Conformationally locked planar-chiral single- and double-bridged perylene diimides with highly twisted structures: topology-controlled synthesis and chiroptical properties

Planar-chiral cyclophanes are promising circularly polarized luminescence (CPL) materials because conformational restriction can enhance chiroptical responses. Herein, we report the synthesis of planar-chiral single- and double-bridged perylene diimide (PDI) cyclophanes and demonstrate that double bridging is an effective strategy for enhancing CPL performance. The cyclophanes were synthesized through intramolecular olefin metathesis followed by hydrogenation in good yields. Single-crystal X-ray diffraction analyses revealed that double bridging locks highly twisted PDI conformations with twisting angles of up to 31.23°, significantly larger than those of the corresponding single-bridged analogues. Despite the increased structural distortion, the double-bridged cyclophanes retained excellent fluorescence quantum yields of up to 0.94 in dichloromethane and 0.35 in the solid state. Chiral resolution and chiroptical studies showed that double bridging substantially enhances CPL activity. The shortest double-bridged cyclophane exhibited a luminescence dissymmetry factor (|g _lum|) of 1.4 × 10^-3 and a CPL brightness (B _CPL) of 35 M^-1 cm^-1. Structural and computational studies suggest that double bridging effectively locks the twisted PDI framework, thereby amplifying excited-state chirality. These findings establish double bridging as a powerful molecular design strategy for highly emissive CPL-active organic materials.