Molecular crystals optical/electrical properties

These results illustrate that electrochemical techniques can be employed to synthesize a vast range of [Si(Pc)0]n-based molecular metals/conductive polymers with wide tunability in optical, magnetic, and electrical properties. Moreover, the structurally well-defined and well-ordered character of the polymer crystal structure offers the opportunity to explore structure/electro-chemical/collective properties and relationships to a depth not possible for most other conductive polymer systems. On a practical note, the present study helps to define those parameters crucial to the fabrication, from cheap, robust phthalocyanines, of efficient energy storage devices. 

One of the most specific and unique features of low-molecular liquid crystals is their ability for orientation in external fields — mechanical, electric and magnetic. It is this property that establishes wide capabilities for technical application of liquid crystals. Today electric and magnetic optics of liquid crystals are an independent and useful for practics branch of the physics of the condensed state of matter 42 43 ... 

After 14 years on the faculty of Imperial College, Jacobs moved from London, England, to London, Ontario, where his research program focused on the optical and electrical properties of ionic crystals, as well as on the experimental and theoretical determination of thermodynamic and kinetic properties of crystal defects.213 Over the years his research interests have expanded to include several aspects of computer simulations of condensed matter.214 He has developed algorithms215 for molecular dynamics studies of non-ionic and ionic systems, and he has carried out simulations on systems as diverse as metals, solid ionic conductors, and ceramics. The simulation of the effects of radiation damage is a special interest. His recent interests include the study of perfect and imperfect crystals by means of quantum chemical methods. The corrosion of metals is being studied by both quantum chemical and molecular dynamics techniques. 

In the last few years, several workers have analyzed charge density distribution in molecular crystals with non-linear optical (NLO) properties [71-74]. The NLO response can, in principle, be explained by an anharmonic distortion of the electron density distribution due to the electric field of an applied optical pulse. The polarization P induced in a molecule is... 

Finally, soHd-state physicists make use of molecular crystals when they wish to understand certain aspects of soUd-state physics better theoretically and experimentally. Weak intermolecular bonding forces, electrical conductivity with a very narrow handwidth, large anisotropies in their electrical, optical and magnetic properties, one-dimensional conductivity. Unear excitons, and linear magnetic ordering states are best studied in these material classes. 

In the coming years, excitons in disordered systems and strongly-coupled excitons will be a focus of attention. In mixed crystals consisting of two components, the guest molecules can be included into the exciton band of the host, i.e. amalgamated. The influence of such an amalgamation on the electrical, optical, and mag-nehc properties of the mixed crystals is an interesting, old, but still current research topic in the physics of molecular crystals [43]. 

Liquid crystals (LCs) represent an intermediate state of matter between the solid and liquid phases, often referred to as the fourth state of matter, and exhibit the regularity of crystalline solid and the fluidity of isotropic liquid [1-4], The unique thermal, mechanical, optical, and electrical properties of LCs originate from the molecular self-organization facilitated by weak intermolecular interactions, which is sensitive to external stimuli. Stimuli-responsive LCs are at the forefront in the development of electro-optic devices such as LC displays (LCDs) and continue to attract great interest in view of both fundamental research and practical applications. 

Besides aligning liquid crystals, external electric fields can also change the orientational order and thus the electro-optical properties of liquid crystals. When the long molecular axis of a liquid crystal molecule, whose anisotropy of polarizability is positive, is parallel to the applied field, the potential of the molecule is low. Thus the applied field suppresses the thermal flue-mation and increases the order parameter. Now we discuss how the orientational order of a nematic liquid crystal changes with applied fields. Using the Landau-de Gennes theory, the free energy density of a liquid crystal in an electric field (when the liquid erystal director is parallel to the field) is [4]... 

Development of new liquid crystalline (LC) polymeric materials has been a subject of intense interest because of the combination of unusual optical, electrical, and magnetic properties of low-molecular-weight liquid crystals and the mechanical performance and processibility of polymers. Application areas of LC polymers are very diverse, from engineering plastics to LC displays and erasable compact disks. However, the development of conducting and liquid crystalline polymers went on separately in the past in spite of the similarity of the molecular structures of typical main-chain liquid crystals and some conductive polymers. 

Any study of hquid crystals mrrst concern itself with both the chemistry and physics of this state of matter. The most irrrportant areas of hquid crystal chemistry are the relationship between molecular structure and the properties of the various hquid crystal phases, the many methods for syrrthesising hquid crystahine compotmds, arrd the behaviom of amphiphilic molecrrles arrd polymers that form hquid crystal phases. Liqrrid crystal physics concerrtrates on the mechanical, electrical, magnehc, and optical properties of the various hqttid crystalline phases, the different theorehcal models that describe both hquid crystal phases arrd the transitions between them, and the behaviorrr of hqttid crystals in technical devices. 

The selected examples in this chapter demonstrate the success of the development of photoswitchable molecular materials through the rational designs based on the coupling of photochromic moieties into molecules with different functions, such as luminescence, nonlinear optics, liquid crystal, molecular machine, receptor, electrical con-ductor/semiconductor, and many others. It is important to emphasize that photoswitchable materials are not confined only to the selected areas in these examples. With the understanding of both the photoswitching processes and the functional properties at the molecular levels, materials that possess different varieties of photoswitchable functional properties can be readily designed and synthesized. 

The existence or nonexistence of mirror symmetry plays an important role in nature. The lack of mirror symmetry, called chirality, can be found in systems of all length scales, from elementary particles to macroscopic systems. Due to the collective behavior of the molecules in liquid crystals, molecular chirality has a particularly remarkable influence on the macroscopic physical properties of these systems. Probably, even the flrst observations of thermotropic liquid crystals by Planer (1861) and Reinitzer (1888) were due to the conspicuous selective reflection of the helical structure that occurs in chiral liquid crystals. Many physical properties of liquid crystals depend on chirality, e.g., certain linear and nonlinear optical properties, the occurrence of ferro-, ferri-, antiferro- and piezo-electric behavior, the electroclinic effect, and even the appearance of new phases. In addition, the majority of optical applications of liquid crystals is due to chiral structures, namely the ther-mochromic effect of cholesteric liquid crystals, the rotation of the plane of polarization in twisted nematic liquid crystal displays, and the ferroelectric and antiferroelectric switching of smectic liquid crystals. 

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