Synthesis and Characterization of a Cyclic Trimer of a Chiral Spirosilabifluorene

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 D 3 ‐symmetric macrocyclic structure were investigated, and ( P , P , P )‐ Si‐[3] showed a high emission quantum yield ( Φ f =80 %) and moderate dissymmetry factor of circularly polarized luminescence (CPL) ( g lum,exp =−1.2×10 −3 ). According to 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 τ f =1.89 ns.