Characterization of the unusual metal-free, zinc, chloroindium, and ferrocenylindium 5,10,15,20-tetraferrocenylporphyrin anion-radicals by spectroelectrochemical, DFT, and TDDFT approaches

Anion-radicals of general formula [MTFcP]^- (M = 2H, Zn, InCl, and InFc; TFcP^2- is a dianion of 5,10,15,20-tetraferrocenylporphyrin) were prepared for the first time in situ by controlled potential reduction of the respective neutral MTFcP complexes in a thin layer spectroelectrochemical cell. UV-vis spectroscopy reveals the formation of a broad NIR band between 827-890 nm and another broad band in the Soret region between 458 and 527 nm. A similar NIR band has previously been assigned to 5,10,15,20-tetra(aryl)porphyrin radical-anions. Additional information on the electronic structure and nature of the vertical excitation energies in the [H₂TFcP]^- system were obtained by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. DFT calculations predict that the SOMO in the [H ₂TFcP]^- anion-radical is predominantly localized over the porphyrin core. TDDFT calculations suggest numerous MLCT transitions in addition to the expected π-π* excitations, which play a key role in the formation of unusual UV-vis spectra in the [MTFcP]^- anion-radicals.