Substituent-induced modulation of proaromaticity in benzo-fused fluorenophenalene exhibiting a low-lying LUMO

Abstract

Fluorenophenalene (FP) is an underexplored proaromatic polycyclic hydrocarbon. Herein, we report the synthesis of benzo-fused FPs bearing aryls (mesityl, C₆H₂F₃ and C₆F₅) of varying electronic character as apical substituents of the cyclopenta-unit with large HOMO/LUMO coefficients. Benzo-fusion expands the p-quinoidal conjugation length by forming a polyene-like subunit, while electron-deficient aryls improve the electronic communication. As a result, the HOMO–LUMO gap decreases as the core aromaticity increases. Replacing a mesityl pendant with C₆H₂F₃ and C₆F₅ lowers the LUMO energy, steadily stabilizing it from −3.08 eV to −3.64 eV and −4.20 eV, respectively, highlighting our design efficacy.