Expanding the Redox Range of Surface-Immobilized Metallocomplexes Using Molecular Interfaces

Abstract

Rationally designed material interfaces offer opportunities to control matter and energy across multiple length scales, yet remain challenging to synthetically prepare. Inspired by nature, where amino acid residues and softmaterial coordination environments regulate the midpoint potentials of metals in proteins, thin-film polymeric coatings have been developed to assemble molecular components, including catalysts, onto solid-state (semi)conducting surfaces. In this report, we describe the immobilization of metalloporphyrins onto transparent conductive oxide supports using either direct grafting to the oxide surface or coordination to an initially applied thin-film polypyridyl coating. The composite materials enable direct measurements of electrochemical and optical properties associated with the surface-immobilized components. Despite the similarity of the core cobalt porphyrin units used in assembling these hybrid architectures, the redox potentials assigned to the Co III/II relays span a 350 mV range across the distinct constructs. This range in redox potential is extended to 960 mV when including comparisons to constructs utilizing polymer-immobilized cobaloxime catalysts in place of cobalt porphyrins, where reduction of the cobaloximes requires significantly more-negative bias potentials. This work illustrates the use of soft-material interfaces for assembling molecularmodified electrodes where the nanoscale connectivity of the surface coatings determines the electrochemical properties of the macroscopic assemblies.

Six‐Electron Chemistry of a Binuclear Fe(III) Fused Porphyrin

“…In general, this vibrational mode is sensitive to both the elemental nature of the porphyrin metal center and its local coordination environment [61–64] . For these reasons, in‐plane porphyrin deformation vibrations have been used as diagnostic signals for indicating the presence of metalloporphyrins on surfaces and gaining information on their local chemical environments [25,60,65–68] . In this report, the difference in ν Fe‐N frequencies of [FeTTP]Cl and [Fe 2 FP]Cl 2 suggests the fused complex provides a more rigid ligand motif.…”

Photoelectrochemical Water Oxidation by Cobalt Cytochrome C Integrated-ATO Photoanode

“…A previously established sol−gel route for producing highly mesoporous ATO coatings was adapted for the fabrication of macroporous ATO coatings [26,38,40,45,46]. Briefly, a clear solution with 1.00 g of SnCl 4 •5H 2 O (Alfa Aesar, 98%) (Haverhill, MA, USA) and 0.05 g of SbCl 3 (Alfa Aesar, ≥99.9%) in 6.50 g of n-BuOH and 1.0 g of deionized water was prepared and cooled to about 4 • C in ice bath, and then transferred into an Ultra-Turrax tube drive with a rotor stator element.…”

“…We previously demonstrated that wild type (WT) cyt c could be absorbed in thin films of highly mesoporous ATO with retention of its native structure and redox properties [36]. Moreover, cobalt porphyrins have been previously interfaced with TCOs and other semiconductors [37][38][39]. The immobilization strategy for binding cyt c to ATO takes advantage of the electrostatic interaction between substantial negative charges on the metal oxide surface and the protein's positively charged surface, mediated by lysine residues [40,41].…”

Water‐Soluble Polymers with Appending Porphyrins as Bioinspired Catalysts for the Hydrogen Evolution Reaction

“…Inspired by nature, we herein report the design and catalytic HER features of three water‐soluble polymers with appending Co porphyrin units and different side‐chain groups (Figure ). Polymers have been reported to enhance electrocatalysis and photocatalysis recently . Apart from significantly improved water solubility, porphyrin units are protected by polymer chains to avoid their degradation via oxidative oligomerization .…”