Thermally Reversible On‐Off Switching of Aggregation‐Induced Emission via LCST Phase Transition of Ionic Liquids in Water

Abstract

A new phosphonium‐based ionic liquid is designed and synthesized using the 1,1,2,2‐tetraphenylethene‐derived anion ([P4444]4[TSPE]). Aqueous solutions of [P4444]4[TSPE] are obtained as transparent liquids (monophasic state), which suspended with increasing temperature. This behavior is found to exhibit a lower critical solution temperature (LCST) phase transition behavior. The LCST phase transition temperature can be controlled from 36 to 55 °C by changing the weight ratio between [P4444]4[TSPE] and water. When observing the LCST phase transition behavior of aqueous solutions of [P4444]4[TSPE] under excitation light with a wavelength of 365 nm, negligible photoluminescence in the monophasic state is observed at room temperature. Conversely, strong photoluminescence is observed in the suspended state when the temperature is above the LCST phase transition temperature. This strong photoluminescence is attributed to aggregation‐induced emission (AIE) that is induced by the restriction of the intramolecular rotations of the 4‐sulfophenyl groups against the ethylene core in the [TSPE] anion. This behavior is thermally reversible. This is the first example of on‐off switching of AIE achieved using the LCST behavior of ionic liquids.

AIEgen-incorporated nanoparticles as a probe for the construction of dual-luminophore pressure- and temperature-sensitive coatings

“…It is known that the luminescence of AIEgens may be influenced by temperature, [44][45][46][47] which has been exploited in the measurement of the glass transition temperature 48,49 and the upper or lower critical solution temperature of polymers. [50][51][52] Previously, we embedded an AIEgen, i.e., tetra(4-nitrophenyl) ethylene (TPE-4N), into silicone, and found that its photoluminescence intensity is sensitive to the environmental temperature. 43 Although the characteristic is promising for the fabrication of dual temperature-and pressure-sensitive coatings, two issues need to be solved.…”

A processable ionogel with thermo-switchable conductivity

“…9 The responsiveness of these ionogels is generally derived from the combined effects of responsive polymers, ionic liquids (ILs), or the compatibility between these components. 10–15 For example, mechano-responsive ionogels with tunable color and shape have been prepared by incorporating spiropyran-based polymers into the gel matrix. 16,17 By virtue of the design ability of ILs, a variety of stimuli-responsive ILs have been synthesized, providing a versatile platform for creating smart ionogels with reversible color change.…”