Fused Porphyrin Thin Films as Heterogeneous Visible-Light Active Photocatalysts with Well-Defined Active Metal Sites for Hydrogen Generation

Abstract

Metalloporphyrin-based photocatalysts have attracted great interest due to their high extinction coefficient in the visible range coupled to a catalytically active central metal ion surrounded by a highly conjugated heterocyclic macrocycle. In this work, fused copper(II) porphyrin-based conjugated polymer thin films are shown to be active electrocatalysts and photocatalysts for the heterogeneous hydrogen evolution reaction (HER). The fused copper(II) porphyrin thin films notably show a significant reduction of the overpotential required for HER in comparison to the reference nonfused porphyrin thin films. More importantly, in-depth high-resolution mass spectrometry reveals how the porphyrin substituents influence the catalytic performance of the films, with phenyl substituents enabling superior photocatalytic performances over mesityl substituents, providing insights for the engineering of heterogeneous catalysts based on fused metalloporphyrins.

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

“…They have been used in applications involving non‐linear optic materials, molecular wires, and supramolecular chemistry [23,24] . Nonetheless, fused porphyrins, and related porphyrinoids featuring extended conjugation, have not been as extensively studied for applications in electrocatalysis [25,26] . Further, although there are reported examples of doubly‐ and triply‐fused dimers, trimers, and oligomeric porphyrin arrays containing Mg, [27] Co, [28] Ni, [22,29–42] Cu, [34–36,38–40,43–47] Zn, [28,30,31,36,38–40,44,45,47–57] Ru, [58] Pd, [29,34–36,38,50] Ag, [46] Pb, [57] Y, [59] and Tb, [59] analogous multinuclear Fe fused porphyrin complexes, which could be useful for applications in electrocatalysis, have yet to be reported.…”

Electronic and energy level engineering of directly fused porphyrin-conjugated polymers – impact of the central metal cation

“…8 Directly fused porphyrin assemblies are also active catalysts. 14,15 In particular, bimetallic copper(II)-fused porphyrin dimers were shown to be a highly active HER catalyst, demonstrating the direct fusion of the porphyrin macrocycles to be a promising strategy for enhanced electrocatalyst design. 14 More recently, electrochemical and spectroscopic investigations on fused iron(III) porphyrin complexes revealed their ability to store up to six electrons, added to the capability of the p-extended ligand to delocalize electrons across the multimetallic scaffold.…”

“…20 Preliminary studies carried out by our group on the electro-and photocatalytic activity of directly fused copper(II) porphyrin conjugated polymer thin films for the heterogeneous HER showed that the phenyl substituent, enabling intramolecular cyclization, promotes superior catalytic performance over the mesityl substituent. 15 Besides the dehydrogenative intermolecular coupling (polymerization) forming triple, double or single linkages between the porphyrin units and the dehydrogenative intramolecular coupling (cyclization), other side reactions can take place during the oCVD reaction of porphyrins. Namely, the chlorination of the macrocycle and the substituents, the demetallation and potential re-metalation of the porphyrin core, and oxidation of the central metal cation can take place (Scheme 1).…”

“…With the aim of elucidating the direct and indirect (regioselectivity of the polymerization) influence of the central metal cation on the band gap and band edge positions of directly fused porphyrin-conjugated polymers, we studied the oCVD reaction of 5,15-diphenyl metalloporphyrins (MDPP; M = Co(II), Cu(II), Mg(II), Zn(II), Pd(II), Pt(II), Ag(II), Ru(II), Ag(II), and Fe(III) Cl). Phenyl was selected as the meso-substituent due to the superior catalytic 15 and sensing properties 24 of poly(5,15diphenyl metalloporphyrin) thin films over poly(5,15-dimesityl metalloporphyrin) ones. The occurrence of intermolecular coupling and other side reactions during oCVD was evidenced by ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy, laser desorption ionization high-resolution mass spectrometry (LDI-HRMS), and X-ray photoelectron spectroscopy (XPS) analysis.…”

Metal Complexes of Singly, Doubly and Triply Linked Porphyrins and Corroles: An Insight into the Physicochemical Properties

“…Recent publications from Boscher and co-workers reported on a doubly fused Cu(II)-containing porphyrin thin film which was shown to be an active electrocatalysts and photocatalysts towards heterogeneous HER. [47] The fused porphyrin thin films notably reduced the overpotential for HER in comparison to the respective nonfused porphyrin thin films suggesting efficient separation and storage of multiple charges due to extension of π-electron conjugation. Further studies involving different substituents at the peripheral position (phenyl and mesityl) of the fused porphyrin suggested influence of functional groups on the superior catalytic activity of the bis-metalloporphyrin thin films.…”