Light-Triggered Switchable Ionic Liquid Aqueous Two-Phase Systems

Abstract

Aqueous two-phase systems (ATPSs) consist of two immiscible aqueous phases where the mole fraction of water in both upper and bottom phases is higher than 0.8. ATPS has been widely used in many different fields since its discovery in 1896. However, easy control of phase transition is highly desired in many cases, which is still a challenge. Herein, we report the first work for the reversible switching of transition between two-phase ATPSs and single phase solution by light irradiation. It was found that azobenzene-based ionic liquids and inorganic salts in water systems could be reversibly switched between two-phase ATPS and homogeneous solution at ambient conditions by alternatively UV and visible light irradiation.Mechanism studies reveal that cationic isomerization of the azobenzene-based ionic liquids and size change of their micelles by UV and visible light irradiation is the main driving force for such reversible phase transition of ATPSs. This unique phase behavior has bridged the gap between ATPSs and chemical reactions, which is useful to create new chemistry in ATPSs. As an example of applications, highly efficient and selective aza-Michael reactions were performed in this novel kind of switchable ATPSs, which was well integrated with heterogeneous product 2 separation, and the phase components could be easily reused. This work opens a new way to conduct reactions efficiently with easy separation process.

A visible light/heat responsive covalent organic framework for highly efficient and switchable proton conductivity

“… 23 Significantly, light signal can be controlled remotely and precisely in space and time and switched rapidly in a clean and noninvasive way. 24 For the fabrication of light-responsive porous materials, an attractive strategy is to incorporate photo-switchable molecules, including azobenzene, spiropyran and diarylethene, 25 into the modular framework structures. Recently, a new kind of light/heat switchable molecules, donor–acceptor Stenhouse adduct (DASA), has been reported, which is capable of a reversible switching between the open neutral state (DASA-O) and closed zwitterionic state (DASA-C) triggered by visible light irradiation and heating in non-polar aromatic solvents.…”

Stimuli‐Responsive Ionic Liquids and the Regulation of Aggregation Structure and Phase Behavior†

“…In addition, the research group also developed light‐responsive aqueous two‐phase systems using the light‐responsive ILs. [ 81 ]…”

“…1) As catalysts or entrainment agents, stimuli‐responsive ILs have played an essential role in catalytic reactions, due to both their high catalytic activity in homogeneous catalysts and easy separation and recovery of heterogeneous catalysts. The main methods reported for stimuli‐responsive ILs in catalytic and separation are CO 2 , [ 42 ] magnetic, [ 135 ] light, [ 81 ] and temperature, [ 122,136‐143 ] which are supported by the phase behavior of emulsion, phase transfer, liquid‐liquid phase transition or CST phase behavior in the reactions of esterification, cycloaddition, hydrolysis, nitration, and hydroformylation. For example, Wang et al .…”

Highly Dispersed Ionic Liquids in Mesoporous Molecular Sieves Enable a Record NH3 Absorption

“…In the last two decades, ionic liquids (ILs) have been widely used in a variety of chemical processes, such as chemical reactions, − extraction and separation, − material preparation, − energy production, − and gas capture, − owing to their tunable physical and chemical properties with a judicious design of cation and anion structures. − The structural diversity of ILs brings great opportunities for tuning NH 3 –IL interactions and thus for designing high-efficient adsorbents for NH 3 capture. − Nevertheless, the absorption capacity of most “bulk” ILs is not high due to the less exposure of their active sites. Meanwhile, the high viscosity is another problem to impede their industrial applications …”