Fluoreno[4,3-c]fluorene: a closed-shell, fully conjugated hydrocarbon.

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Antiaromaticity in π-conjugated systems presents unique electronic properties.
• Fluorene-based molecules are of interest for organic electronics.
• Understanding biradical character is crucial for predicting molecular stability and reactivity.

Purpose of the Study:

• To synthesize and characterize a novel 24 π-electron fluoreno[4,3-c]fluorene (FF) derivative.
• To investigate the solid-state structure and optoelectronic properties of FF.
• To determine the biradical character and ground state nature of FF.

Main Methods:

• Synthesis of 4,11-di-t-butyl-1,8-dimesitylfluoreno[4,3-c]fluorene.
• X-ray crystallography for solid-state structure determination.
• Experimental and computational methods to assess biradical character.

Main Results:

• The synthesis of the target fluoreno[4,3-c]fluorene molecule was successful.
• Solid-state structure revealed aromatic outer rings and a central naphthoquinone dimethide motif.
• Experimental and computational data indicate a closed-shell ground state, not a biradical.

Conclusions:

• The synthesized fluoreno[4,3-c]fluorene (FF) possesses a stable closed-shell ground state.
• The molecule's structure features a unique combination of aromatic and bond-localized motifs.
• This study provides insights into the electronic properties of formally antiaromatic π-conjugated systems.