Peripheral Fabrications of a Bis-Gold(III) Complex of [26]Hexaphyrin(1.1.1.1.1.1) and Aromatic versus Antiaromatic Effect on Two-Photon Absorption Cross Section

Peripheral modifications of bis-gold(III) [26]hexaphyrin(1.1.1.1.1.1) have been explored via perbromination and subsequent Pd-catalyzed cross-coupling reactions. β-Phenylethynylated [26]hexaphyrin complex shows the large two-photon absorption (TPA) value due to its extended π-conjugation. Aromatic-to-antiaromatic switches through two-electron reduction from [26]hexaphyrins to [28]hexaphyrins cause a sharp drop in TPA value, which has emerged as a new quantitative measure of aromaticity versus antiaromaticity.