To characterize the thermoresponsive properties of the NPs as described above, we first applied thermal treatment to PPC15 NPs which were heated from 25 o C. Upon heating, the intensity of the Jabsorption band at 789 nm decreased until disappearance at 55 o C, accompanied by the enhanced absorbance of the M-band at 740 nm (Figure ). After cooling down and maintaining at 25 o C for 30 min, the J-absorption band was recovered nearly completely (Figure ). The continuous attenuation of J-band with gradual increase of temperature (Figure & 4h) can be attributed to the heatinginduced decrease of Flory-Huggins interaction parameter χ, i.e. the incompatibility between PCL and chromophore. In addition, the increased vibrational and/or translational mobility of both fluorophores and polymers upon heating may also facilitate the dissociation of J-aggregates and even order-to-disorder transition within NPs. We further measured the absorption spectra over 5 heating-cooling cycles and found similarly periodic variations of the absorbance at 677, 740 and 789 nm, respectively, indicating the good reversibility of J-to-M transition (Figure ).