Photomechanical response

Seki, T., Tanaka, K., and Ichimura, K. Photomechanical Response in Monolayered Polymer Films on Mica at High Humidity. Macromolecules 30, 6401 (1997). 

Depending on the lateral-packing density, the monolayers showed photo-driven large and characteristic 2D and 3D morphological changes at a submicrometer scale. This might be the first visualization of the photomechanical response of a monolayered photochromic polymer taking place on a solid surface. ... 

Surface-relief grating (SRG, regular topological surface modification) formed via irradiation with an interference pattern of coherent light has been demonstrated only recently/ " and is perhaps the most attractive target in the current research of azo polymers (Chapters 13 and 14 of this book focus on this subject). It is still unclear whether there are any common mechanisms involved between SRG formation and the photomechanical response observed in monolayers described in Section 15.4.1. Nevertheless, with regard to photoinduced motions in Az polymers, it is quite important to proceed with SRG experiments. 

Seki T, Fukuda R, Yokoi M, Tamaki T, Ichimura K. 1996. Photomechanical response of azobenzene containing monolayers on water surface. Bull Chem Soc Jpn 69 2375 2381. 

Figure 3.29. (a) Photomechanical response of an LCE sample, (b) The shape deformation of an LCE sample upon exposure to light at A = 514 nm. (c) Mechanism of the locomotion of the dye-doped LCE sample. Source Camacho-Lopez et al., 2004. 

Photomechanical Responses of Azobenzene-Containing Materials. Ji et al. (2004) reported that a self-assembled monolayer (SAM) of azobenzene molecules on a silicon microcantilever created a photon-driven switch. Commercial silicon microcantilevers were electron-beam coated on one side with 3nm of primer layer (chromium), followed by 20 nm of gold. An azobenzene derivative with a decanthiol substituent on one ring was used to functionalize the gold surface. The thiol (-SH) end attached to the gold surface and the other azobenzene end disposed outward. 

Other than the SAMs and azobenzene-containing organic polymers, azobenzene-modified hybrid polysilsesquioxane gels were also studied for their photomechanical responses. 

As a control, polyurethane-acrylate copolymers without photo-chromic agents were subjected to the same photo-mechanical test. No significant photomechanical response was observed. 

There are two postulated mechanisms for photomechanical response, which taken together can explain the photochromic effect seen in this work. The first by Lovrien, " suggest that if a polymer interacts with some photochromic chromophore, it may undergo a conformational change when irradiated because the interactions between the polymer and the chromophore suffer changes. The second one, postulated by Matejka" and Irie, suggest that... 

Kim T, Zhu L, Mueller LJ, Bardeen CJ (2012) Dependence of the solid-state photomechanical response of 4-chlorocinnamic acid on crystal shape and size. Cryst Eng Commun 14 7792-7799... 

In crosslinked liquid-crystalline polymers and elastomers, and more recently also in azobenzene crystals, photoisomerization can lead to reversible macroscopic shape changes and complex 3D movements [34] as illustrated in Fig. le. The key for achieving large-scale photomechanical response is an efficient control over molecular alignment and, as mentioned earlier, liquid-crystalline materials are particularly useful in this respect. The optical-to-mechanical energy conversion provides a pathway to the use of light to fuel photomechanical oscillators [35], plastic micromotors [36], robotic-arm movements [37], etc. 

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