Chiral blue box host-guest encapsulation induced CPL from achiral planar fluorescence dyes

Abstract

Chiral supramolecular hosts that induce circularly polarized luminescence (CPL) of encapsulated fluorescent dyes are considered an effective strategy for constructing CPL-active materials. Blue box, a tetracationic cyclophane featuring well-defined aromatic panels, exhibits a strong capability for binding planar aromatic guests. However, the construction of chiral blue boxes and their application in inducing guest CPL have not yet been reported. Herein, we report the synthesis of an intrinsically chiral blue box (Binbox) through the incorporation of an R-binaphthol unit. Single-crystal X-ray diffraction analysis, combined with chiroptical measurements, reveals that the introduction of the binaphthol moiety not only reduces the symmetry of the parent blue box from a highly symmetric structure to C 1 symmetry, but also imparts pronounced chiroptical activity, thereby enabling blue CPL emission with a luminescence dissymmetry factor (g lum ) of up to 4.0 × 10 -3 . More importantly, the chiral blue box exhibits strong host-guest binding ability toward selected planar cationic dyes. CD and CPL experiments demonstrate that guest encapsulation not only enables effective chirality transfer from host to guest, but also induces CPL emission of the guests in the 500-650 nm range, with g lum values in the range of 1.2 × 10 -3 to 4.3 × 10 -3 . These results demonstrate that host-guest chemistry of chiral blue box provides a convenient supramolecular strategy for the development of CPL-active materials.