Tuning Electron-Transfer Properties in 5,10,15,20-Tetra(1′-hexanoylferrocenyl)porphyrins as Prospective Systems for Quantum Cellular Automata and Platforms for Four-Bit Information Storage

Metal-free (1) and zinc (2) 5,10,15,20-tetra(1'-hexanoylferrocenyl)porphyrins were prepared using an acid catalyzed tetramerization reaction between pyrrole and 1'-(1-hexanoyl)ferrocencarboxaldehyde. New organometallic compounds were characterized by combination of H-1, C-13, and variable-temperature NMR, UV-vis, magnetic circular dichro- ism, and high-resolution electrospray ionization mass spectrometry methods. The redox properties of 1 and 2 were probed by electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation approaches coupled with UV-vis-near-IR and Mossbauer spectroscopy. Electrochemical data recorded in the dichloromethane/TBA[B(C6F5)(4)] system (TBA[B(C6F5)(4)] is a weakly coordinating tetrabutylammonium tetrakis(pentafluorophenyl)borate electrolyte) are suggestive of "le(-) + le(-) + 2(e-") oxidation sequence for four ferrocene groups in 1 and 2, which followed by oxidation process centered at the porphyrin core. The separation between all ferrocene-centered oxidation electrochemical waves is very large (510-660 mV). The nature of mixed-valence [1](n+) and [2](n+) (n = 1 or 2) complexes was probed by the spectroelectrochemical and chemical oxidation methods. Analysis of the intervalence charge-transfer band in [1]+ and [2] is suggestive of the Class II (in Robin-Day classification) behavior of all mixed-valence species, which correlate well with Mossbauer data. Density functional theory polarized continuum model (DFT-PCM) and time-dependent (TD) DFT-PCM methods were applied to correlate redox and optical properties of organometallic complexes 1 and 2 with their electronic structures.