systems prepared from photochromic systems. For more comprehensive descriptions of the basic photochemical processes the reader is referred to any of the numerous reviews on the subject [47, 51, 89, 159-162]. 

Electrical behavior of molecular optoelectronic devices the role of chemistry in signal generation... 

ELECTRICAL BEHAVIOR OF MOLECULAR OPTOELECTRONIC DEVICES THE ROLE OF CHEMISTRY IN SIGNAL GENERATION... 

The signal-triggered functions of these molecular assemblies have to be first characterized in bulk solution. Then, extensive efforts have been directed to integrate these photoswitchable chemical assemblies with transducers in order to tailor switchable molecular devices. The redox properties of photoisomerizable mono-layers assembled on an electrode surface are employed for controlling interfadal electron transfer [16]. Specifically, electrical transduction of photonic information recorded by photosensitive monolayers on electrode supports can be used in developing monolayer optoelectronic systems [16-19]. Electrodes with receptor sites exhibiting controlled binding of photoisomerizable redox-active substrates from the solution [20] also allow the construction of molecular optoelectronic devices. 

Conformational transitions and electron redistribntion on pressure results in changes of the ion-radical properties and this is essential for optoelectronic devices. Pressure is the thrust distributed over a surface. The most important results of compression are reduction of molecular volumes and conformational changes of organic componnds. Spectral changes of solids are also termed piezo-chromism. Let ns consider several relevant examples of piezochromism. 

The diverse properties of organic molecular materials, of which the polymers are amongst the primary ones, will, without doubt, be intensively developed in the future. Photosensitive polymer semiconductors with pre-given properties and a broad spectrum of application will be created for various optoelectronic devices. 

In molecular beam epitaxy (MBE) [317], molecular beams are used to deposit epitaxial layers onto the surface of a heated crystalline substrate (typically at 500-600° C). Epitaxial means that the crystal structure of the grown layer matches the crystal structure of the substrate. This is possible only if the two materials are the same (homoepitaxy) or if the crystalline structure of the two materials is very similar (heteroepitaxy). In MBE, a high purity of the substrates and the ion beams must be ensured. Effusion cells are used as beam sources and fast shutters allow one to quickly disrupt the deposition process and create layers with very sharply defined interfaces. Molecular beam epitaxy is of high technical importance in the production of III-V semiconductor compounds for sophisticated electronic and optoelectronic devices. Overviews are Refs. [318,319],... 

Fabrication is difficult, but the large-scale assembly of nanoscale building blocks into either devices (e.g. molecular electronic, or optoelectronic devices), nanostructured materials, or biomedical structures (artificial tissue, nerve-connectors, or drug delivery devices) is an even more daunting and complex problem. There are currently no satisfactory strategies... 

Coronado, E. and Palomares, E. Hybrid molecular materials for optoelectronic devices, J. Mater. Chem., 2005, 15, 3593-3597. 

Achievements in the field of organic conductors and superconductors have promoted the development of the field of molecular electronics as well. The latter is a nascent field of research, suggesting the use of organic molecules with the tunability of their electronic structure, instead of conventional inorganic microelectronics. It has been suggested that molecular electronic devices could utilize a variety of optoelectronic and conductivity phenomena of organic substances at the nanometer level. Whereas the conductivity and superconductivity of organic metals is a result of bulk electrical behavior of lower-dimensional systems, molecular electronics deals... 

Recently, low-temperature routes have been sought for by decomposition of organometallic complexes with tellurium-containing ligands. The optoelectronic devices normally require the material to be used as thin films. They are fabricated with special methods, such as molecular beam epitaxy, metal-organic chemical vapour deposition, or atomic layer deposition. 

Recently there has been a great deal of interest in nonlinear phenomena, both from a fundamental point of view, and for the development of new nonlinear optical and optoelectronic devices. Even in the optical case, the nonlinearity is usually engendered by a solid or molecular medium whose properties are typically determined by nonlinear response of an interacting many-electron system. To be able to predict these response properties we need an efficient description of exchange and correlation phenomena in many-electron systems which are not necessarily near to equilibrium. The objective of this chapter is to develop the basic formalism of time-dependent nonlinear response within density functional theory, i.e., the calculation of the higher-order terms of the functional Taylor expansion Eq. (143). In the following this will be done explicitly for the second- and third-order terms... 

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