Developing Stretchable and Photo-Responsive Conductive Films by Incorporation of Spiropyran into Poly(ionic liquid)s

Poly(ionic liquid)s (PILs) have been widely applied in various disciplines because of their unique physical, chemical, and electrical characteristics. To broaden the applications of PILs, stimuli-responsive PILs based on different stimuli have been investigated. Special stimuli-dependent properties of PILs, especially photo-regulated electrical conductivities, however, have not yet been fully accomplished. In this work, we study the photo-regulated electrical conductivities of PIL films by using [C3mim-MA][TFSI], azobisisobutyronitrile, and poly(ethylene glycol) dimethacrylate as an ionic liquid monomer, an initiator, and a crosslinker, respectively. Spiropyran (SP) molecules, which can convert to merocyanine molecules under UV light irradiation, are used as photo-responsive agents. As a result, stretchable and photo-responsive conductive PIL-SP films can be fabricated, which can be reversibly converted to PIL-merocyanine films under UV and visible light illuminations. The photoluminescence properties are confirmed by fluorescence and UV–vis spectra. Furthermore, the reversible photo-regulated electrical properties are investigated by shining UV and visible lights, presented by the Bode plots and Nyquist plots. The PIL-SP films with different crosslinker ratios (1, 5, and 10×) all exhibit similar photo-regulating electrical properties. At higher crosslinker ratios, the DC resistances are higher, resulting in lower conductivities. The study of stretchable and photo-responsive conductive PIL-SP films expands the applications of PIL materials.