Endowing a Light-Inert Aqueous Surfactant Two-Phase System with Photoresponsiveness by Introducing a Trojan Horse.

The ability to modulate the phase behavior of an aqueous surfactant two-phase (ASTP) system reversibly with light is of great importance in both fundamental and applied science. Thus far, most of the light-responsive ASTP systems are based on covalent modification of the component molecules. In this article, we, for the first time, achieve photoresponsiveness in a light-inert ASTP system by physically introducing a phototrigger with the aid of a Trojan horse. The ASTP system formed from sodium laurate (SL) and dodecyltributylammonium bromide (DBAB) does not show light responsiveness by physically mixing a light-responsive azobenzene compound, 2-(4-(phenyldiazenyl)phenoxy)acetate sodium (Azo). However, in the presence of the host-guest complex SL@β-CD formed from β-CD and sodium laurate (SL), the ASTP turns quickly into a homogeneous suspension under visible light, which recovers to the original ASTP state again under 365 nm UV irradiation. Because the SL@β-CD complex exists harmonically with the ASTP system, it can be viewed as a "Trojan horse" that becomes fatal only when the encapsulated SL is triggered to release. In the presence of the Trojan horse, the photoresponsiveness of the ASTP system can be manipulated reversibly by alternatively exerting UV and visible light. Using this strategy, we are able to collect trace amounts of oily components from water. The current strategy points out that it is possible to achieve light responsiveness in light-inert systems with a physical method, which may have profound impact on both the fundamental and applied science.