Photoswitchable materials

Photoswitchable materials could be important components in molecular-scale electronic devices and several new systems have been reported. There have been other investigations of phototropic systems in which light is used to drive a reversible conformational change " or, in the case of liquid crystals, a phase transformation. Such photosystems are of interest for the engineering of microscopic photoactive devices but the subject is still in its infancy and practical devices remain elusive. Much more subtle is the use of light to trigger a change in... 

The selected examples in this chapter demonstrate the success of the development of photoswitchable molecular materials through the rational designs based on the coupling of photochromic moieties into molecules with different functions, such as luminescence, nonlinear optics, liquid crystal, molecular machine, receptor, electrical con-ductor/semiconductor, and many others. It is important to emphasize that photoswitchable materials are not confined only to the selected areas in these examples. With the understanding of both the photoswitching processes and the functional properties at the molecular levels, materials that possess different varieties of photoswitchable functional properties can be readily designed and synthesized. 

Further studies on these systems should stimulate the design of new and more effective photosurfactants in order to achieve a greater active control over the physicochemical properties of interfaces. For further reading on photoswitching materials, see Photoswitching Materials, Supramolec-ular Devices. 

Other applications of photoswitchable materials on SAMs are the UV-controlled complexation of metal ions to the merocyanine isomer of spiro-naphthoxazine-thioethers (Fig. 41a) [214]. The long saturation times for the pure spironaphthoxazine-SAM at complexation with zinc ions is an indication for a densely packed spironaphthoxazine-monolayer, with only a small fraction of open merocyanine isomer due to steric constraints. 

Photostimulation of redox enzymes could transduce recorded optical signals as an amperometric response by their electrical interaction with electrode interfaces. For example, amperometric transduction of recorded optical signals was accomphshed using nitrospiropyran-modified glucose oxidase as photoswitchable material (Fig. 44) [14]. 

Photoswitchable materials molecular entities or supramolecular assemblies, which use light to toggle reversibly between distinct states of the system with markedly different properties [1, 2]. As a consequence of the changes produced at the molecular scale, a significant modification of some of the macroscopic properties of the material are induced. On this basis, many photochromic [3-5], fluorescence [6-8], chirality [9-11], and halochromic [12-14] switches have been reported during the past decades. 

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