Light-switchable optical system

A three-level switching device has been demonstrated in which photochromic properties are used to control electrical properties, and vice versa. Such a system has been realized in the form of thiophene bisphenol [90, 91]. Conversion of the open (8a) to the closed (8b) form of the thiophene was achieved by absorption of 312 nm light, and revered by absorption of 600 nm light. The bisphenol oxidation occurs at +0.735 V (vs. SCE), forming the closed-ring bisquinone, compound 8c. This species has large absorptions at 400 and 534 nm. The optical properties of the quinone phenol couple have previously been used in a bianthrone-based system [87]. The bisquinone (8c) cannot be converted to the open thiophene, and locks the system in the closed form. The thiophene has also been incorporated as a component in two-level molecular switches [99, 128] and switchable molecular wires [30]. 

However, little attention has been focused on this kind of optical interlocked molecular systems despite that a large number of molecular machine systems have been set up for more than a decade. These facts became our impetus to build up light-driven molecular machines with fluorescence output. A cyclodextrin ring can exert micro-environmental changes because of its rigid hydrophobic cavity, and thus affects the fluorescent properties of a fluorophore coming close. As a consequence, CDs may be served as the useful ring component to construct switchable rotaxanes with fluorescent addresses. 

---