Optically active cyclic compounds based on planar chiral [2.2]paracyclophane: extension of the conjugated systems and chiroptical properties

Abstract

A series of optically active cyclic compounds based on the planar chiral tetrasubstituted [2.2]paracyclophane core were synthesized to obtain luminescent materials with excellent chiroptical properties in both the ground and excited states. The optical resolution of tetrasubstituted [2.2]paracyclophane was carried out using our previously reported method. The obtained cyclic compounds were composed of the optically active propeller-shaped structures created by the [2.2]paracyclophane core with p-phenylene–ethynylene moieties. The compounds exhibited good optical profiles, with a large molar extinction coefficient (ε) and photoluminescence quantum efficiency (Φ_lum). The emission occurred mainly from the propeller-shaped cyclic structures. This optically active higher-ordered structure provided chiroptical properties of high performance, such as a large specific rotation ([α]_D) and molar ellipticity ([θ]) in the ground state and intense circularly polarized luminescence (CPL) with large dissymmetry factors (g_lum) in the excited state. The results suggest that planar chiral [2.2]paracyclophane-based optically active higher-ordered structures, such as the propeller-shaped cyclic structure, are promising scaffolds for obtaining CPL and that appropriate modifications can enhance the CPL characteristics.