Synthesis and Properties of Quinoidal Fluorenofluorenes.

The synthesis and optoelectronic properties of 24 π-electron, formally antiaromatic fluoreno[3,2-b]fluorene and fluoreno[4,3-c]fluorene (FF), are presented. The solid-state structure of [4,3-c]FF along with computationally analogous molecules shows that the outer rings are aromatic while the central four rings possess a bond-localized 2,6-naphthoquinodimethane motif. The antiaromaticity and biradical character of the FFs is assessed computationally, the results of which indicate the dominance of the closed-shell ground state for these molecules.