Bismetal Complexes of 5,20-Bis(5-formyl-2-pyrrolyl)-[26]hexaphyrin(1.1.1.1.1.1) Exhibiting Strong Near-Infrared Region Absorptions

[26]Hexaphyrin(1.1.1.1.1.1) bearing two 5-formyl-2-pyrrolyl groups at the 5- and 20-positions was prepared by cross-condensation of 5,10-bis(pentafluorophenyl)-substituted tripyrrane with 2,5-diformylpyrrole as an effective binuclear metal-coordinating ligand, owing to the two hemiporphyrin-like NNNN pockets. In fact, metalation of this hexaphyrin with Zn-II, Cu-II, and Pd-II salts proceed smoothly at room temperature to give the corresponding bismetal complexes that displayed remarkably redshifted absorption spectra reaching deep into near infrared region. These redshifted absorption bands are ascribed, through electrochemical investigations and DFT calculations, to two structural motifs: the N-metalopyrrole substructure that elevates the HOMO level due to the electron-donating property and the two coordinated metal ions that serve as Lewis acids to lower the LUMO level.