As seen in Fig. 2, the probe shows

As seen in Fig. 2, the probe shows quite different fluorescence emission behaviors in the anionic surfactant micelle than in the other three micelles. In the anionic SDS micelles, the dual-fluorophore shows not only the monomer emission of pyrene at 380 and 400 nm, but also comparatively intensive rhodamine emission at 580 nm, suggesting the rhodamine unit adopts a ring-opening form of the spirolactam unit in SDS micelles [23]. However, in all the other three types of micelles, the probe shows only strong pyrene monomer emission but not apparent rhodamine emission, indicating the rhodamine part is still in the form of spirolactam with close-ring structure. Similar phenomena were also observed for the absorption behaviors of the probe in these surfactant micelles. As illustrated in Fig. S8 (ESI), the probe exhibits rhodamine absorption bands over 500~600 nm only in SDS micelles. The absence of both absorption and emission of rhodamine unit in other three types surfactant micelles suggest that the ring-open process of the spirolactam unit is selective to anionic SDS micelles. Moreover, a comparatively larger intensity ratio of rhodamine emission to pyrene monomer is observed in SDS micelles, and the solution color is quite different for the dual-chromophore in the four micelle solutions (see inset of Fig. 2), which makes the probe capable of selectively recognizing anionic surfactant over other types of surfactants.