Off-off-on chiroptical property switching of a pyrene luminophore by stepwise helicate formation

Pyrene-based chiral ligands (L-R and L-S) consisting of two chiral imidazole sidearms at the 1,8-positions first form pyrene-bridged oligomers [(L-(RorS))(3)(Zn2+)(n)], which are chiroptically inactive, with a low concentration of zinc ions (Zn2+). Upon addition of more Zn2+, chiroptically active coordination helicates ([(L-(RorS))(3)(Zn2+)(2)]) are formed. The stepwise assembly process successfully facilitated an off-off-on chiroptical switching process of a pyrene luminophore controlled by the concentration of Zn2+. The resulting pyrene-bridged helicates exhibit high performance in terms of a dissymmetry factor of circular dichroism (|g(CD)| = 0.006) and circularly polarized luminescence (|g(CPL)| = 0.01).