In six of seven cases, direct anodic oxidation of the ethynyl group of an ethynylphenylderivatized free-base porphyrin gave modified glassy carbon electrodes in which the porphyrin was strongly surface-bound, most likely in a perpendicular geometry through covalent attachment of the ethynyl group to a surface carbon atom. The porphyrins each contained an ethynylphenyl group in one meso position and varied in the groups present in the other three meso positions. Electrografted 5,10,15,20-tetrakis(ethynylphenyl)porphyrin, H21, which has ethynyl moieties in all four meso positions, has well-defined surface voltammetry and grows to multi-layer levels upon repeated cyclic voltammetry (CV) deposition scans. Multi-layering was not observed to the same degree for mono-ethynylphenyl-substituted porphyrins, and became progressively less for porphyrins having groups in the 15-meso position that were more protective against ethynyl radical attack. Clean molecular monolayer-level coverage was observed for 5-ethynylphenyl-10,20-bis(3-methoxyphenyl)-15-hexylporphyrin, H25. Owing to the fact that the ethynyl oxidation potential (1.1 to 1.5 V vs ferrocene) is more positive than that of the second macrocycle oxidation, the longevities and follow-up reactions of the porphyrin dications were also studied by CV, chemical oxidation, and optical spectroscopy in homogeneous solution. The primary follow-up products of the doubly oxidized porphyrins, whether surface-bound or in solution, were pyrrole-protonated species that were easily reduced back to the neutral porphyrin.

Two ethynyl-derivatized isomers of bis(fulvalene)diiron (BFD, 1,1'-biferrocenylene) were prepared and covalently attached to glassy carbon electrodes through their ethynyl group by three different electrode modification methods. Cyclic voltammetry and square wave (SW) voltammetry were used to characterize surface coverages of 1.4-5.5 × 10 mol cm, the higher of these corresponding to roughly a monolayer, based on computation of an idealized close-packing structure for ethynylbis(fulvalene)diiron (E-BFD) on a solid surface. In a dichloromethane solution containing a smaller electrolyte anion such as [PF] or [ClO], the E-BFD-modified electrodes exhibited two quasi-Nernstian one-electron oxidations. In contrast, the current for the second oxidation process, [E-BFD], was diminished in electrolytes containing one of the large fluoroaryl borate anions, [B(CF)] or [B(CH(CF))]. The effect was enhanced for electrodes having higher surface coverages being probed at shorter voltammetric time scales. SW voltammetry showed that the diminished currents for [E-BFD] in large-anion electrolytes are not caused by slow electron transfer. Rather, they are attributed to mixed diffusivity of the counter-anions at the electrode/solution interface, as [E-BFD] and the anion form the optimum (lowest-energy) configuration of a 1:1 ion pair. The interior transport of the anion required to reach this configuration may be sterically encumbered, accounting for the diminished charge transfer observed with electrolytes containing large anions.

The oxidation of [n]nickelocenophanes [Ni(η 5 -C 5 H 4 ) 2 (CH 2 ) 3 ] (3), [Ni(η 5 -C 5 H 4 ) 2 (SiMe 2 ) 2 ] (10 12), and poly-(nickelocenylpropylene) [Ni(η 5 -C 5 H 4 ) 2 (CH 2 ) 3 ] n (4) to both the monocationic and dicationic species was investigated in dichloromethane by cyclic voltammetry (CV) and square-wave voltammetry. The presence of acetonitrile on the oxidation potentials of 3 in dichloromethane was also investigated by CV. The [n]nickelocenophanes 3 and 10−12 exhibited two single-electron Nernstian redox processes, and the monocations [3] + , [10] + , [11] + , and [12] + were isolable as [B(C 6 F 5 ) 4 ] − salts after chemical oxidation, and were structurally characterized. Ni−Cp cent distances in all four monomers decreased upon oxidation, with a structural distortion manifested in the ring-tilt angle, α, among other angles. CV studies of the reversible first oxidation process to the polyelectrolyte {[Ni(η 5 -C 5 H 4 ) 2 (CH 2 ) 3 ] + } n ([4] n+ ) were used to estimate the molecular weight of the polymeric material (M w = 5300 g mol −1 ) by comparing its diffusion coefficient with that of a monomeric analogue, and the second electrochemical oxidation of polymer 4 was found to be only partially chemically reversible.