Light switch effect

Molecular electronics, class II mixed-valence complexes, 41 303-304 Molecular light switch effect, 43 148 Molecular mechanisms, cobalt(III) hexaamines, 35 119-120 Molecular orbital calculations... 

The data concerning [Rn(phen)2(dppz)] + nicely illustrate the concept of molecnlar light switch (dppz for 28). When the complex is bonnd to DNA, the excited-state lifetime is approximately 200 ns, whereas withont bonnding, it is only 200 ps. This light-switch effect provides the basis for a valuable photophysical probe of nucleic acids. Luminescent characteristics of the complexes bonnd to DNA can also be used to illustrate the chiral discrimination associated with binding to the right-handed hehx. Direct oxidation of... 

Jenkins, Y. Friedman. A.E. Turro. N.J. Barton, J.K. Characterization of dipyridophenazine complexes of ruthe-nium(ll) The light switch effect as a function of nucleic acid sequence and conformation. Biochemistry 1992. 31, 10809. 

Interactions with DNA Light-Switch Effect and Phototherapy... 

Light Switching Effects of Polymer/(Liquid Crystal) Composite Systems T. Kajiyama, H. Kikuchi, J.C. Hwang, A. Miyamoto, S. Moritomi,... 

Light Switching Effects of Polymer/(Liquid Crystal) Composite Systems... 

The photoinduced phenomenon where the change in refractive index is proportional to the second order term of applied voltage is called an electrooptical Kerr effect. Kerr cells of liquid or solid transparent media can be used together with polarizers to transmit or block light, depending on whether an electric field is applied or not. Such light switches have many uses in laser technology. 

Apart from the liberation of electrons from atoms, other phenomena are also referred to as photoelectric effects. These are the photoconductive effect and the photovoltaic effect. In the photoconductive effect, an increase in the electrical conductivity of a semiconductor is caused by radiation as a result of the excitation of additional free charge carriers by the incident photons. Photoconductive cells, using such photosensitive materials as cadmium sulphide, are widely used as radiation detectors and light switches (e.g. to switch on street llghtiug). 

MLCs also have their place in optical applications, mainly as so-called polymer-dispersed LCs (PDLCs). A PDLC constitutes a microemulsion of an MLC in a film of a conventional (nonPLC) polymer. In the switched off state the MLC and the polymer have different refractive indices, dispersed MLC droplets (not unlike to the islands in PLCs) scatter light quite effectively, and the film is opaque. Then an external electric field is applied, for instance across a capacitor-like metal coating on both sides of the film. The director in all MLC droplets becomes the same. One can choose the MLC + polymer pair so that the refractive index along the director is the same as that of the host polymer. In that case the film in the electric field becomes transparent. Switching the field off and on, one has a light valve with a fairly large area. 

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