Zinc Porphyrin Metal‐Center Exchange at the Solid–Liquid Interface

Abstract

Demetalation of zinc 5,10,15,20-tetraphenylporphyrin (ZnTPP) under acidic conditions and ion exchange with Cu(2+) ions at neutral pH are both rapid reactions in the liquid medium. However, for ZnTPP monolayers adsorbed on a Au(111) surface exposed to aqueous solution, we find that, although ion exchange takes place rapidly as expected, demetalation does not occur, even at pH values as low as 0. Based on this, we conclude that metal center exchange on the surface does not proceed through a free-base porphyrin as an intermediate. Furthermore, once formed, CuTPP is stable on the surface and the reverse exchange from CuTPP to ZnTPP in the presence of Zn(2+) ions could not be achieved. The preference for copper is so strong that even an attempt to exchange adsorbed ZnTPP with Ni(2+) ions in the presence of traces of Cu(2+) yielded CuTPP rather than NiTPP.

Beyond Nanoparticles: The Role of Sub-nanosized Metal Species in Heterogeneous Catalysis

“…Porphyrin-related macrocycles are also able to stabilize different atoms or ions on the surface. Their surface can modified with co-deposited metal atoms, substrate metal atoms and oxide lattice ions [75,76]. Their catalytic application is well-documented in a recent review [77].…”

On-surface transmetalation of metalloporphyrins

“…25,26 A third study describes the exchange of Zn by Cu at the solid/ liquid interface. 27 No clear trends can be extracted from the existing literature: on the one hand Franke et al 27 report Zn substitution by Cu in a tetraphenylporphyrin network at the solid-liquid interface. On the other hand Shi et al 28 report no such substitution of Zn-tetrapyridylporphyrin and co-deposited Cu in vacuum.…”

Biosynthesis of organic photosensitizer Zn-porphyrin by diphtheria toxin repressor (DtxR)-mediated global upregulation of engineered heme biosynthesis pathway in Corynebacterium glutamicum

“…Porphyrins functioning as photo-electrochemical materials are of particular interest in a range of areas related to solar cell technology, battery chemistry, solid/liquid interfaces and biomedical research because of their functional and structural properties that incorporate a metal ion in the center and have great absorption bands in the visible spectrum 1 – 7 . In particular, Zn-porphyrin derivatives have recently attracted much attention for their great potential application as a promising raw material for sensitizing an organic solar cell in a photovoltaic system that harvests light to convert solar energy into electricity, or in catalyzing multistep reactions at interface 3 , 4 , 8 – 13 . In addition to electronic and physicochemical applications, Zn-porphyrins have been studied as photosensitizers for their antitumor and antibacterial activity in photodynamic therapy-mediated biomedical applications 14 .…”