Direct read-after write

Perhaps the most remarkable photoswitchable system based on this concept is that shown in 11.55 (Scheme 11.9), which represents a system that is both photo- and electroswitchable. As with 11.53, the open BIS-OH form is electrochemically inert. Photoswitching to the closed form enables the molecule to be oxidised easily to the bis(quinone) BIS-Oq. The quinone form is photochemically inert and cannot revert back to an open form until re-reduced. The system is of interest in the context of information storage applications. It represents a chemical approach to the EDRAW (erase direct read after write) mode... 

Since the developed color of viologens induced by photoreduction is vivid, and a variety of color species can be obtained by changing their chemical structure, it can be expected that there are several kinds of potential applications using photochromic viologens, especially an erasable-direct-read-after-write (EDRAW) media for recording devices with high storage density and reliability. 

The abbreviation DRAW stands for direct read after write. 

The absorbing layer is then protected by a transparent overcoating of crosslinked poly( dimethyl siloxane) elastomer. This will produce a direct read after write, or DRAW, disc that is non-erasable. 

Several types of Direct Read After Write (DRAW) discs on which data can be digitally recorded either once (write-once) or repeatedly (erasable). Initial applications are largely in professional equipment, for example as storage systems for large archieves. 

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