Solvent-sensitive circularly polarized luminescent compounds bearing a 9,9'-spirobi[fluorene] skeleton

A series of chiral 9,9'-spirobi[fluorene] (SBF) derivatives with diphenylamino donor and cyano acceptor units were designed as a new family of circularly polarized luminescent materials. The designed SBF derivatives were successfully synthesized from 7,7'-dibromo-9,9'-spirobi[fluorene]-2,2'-diol. No racemization occurred in the synthetic sequence. Therefore, each enantiomer of the SBF derivatives can be prepared from the enantiomerically pure starting material. Absorption and fluorescence spectroscopy and theoretical calculations revealed that the phenylene linker between the donor/acceptor units and the SBF core has a great impact on their photophysical properties. In particular, the phenylene linker was found to induce a red shift in their emission bands. The obtained chiral SBF derivatives exhibited solvent-dependent circularly polarized luminescence owing to their donor-π-acceptor structures.