Synthesis and Characterization of a Cyclic Trimer of a Chiral Spirosilabifluorene

Abstract

A chiral shape‐persistent macrocyclic compound (Si‐[3]), designed by the C/Si substitution in the spiro‐atom of spirobifluorene in the cyclic trimer (C‐[3]), has been successfully synthesized in this study. The C/Si substitution made the spiro‐conjugation and energy levels of HOMO and LUMO decrease. Due to the silicon substitution, the macrocyclic compound Si‐[3] was able to be degraded by fluoride ions, but its reaction rate was slower than that of the unsubstituted spirosilabifluorene, showing the chemical stability of Si‐[3]. Furthermore, the chiroptical properties of Si‐[3] with D3‐symmetric macrocyclic structure were investigated, and (M,M,M)‐Si‐[3] showed high emission quantum yield (Φf = 80%) and moderate dissymmetry factor of circularly polarized luminescence (CPL) (glum,exp = −1.2 × 10−3). According to the the time‐dependent density‐functional theory (TD‐DFT) calculations using polarizable continuum model (PCM), the bright CPL from Si‐[3] was explained by a planarization of one bisilafluorenyl moiety at the excited state, which is responsible for the almost fully‐allowed radiative transition with a short emission lifetime of tf = 1.89 ns.