Photoresponsive materials

In addition to electric potential, light can also be used to trigger switching properties of surfaces and polymers. Application of ultraviolet (UV) light to these materials may result in reversible changes in characteristics such as hydrophilic-ity/hydrophobicity, structural arrangement, and shape. Commonly utilized photoresponsive materials include azobenzene molecules, spiropyran molecules, and shape-memory polymers. 

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Now, application in 3D optical storage memoiy and lasers devices or infrared sensitive spiropyranes, are the focus of investigation in optical technology, which has raised interest in these photoresponsive materials. 

Capillary effects Surface tension y, thermal, electrical (electrocapillarity), surface tension gradients Vy, chemical, thermal, electrical, optical Capillary pressure difference (e.g., Sammarco and Bums 1999) (e.g.. Pollack et al. 2000 Prins et al. 2001), typically involve thin films (e.g., Gallardo et al. 1999) (e.g., Kataoka and Troian 1999), photoresponsive materials... 

Another typical photoresponsive material for preparation of switchable surfaces is the spiropyran-merocyanine system. The spiropyran isomerizes to zwitterionic merocyanine conformation by UV exposure, and the reverse reaction can be triggered by irradiation with visible light as well as azobenzene. The changes in hydrophilic/hydrophobic properties through the isomerization of spiropyran groups also enable the control of cell adhesion/ detachment. Edahiro et al. reported photoresponsive cell culture substrates grafted... 

In this section, we have examined several examples of dithienylethene derivatives that are suitable for dispersing in polymer matrices and processing into thin Aims. Although this approach to solid-state photoresponsive materials is convenient, it is limited by the amount of compound that can be incorporated into the matrix before segregaAon occurs. In Aie next secAon, we will explore how this limitaAon can be circumvented by integraAng Aie compounds directly into the polymer structure to produce high-content solid-state materials [65]. 

By now it should be obvious that there is considerable on-going effort to translate photoactive dithienylethene molecules into photoresponsive materials for use in numerous optoelectronic application areas. It should also be evident that despite its being advertised as one of the more versatile photoresponsive backbones, the hexatriene found in dithienylethene derivatives is plagued by some limitations. In this last section, we will explore how several groups are overcoming these problems by developing novel hexatriene systems that are based on the dithienylethene core stracture. In general, this is an exploratory science and many of the modifications lead to further problems. However, others open up the possibilities to new properties and applications. 

All the photoresponsive materials described above are based on covalent structures. However, the principles of supramolecular chemistry can be successfully applied to the design of non-covalent functional materials (de Greef et al, 2008,2009 Yagai and Kitamura, 2008). A clear advantage of supramolecular smart polymers stems from their easy preparation when compared with their covalent counterparts. In the case of supramolecular azopolymers, their preparation usually implies linking of the photochro-mic moieties to the macromolecular structure by means of non-covalent bonding. 

Oxacarixarenes (12) and (13) hearing azohenzene units were investigated (Scheme 6). Polyionic azacrown derivatives (14) containing azobenzene units were prepared and examined as photoresponsive materials. ... 

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