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

Poly-(ionicliquid)-s (PILs) have been widely applied invariousdisciplines because of their unique physical, chemical, and electricalcharacteristics. To broaden the applications of PILs, stimuli-responsivePILs based on different stimuli have been investigated. Special stimuli-dependentproperties of PILs, especially photo-regulated electrical conductivities,however, have not yet been fully accomplished. In this work, we studythe photo-regulated electrical conductivities of PIL films by using[C(3)mim-MA]-[TFSI], azobisisobutyronitrile, and poly-(ethyleneglycol) dimethacrylate as an ionic liquid monomer, an initiator, anda crosslinker, respectively. Spiropyran (SP) molecules, which canconvert to merocyanine molecules under UV light irradiation, are usedas photo-responsive agents. As a result, stretchable and photo-responsiveconductive PIL-SP films can be fabricated, which can be reversiblyconverted to PIL-merocyanine films under UV and visible light illuminations.The photoluminescence properties are confirmed by fluorescence andUV-vis spectra. Furthermore, the reversible photo-regulatedelectrical properties are investigated by shining UV and visible lights,presented by the Bode plots and Nyquist plots. The PIL-SP films withdifferent crosslinker ratios (1, 5, and 10x) all exhibit similarphoto-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 filmsexpands the applications of PIL materials.