Electron-Transfer Processes in Metal-Free Tetraferrocenylporphyrin. Understanding Internal Interactions To Access Mixed-Valence States Potentially Useful for Quantum Cellular Automata

Redox properties of H(2)TFcP TFcP(2-) = 5,10,15,20-tetraferrocenylporphyrin(2-) were investigated using cyclic voltammetry, differential pulse voltammetry, and square-wave voltammetry methods in a large variety of solvents and electrolytes. When DMF, THF, and MeCN were used with TBAP as the supporting electrolyte, the first oxidation wave was assigned to a single four-electron oxidation process reflecting simultaneous oxidation of all iron(II) centers into iron(III) centers in H(2)TFcP. When an o-DCB (1,2-dichlorobenzene)/TBAP combination was used in electrochemical experiments, four ferrocene substituents underwent two very diffuse, "two-electron" stepwise oxidations. The use of a weakly coordinating TFAB (NBu(4)B(C(6)F(5))(4)) electrolyte in o-DCB or DCM results in four single-electron oxidation processes for ferrocene substituents in which the first and second single-electron waves have a relatively large separation, while the second, third, and fourth oxidation processes are more closely spaced; similar results were observed when a DCM/TBAP system and an imidazolium cation-based ionic liquid ((bmim)Tf(2)N = N-butyl-N'-methylimidazolium bis(trifluoromethanesulfonyl)imide) were used. Spectroelectrochemical oxidation of H(2)TFcP in o-DCB or DCM with TFAB as the supporting electrolyte allowed for characterization of the mixed-valence H(2)TFcP(+), H(2)TFcP(2+), and H(2)TFcP(3+) compounds by UV-vis spectroscopy in addition to the "all-Fe(III)" H(2)TFcP(4+). The chemical oxidation of H(2)TFcP was tested using a variety of oxidants which resulted in formation of mixed-valence H(2)TFcP(+) and H(2)TFcP(2+) as well as H(2)TFcP(4+), which were characterized by UV-vis-NIR, MCD, IR, Mossbauer, and XPS spectroscopy. The intervalence-charge-transfer bands observed in the near-IR region in H(2)TFcP(+) and H(2)TFcP(2+) complexes were analyzed using Hush formalism and found to be of class II (in Robin-Day classification) character with localized ferrous and ferric centers. Class II behavior of H(2)TFcP(+) and H(2)TFcP(2+) complexes was further confirmed by Mossbauer, IR, and XPS data.