Tetraferrocenylporphyrins as active components of self-assembled monolayers on gold surface.

Novel tetraferrocenylporphyrins-containing self-assembled monolayers were prepared employing two different approaches. Self-assembled monolayers were characterized using UV-Vis spectroscopy and cyclic voltammetry (CV) whereas their photoelectrochemical properties were investigated by photocurrent generation (PG) experiments

Long-Range Electronic Communication in Free-Basemeso-Poly(Ferrocenyl)-Containing Porphyrins

H_2FcPh_3P [FcPh_3P = 5-ferrocenyl-10,15,20-triphenyl porphyrin(2-)], cis-H_2Fc_2Ph_2P [cis-Fc_2Ph_2P = 5,10-bisferrocenyl-15,20-diphenyl porphyrin(2-)], trans-H_2Fc_2Ph_2P [trans-Fc_2Ph_2P = 5,15-bisferrocenyl-10,20-diphenyl porphyrin(2-)], and H_2Fc_3PhP [Fc_3PhP = 5,10,15-trisferrocenyl-20-phenyl porphyrin(2-)] along with H_2TPP [TPP = 5,10,15,20-tetraphenylporphyrin] and H_2TFcP [TFcP = 5,10,15,20-tetraferrocenyl porphyrin(2-)] were isolated from the direct cross-condensation reaction between pyrrole, benzaldehyde, and ferrocene carboxaldehyde or from the reaction between ferrocenyl-2,2'-dipyrromethane and benzaldehyde, suggesting a scrambling reaction mechanism for the last approach. All compounds were characterized by UV-vis, MCD, and NMR spectroscopy; APCI MS and MS/MS methods; as well as high-resolution ESI MS spectrometry. The conformational flexibility of ferrocene substituents in all compounds was confirmed using variable-temperature NMR and computational methods. DFT calculations were employed to understand the degree of nonplanarity of the porphyrin core as well as the electronic structure of ferrocene-containing porphyrins. In all cases, a set of occupied, predominantly ferrocene-based molecular orbitals was found between the highest occupied and the lowest unoccupied, predominantly porphyrin-based molecular pi orbitals. The redox properties of all ferrocene-containing porphyrins were investigated in a CH_2Cl_2/TFAB [TFAB = tetrabutylammonium tetrakis(perfluorophenyl)borate] system using cyclic voltammetry, differential pulse voltammetry, and square wave voltammetry methods. In all cases, oxidations of individual ferrocene substituent(s) along with porphyrin core oxidation(s) and reductions have been observed. Mixed-valence [cis-H_2Fc_2Ph_2P]^+, [trans-H_2Fc_2Ph_2P]^+, [H_2Fc_3PhP]^+, and [H_2Fc_3PhP]^(2+) complexes were formed in situ under spectroelectrochemical and chemical oxidation conditions and were characterized using UV-vis and MCD approaches. Analysis of intervalence charge-transfer bands observed in the NIR region for all mixed-valence complexes suggests electron localization and thus class II behavior in the Robin-Day classification

Metal-free and transition-metal tetraferrocenylporphyrins part 1: synthesis, characterization, electronic structure, and conformational flexibility of neutral compounds

H(2)TFcP [TFcP = 5,10,15,20-tetraferrocenyl porphyrin(2-)] was prepared by a direct tetramerization reaction between pyrrole and ferrocene carbaldehyde in the presence of a BF3 catalyst, while the series of MTFcP (M = Zn, Ni, Co and Cu) were prepared by a metallation reaction between H(2)TFcP and respective metal acetates. All compounds were characterized by UV-vis and MCD spectroscopy, APCI MS and MS/MS methods, high-resolution ESI MS and XPS spectroscopy. Diamagnetic compounds were additionally characterized using H-1 and C-13 NMR methods, while the presence of low-spin iron(II) centers in the neutral compounds was confirmed by Mossbauer spectroscopy and by analysis of the XPS Fe 2p peaks, revealing equivalent Fe sites. XPS additionally showed the influence on Fe 2p binding energies exerted by the distinct central metal ions. The conformational flexibility of ferrocene substituents in H(2)TFcP and MTFcP, was confirmed using variable-temperature NMR and computational methods. Density functional theory predicts that alpha, beta, alpha, beta atropisomers with ruffled porphyrin cores represent minima on the potential energy surfaces of both H2TFcP and MTFcP. The degree of non-planarity is central-metal dependent and follows the trend: ZnTFcP < H(2)TFcP similar to CuTFcP < CoTFcP < NiTFcP. In all cases, a set of occupied, predominantly ferrocene-based molecular orbitals were found between the highest occupied and the lowest unoccupied, predominantly porphyrin-based molecular orbitals. The vertical excitation energies of H2TFcP were calculated at the TDDFT level and confirm the presence of numerous predominantly metal-to-ligand charge-transfer bands coupled via configurational interaction with expected intra-ligand p pi-pi* transitions

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_2TFcP [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_2TFcP. 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_6F_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_2N = N-butyl-N'-methylimidazolium bis(trifluoromethanesulfonyl)imide) were used. Spectroelectrochemical oxidation of H_2TFcP in o-DCB or DCM with TFAB as the supporting electrolyte allowed for characterization of the mixed-valence [H_2TFcP]^+, [H_2TFcP]^(2+), and [H_2TFcP]^(3+) compounds by UV-vis spectroscopy in addition to the "all-Fe(III)" [H_2TFcP]^(4+). The chemical oxidation of H_2TFcP was tested using a variety of oxidants which resulted in formation of mixed-valence [H_2TFcP]^+ and [H_2TFcP]^(2+) as well as [H_2TFcP]^(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_2TFcP]^+ and [H_2TFcP]^(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_2TFcP]^+ and [H_2TFcP]^(2+) complexes was further confirmed by Mossbauer, IR, and XPS data