Tuning chromaticity based on energy transfer from the conjugated polymer to the Eu(TTA)3 moiety

The conjugated polymer P-1 was synthesized by the polymerization of 5,5'-divinyl-2,2'-bipyridine (M-1) and N,N'-bis(octyl)-1,7-dibromoperylene diimide (M-2) via Heck cross coupling. The bipyridyl moiety in P-1 can further incorporate Eu(TTA)(3)center dot 2H(2)O/Gd(TTA)(3)center dot 2H(2)O to generate polymer complexes P-2 and P-3, respectively. Interestingly, P-2 exhibits exceptional emissive properties which can be tuned by excitation wavelengths. For example, a green fluorescence can be obtained when P-2 is excited at 440 nm, whereas a red emission with a huge Stokes shift of 248 nm is observed when it is excited at 365 nm. The red fluorescence can be attributed to Eu(III) (D-5(0)-> F-7(2)), which is caused by an effective photoinduced energy transfer process between P-1 and the Eu(TTA)(3) moiety. However, P-3 only emits green fluorescence, and emission intensities depend on the selected excitation wavelengths. The rare excitation induced emission color change of P-2 has led to a better understanding the correlation of photophysical properties between perylenyl moiety and Eu(TTA)(3) moiety.