Photochromic Room Temperature Ionic Liquids Based on Anionic Diarylethene Derivatives

Two photochromic room-temperature ionic liquids (RTILs) based on anionic diarylethene derivative (DTE) were synthesized and characterized. Photochemical (quantum yields for ring closure and opening) and electrochemical (cyclic voltammetry) properties of the [ALIQUAT](2)[DTE] and [P-6,P-6,P-6,P-14](2)[DTE] compounds as amorphous salts have been investigated. All compounds (including the di-acid precursor and two RTILs) were studied in solution, in their intrinsically pure forms (RTIL as unique media) and in the solid state (BaSO4 support). Combination with larger organic cations can stabilize the closed-ring form, apparently avoiding the formation of by-products without photodegradation. It is observed that the closed-ring reaction is faster in the case of RTILs comparing to the di-acid starting material. The coloration switches between transparent (initial state) to purple ([ALIQUAT](2)[DTE]) or pink ([P-6,P-6,P-6,P-14](2)[DTE]). The novel diarylethene-based RTILs as multi-coloured photochromic materials can open attractive perspectives for materials science applications.