Optical Memories and Switches

For a photochromic material to be of any use in optical memories it must meet the minimum requirements in the following physical properties  

Of those properties on the list, the most difficult to attain is a non-destructive readout procedure. Two approaches have been adopted to overcome this problem.  

Detect the two forms, A (colourless) and B (coloured), using light of a lower energy than the UV-Visible light used for the interconversion (A into B, B into A). The readout can be measured as the difference in the reflecting light intensity of the laser e.g. diode), or by fluorescence or infrared absorption signals in the two 

Involves two reversible processes. In the first, irradiation with light in the UV-Visible range causes the interconversion of A and B. hi the second process a photon, an electron or a proton is used to prevent the interconversion of A and B by transforming them into stable A and B products. The two forms in the system can therefore be locked or unlocked.  

Near-held optics, in which recording density depends only on the size diameter of the probe tip aperture  

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S. Nespurek, Molecular optical memories and switches based on photochromic dihydropyridines, BioSystems, 27, 213-218 (1992). 

Diarylethenes are one of the most promising photochromic materials for such purposes as molecular optical memories and switches, because of their excellent thermal stability and fatigue-resistant nature [51]. A chiral dithienylethene has the potential for non-destructive readout by detecting optical rotation at wavelengths longer than its own absorption band. However, it is not a simple task to achieve appreciable stereoselectivity in solution-phase photocyclization of dithienylethenes, even for those with chiral substituents [52-54]. In this regard, a... 

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