To investigate the relationship between the optical properties and the phase separation of PPCx in solid states, we prepared thin films by drop-casting polymer solution (1 mg/mL in tetrahydrofuran) on glass substrates, followed by drying of the films under ambient condition. First, J-band was observed in the absorption spectra of PPC15 film. At 70 o C, J-band disappeared completely (Figure ). Subsequent cooling down to 25 o C enabled recovery of the J-band. The IVIS images of PPC15 films showed the highest FL intensity at 820 nm (Figure ). At 70 o C, the strongest FL was observed at 780 nm. With temperature decreased to 25 o C, the maximal FL intensity was observed at 820 nm again (Figure ).