Amplified Circularly Polarized Electroluminescence Behavior Triggered by Helical Nanofibers from Chiral Co-assembly Polymers

Two chiral binaphthyl polymers (R/S-P1 and R/S-P2) with different dihedral angles of the binaphthyl moiety were chosen as chiral inducers to construct chiral co-assemblies with an achiral pyrene-naphthalimide dye (NPy) and then acted as the emitting layer (EML) of circularly polarized electroluminescence (CP-EL) devices. The anchored dihedral angle of R/S-P2 not only exhibited the enhanced chirality signal, but also had a strong chirality-inducing effect on the achiral NPy dye in the chiral co-assembly (R/S-P2)(0.6)-(NPy)(0.4). After annealing at 120 degrees C, the CPL signal (|g(em)|) of ordered helical nano-fibers (R/S-P2)(0.6)-(NPy)(0.4) was amplified to 5.6x10(-2), which was about 6-fold larger than that of (R/S-P1)(0.6)-(NPy)(0.4). The amplified g(em) value of (R/S-P2)(0.6)-(NPy)(0.4) was due to the formation of a helical co-assembly through the strong pi-pi stacking interaction between the R/S-P2 and the achiral NPy. This kind of ordered helical nano-fibers (R/S-P2)(0.6)-(NPy)(0.4) acted as the EML of CP-OLEDs, and achieved an excellent CP-EL performance (|g(EL)|=4.8x10(-2)).