Photoswitch, or photo-electric switch, is a sensor that detects the presence of light or a change in its intensity. Photoswitches are one type of molecular machines, a class of molecules that can be switched between at least two distinct thermodynamically stable forms by the application of an external stimulus. The development of such devices is crucial in the framework of nanotechnology; nowadays, photoswitches are applied in a variety of places from scientific applications to residential light timers. Organic compounds have been deployed as photoswitches and a popular example of it is azobenzene.
A photoswitchable molecule is a chemical that is sensitive in some way to light, e.g. able to turn on retina cells when exposed to light,. Some examples include AAQ, DENAQ, photochromic compounds, azobenzenes, spiropyrans, diarylethenes, fulgides, overcrowded alkenes. For instance, azo compounds can isomerize by absorbing a particular wavelength of light. This photoisomerization transforms the azo group from the trans to the cis form. Novel azo carrying photoswitches are introduced as molecular hinges which can be used in the design of molecular machines and optical devices .
A photo-electric cell is connected to a circuit that measures how much electricity the cell produces and according to the setting of minimum and maximum lux level, the circuit decides and gives the output.
Photoswitches have recently also been used in the generation of three-dimensional animations and images . The display utilizes a medium composed of a class of photoswitches (known as spirhodamines) and digital light processing (DLP) technology to generate structured light in three dimensions. UV light and green light patterns are aimed at the dye solution, which initiates photoactivation and thus creates the 'on' voxel. The device is capable of displaying a minimum voxel size of 0.68 mm^3, with 200 μm resolution, and good stability over hundreds of on-off cycles.
In the field of photopharmacology, photoswitches are used to obtain control over the activity. By including a photoswitch to the drugs, a drug with several states is created, all having their own biological activity. Light can be used to switch between these states, resulting in drugs with remote control over the activity.
The issue of the photoswitch that the reflecting efficiency of the reflecting member may be drastically lowered due to dewing and clouding of the reflecting surface due to a change in the ambient temperature. The dew on the reflecting surface causes a random reflection. In order to avoid the clouding of the reflecting surface, it has been proposed to apply silicon or the like to the surface of the reflecting member. This countermeasure, however, cannot prevent condensing of dew onto the lower part of the reflecting surface. Thus, there are many problems in the prior art.
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- Patent US4437728 - Photo-switch - Google Patents