Topoisomers and aromaticity of a redox active 50π core-modified isophlorinoid.

A 50π decathiophene expanded isophlorin adopts a unique [6+4] conformation and a near-planar conformation depending on the solvent of crystallization and undergoes a reversible two electron oxidation to yield the largest planar antiaromatic dication bearing 48π-electrons. Cyclic voltammetry studies revealed the redox active nature of this macrocycle with multiple oxidation and reduction potentials. Spectro-electrochemical measurements confirmed a facile reversible two-electron oxidation and the unstable radical cation intermediate in these systems. Quantum chemical calculations that were employed to estimate NICS(0) values revealed a weak diatropic ring current for the 50π macrocycle and an intense paratropic ring current for the 48π dicationic species.