As shown in Figure , upon exposure to UV light, the original peak of red emission at ~620 nm gradually decreased, while the peak at ~480 nm increased dramatically. Eventually, after 20 min, a single blue emission peak was obtained. As a result, a visible emission color change could be observed with the naked eye (Figures 6B and , and the supplementary video). This photochromic fluorescence response was also observed in the polymer aggregates in DMF/H2O (5/95, v/v) (Figure top, Figure ).