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

Abstract

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)₃·2H₂O/Gd(TTA)₃·2H₂O 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) (⁵D₀ → ⁷F₂), 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.