Towards Hydrogen Evolution Initiated by LED Light: 2-(1H-1,2,3-Triazol-4-yl)pyridine-Containing Polymers as Photocatalyst

• Published in: Macromolecular rapid communications. 2015-04, Vol.36 (7), p.671-677
• Main Authors: Happ, Bobby, Kübel, Joachim, Pfeffer, Michael G., Winter, Andreas, Hager, Martin D., Dietzek, Benjamin, Rau, Sven, Schubert, Ulrich S.
• Format: Article
• Language: English
• Subjects: Addition polymerization; Catalysis; Chain transfer; Copolymers; energy transfer; hydrogen; Hydrogen - chemistry; Hydrogen evolution; iridium complexes; Macromolecules; metallopolymers; Models, Molecular; Photocatalysis; Photosensitizing Agents - chemical synthesis; Photosensitizing Agents - chemistry; Platinum; Polymerization; Polymers; Polymers - chemical synthesis; Polymers - chemistry; Pyridines - chemistry; Rafts; Triazoles - chemistry
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.201400672

Two‐ and three‐component polymethacrylates, featuring a 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine‐based metal complex as photosensitizer, a viologen‐type electron mediator, and a triethylene glycol methyl ether as solubilizing part are synthesized by statistical reversible addition–fragmentation chain transfer (RAFT) radical polymerization allowing the construction of well‐defined copolymers. Thereby, heteroleptic ruthenium(II) and iridium(III) complexes serve as charged photosensitizers. In hydrogen evolution experiments, as proof‐of‐concept, triethylamine is utilized as a sacrificial donor and colloidal platinum as hydrogen evolving catalyst. The macromolecules bearing heteroleptic iridium(III) complexes of the general formula [Ir(ppy)2(trzpy)]PF6 (ppy: 2‐phenylpyridine; trzpy: 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine) and [Ir(btac)2(trzpy)]PF6 (btac: 3‐(2‐benzothiazolyl)‐7‐(diethylamino)coumarin) are photocatalytically active producing molecular hydrogen in water upon illumination at 470 nm. By changing the cyclometalating ligand from ppy to btac, the photocatalytic performance of the copolymer as reflected in the turnover number increases by two orders of magnitude. Metal‐containing metallopolymers are investigated as sensitizers in the light‐induced Pt‐catalyzed hydrogen production. Well‐defined water‐soluble copolymers can be obtained by applying a controlled polymerization technique (reversible addition–fragmentation chain transfer poly­merization, RAFT). The iridium‐containing systems are superior to their ruthenium‐containing analogs with respect to the formation of molecular hydrogen.