S. Schultzke, Prof. A. Staubitz* University of Bremen *Prof. Anne Staubitz, Institute for Analytical and Organic Chemistry, University of Bremen, Leobener Straße 7, D-28359 Bremen, Germany For photo bending of LCEs the basic concept is the introduction of a liquid crystalline phase by using azobenzene derivatives as mesogens, which can be aligned by a variety of techniques and are typically fixed by polymerization. By using UV-light, azobenzenes can switch from the thermodynamically more stable, flat, extended E-form to the more helical, contracted Z-form. (Figure 1) One issue in the context of the interaction of these materials with living organisms is the fact that switching occurs with harmful UV-light. A further problem is that linearly polarized light (by which the bending direction can be modulated) is much more difficult to generate with UV light than it is with light in the visible range, where cheap filters exist that can be used in front of the light source. We synthesized a conceptually new photo mechanical LCE: It has been described that the ortho-functionalization of azobenzenes leads to switching in the visible region. (Figure 1) However, the four additional fluorine atoms destroying any liquid crystallinity. In the new molecule, liquid crystallinity is re-introduced. Therefore, the molecule is both liquid crystalline and switches with visible light; the photomechanical effect is brought about by a volume change and disturbance of the mesogens by switching. This geometric change on the molecular level then translates to a movement on the macroscopic scale (photomechanical effect, Figure 2).

Photomechanical bending of polymeric liquid crystalline elastomers (LCEs) with visible light

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