Then, the fluorescence emission spe

Then, the fluorescence emission spectra of PyERh in SDS aqueous solution were examined systematically by varying SDS concentration. As illustrated in Fig. 3a, the probe shows variable fluorescence emission in different SDS-concentrated solutions. When SDS concentration is smaller than 8 mM as in pre-micelle states, the probe exhibits multiple emission bands that contain pyrene monomer at 380 and 400 nm, pyrene excimer centering at 510 nm, and rhodamine emission centering at 580 nm. When SDS concentration is at or above 8 mM as in micellar states, the pyrene excimer emission rapidly reduces to very weak intensity accompanied with strongly enhanced pyrene monomer and rhodamine emission. The solution color changes from green gradually to yellow, orange and then to red along SDS concentration increases (inset of Fig. 3a). The intensity ratio of either monomer emission to excimer orrhodamine emission to excimer shows a sharp reduction at 7 mM SDS and becomes flattened at 8 mM SDS and above (Fig. 3b). The surface tension measurements showed that the CMC of SDS in the presence of 10 μM PyERh changes to 6.87 mM (Fig. S9, ESI). These results suggest the variation of SDS aggregation states can well modulate the fluorescence emission, and conversely, the latter can well probe the aggregation changes of SDS assemblies. Differently, the concentration variation of the other three types of surfactants could not induce rhodamine emission whether the concentration is smaller or above its CMC, although the pyrene emission is heavily modulated (Fig. S10, ESI). These results once again approve that the dual-fluorophore can be used to selectively recognize anionic surfactants over other three types of surfactants.