Azobenzenes chromophore applications

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

Chen et al. reported novel photoswitches using C2-symmetric dibenzo-suberane-based helicenes with a tetraline-based fragment. Photoisomerization of the diastereomerically pure (P)-from (34) led to virtually exclusive formation of the (M )-form (35) at 290 nm irradiation. Upon 330 nm irradiation, (35) isomerized to (34). This photoswitch in a nematic liquid crystal was applicable to a cholesteric mesophase with modulated pitches, reversible helical senses, and a switch memory of ternary logic. Furthermore, the helicene (36)-(39) with bis-azobenzene chromophores acted as highly diastereoselective chirochromic (92 8 to 3 97) and photo-chromic (>99 <1 to 19 81) switches both in solutions and in the nematic liquid crystal. ... 

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