Substituent-induced modulation of proaromaticity in benzo-fused fluorenophenalene exhibiting 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 varied electronic character as apical substituent 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 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.