Switching Light Transmittance by Responsive Organometallic Poly(ionic liquid)s: Control by Cross Talk of Thermal and Redox Stimuli

A novel organometallic poly(ionic liquid) with both redox- and thermoresponsive properties is synthesized from a poly(ferrocenylsilane) (PFS) via a one-step Strecker sulfite alkylation reaction by using tetraalkylphosphonium sulfite as an effective and versatile nucleophile. This dual-responsive polymer is composed of a PFS backbone and quaternary phosphonium sulfonate side groups and exhibits a concentration-dependent lower critical solution temperature (LCST)-type phase transition in aqueous solution. Furthermore, the LCST-type phase behavior of the polymer can be switched between the “off” state and “on” state by chemical or electrochemical oxidation and reduction on the ferrocene units in the polymer main chain. As a consequence, a classical LCST-type phase transition, as well as an “isothermal” redox-triggered phase transition can be induced by using thermal and electrochemical triggers without changing the composition of the system. On the basis of this dual responsiveness, a “smart window” device is fabricated. The optical characteristics of this device are completely unaltered after 100 thermal and/or redox cycles.