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When upconversion nanophosphors were incorporated into an azotolane-containing cross-linked liquid-crystal polymer film, the resulting composite film generated fast bending upon exposure to continuous-wave near-IR light at 980 nm. This occurs because the upconversion luminescence of the nanophosphors leads to trans-cis photoisomerization of the azotolane units and an alignment change of the mesogens. The bent film completely reverted to the initial flat state after the light source was removed.
Wu et al. (Tue,) studied this question.