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Photocatalytic Hydrogen Evolution with a Self‐Assembling Reductant–Sensitizer–Catalyst System
Author(s) -
Natali Mirco,
Argazzi Roberto,
Chiorboli Claudio,
Iengo Elisabetta,
Scandola Franco
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201300133
Subject(s) - photochemistry , catalysis , chemistry , photocatalysis , turnover number , quantum yield , photosensitizer , quenching (fluorescence) , porphyrin , aqueous solution , electron donor , ascorbic acid , organic chemistry , fluorescence , physics , food science , quantum mechanics
A noble‐metal‐free system for photochemical hydrogen production is described, based on ascorbic acid as sacrificial donor, aluminium pyridyl porphyrin as photosensitizer, and cobaloxime as catalyst. Although the aluminium porphyrin platform has docking sites for both the sacrificial donor and the catalyst, the resulting associated species are essentially inactive because of fast unimolecular reversible electron‐transfer quenching. Rather, the photochemically active species is the fraction of sensitizer present, in the aqueous/organic solvent used for hydrogen evolution, as free species. As shown by nanosecond laser flash photolysis experiments, its long‐lived triplet state reacts bimolecularly with the ascorbate donor, and the reduced sensitizer thus formed, subsequently reacts with the cobaloxime catalyst, thereby triggering the hydrogen evolution process. The performance is good, particularly in terms of turnover frequencies (TOF=10.8 or 3.6 min −1 , relative to the sensitizer or the catalyst, respectively) and the quantum yield ( Φ =4.6 %, that is, 9.2 % of maximum possible value). At high sacrificial donor concentration, the maximum turnover number (TON=352 or 117, relative to the sensitizer or the catalyst, respectively) is eventually limited by hydrogenation of both sensitizer (chlorin formation) and catalyst.