Ion-radical Approach to Molecular Switches and Modulators

Accumulation and reorganization of information can also be achieved on the basis of cis-trans isomerization of olefins in their ion-radical states. An application of the phenomenon in real electron memory systems was claimed (Todres 2001). For the neutral arylethylenes, conversion from 

If di-arylethylenes are used as electrochromic substances (in media capable of conducting electric current), applying a 10- to 12-V cyclically changing voltage enhances the optical absorption as described earlier. These changes are readily registered and remain constant for at least 2 years. In order to return to the initial state of the system, it is sufficient to apply a near-UV light impulse for just a few seconds. The record-erase cycles can be repeated more than 1000 times with the same capacity. 

Exploiting arylethylenes as bearers of electron memory has the following advantages First, the compounds are commercially available and inexpensive. Second, they work for very long time. Third, transformation of the information recorded is simple and consumes little energy. In other words, creation of electron memory systems through ion-radical route is fruitful. 

Electron transfer is often associated with the conformational changes. For organic ion-radicals the inner reorganization energies remain modest, allowing a fast passage between the different conformations during the electron transfer (e.g., see Bellec et al. 2000). 

Electro-optical modulators are other examples whose efficiency is enhanced in the presence of ion-radicals. These devices are based on the sandwich-type electrode structures containing organic layers as the electron/hole-injecting layers at the interface between the electrode and the emitter layer. The presence of ion-radicals lowers the barrier height for the electron or hole injection. Anion-radicals (e.g., anion-radicals from 4,7-diphenyl-l,10-phenanthroline—Kido and Matsumoto 1998 from tetra (arylethynyl) cyclooctatetraenes—Lu et al. 2000 from bis (1-octylamino) perylene-3,4 9,10-bis (dicarboximide)s— Ahrens et al. 2006) or cation-radicals (e.g., cation-radicals from a-sexithienyl—Kurata et al. 1998 l,l-diphenyl-2-[phenyl-4-A/,A- /i(4 -methylphenyl)] ethylene— Umeda et al. 1990, 2000), all of them are electron or hole carriers. 

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