Perfluorinated Zinc Porphyrin Sensitized Photoelectrosynthetic Cells for Enhanced TEMPO-Mediated Benzyl Alcohol Oxidation

Gabriele Di Carlo; Cecilia Albanese; Alessandra Molinari; Stefano Carli; Roberto Argazzi; Alessandro Minguzzi; Francesca Tessore; Edoardo Marchini; Stefano Caramori

doi:10.1021/acsami.3c19157

Perfluorinated Zinc Porphyrin Sensitized Photoelectrosynthetic Cells for Enhanced TEMPO-Mediated Benzyl Alcohol Oxidation

ACS Appl Mater Interfaces. 2024 Mar 27;16(12):14864-14882. doi: 10.1021/acsami.3c19157. Epub 2024 Mar 14.

Authors

Gabriele Di Carlo¹, Cecilia Albanese¹, Alessandra Molinari², Stefano Carli³, Roberto Argazzi⁴, Alessandro Minguzzi^{1

5}, Francesca Tessore¹, Edoardo Marchini², Stefano Caramori²

Affiliations

¹ Department of Chemistry, University of Milano, INSTM RU, Via Golgi 19, Milano 20133, Italy.
² Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari 46, Ferrara 44121, Italy.
³ Department of Environmental and Prevention Sciences, University of Ferrara, Via L. Borsari 46, Ferrara 44121, Italy.
⁴ CNR-ISOF c/o Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari 46, Ferrara 44121, Italy.
⁵ Dipartimento di Energia, Politecnico di Milano, Via Lambruschini 4a, Milano 20156, Italy.

PMID: 38483816
DOI: 10.1021/acsami.3c19157

Abstract

This research introduces a novel series of perfluorinated Zn(II) porphyrins with positive oxidation potentials designed as sensitizers for photoelectrosynthetic cells, with a focus on promoting the oxidation of benzyl alcohol (BzOH) mediated by the 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) organocatalyst. Three dyes, CLICK-3, CLICK-4, and BETA-4, are meticulously designed to explore the impact of substituents and their positions on the perfluorinated porphyrin ring in terms of redox potentials and energy level alignment when coupled with SnO₂/TiO₂-based photoanodes and TEMPO mediator. A comprehensive analysis utilizing spectroscopy, electrochemistry, photophysics, and computational techniques of the dyes in solution and sensitized thin films unveils an enhanced charge-separation character in the 4D-π-1A type BETA-4. Incorporating four dimethylamino donor groups at the periphery of the porphyrin ring and a BTD-accepting linker at the β-pyrrolic position equips the structure with a more efficient donor-acceptor system. This enhancement ensures improved light-harvesting capacity, resulting in a doubled incident photon-to-current conversion efficiency (IPCE% ≃30%) in the presence of LiI compared to meso-substituted dyes CLICK-3 and CLICK-4. Sensitizing SnO₂/TiO₂ thin films with BETA-4 successfully promotes the photooxidation of benzyl alcohol (BzOH) in the presence of the rapid TEMPO radical catalyst, yielding photocurrents of approximately 125 μA/cm² in an optimized TBPy/LiClO₄/ACN electrolyte. Notably, when lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) replaces TBPy as the base for TEMPO-catalyzed BzOH oxidation, a remarkable photocurrent of around 800 μA/cm² is achieved, marking one of the highest values reported for this photoelectrochemical reaction to date. This study underscores that the proper functionalization of perfluorinated zinc porphyrins positions these dyes as ideal candidates for sensitizing SnO₂/TiO₂ in the photodriven oxidation of BzOH. It also highlights the crucial role of carefully tuning electrolyte composition based on the electronic properties of molecular sensitizers.

Keywords: artificial photosynthesis; dye-sensitized photoelectrosynthetic cell; photo-oxidation; porphyrins; solar energy conversion.