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

Abstract

Pyrene-based chiral ligands (LR and LS) consisting of two chiral imidazole sidearms at the 1,8-positions first form pyrene-bridged oligomers [(L(R or S))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(R or S))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 (|gCD| = 0.006) and circularly polarized luminescence (|gCPL| = 0.01).