Intramolecular Charge Transfer in Antiaromatic Donor/Acceptor-Fused s-Indacenes

Herein we report the synthesis and characterization of four donor/acceptor-fused s-indacenes via the late-stage oxidation of a family of unsymmetrical benzofuran/benzothiophene-s-indacene regioisomers. A thorough study of their properties through experimental and computational analysis has revealed the effect of asymmetry on the molecular properties associated with antiaromaticity, as well as a strong correlation between antiaromaticity and intramolecular charge transfer (ICT). The strength of the charge transfer depends on the fusion orientation of the donor and acceptor motifs relative to the s-indacene core. The two most antiaromatic oxidized isomers exhibit strong evidence of ICT with 30 and 40 nm solvatochromic shifts.