title: Tricyclometalated iridium complexes as highly stable photosensitizers for light-induced hydrogen evolution.
abstract: The development of an efficient and stable artificial photosensitizer for visible-light-driven hydrogen production is highly desirable. Herein, a new series of charge-neutral, heteroleptic tricyclometalated iridium(III) complexes, [Ir(thpy)2(bt)] (1-4; thpy = 2,2'-thienylpyridine, bt = 2-phenylbenzothiazole and its derivatives), were systematically synthesized and their structural, photophysical, and electrochemical properties were established. Three solid-state structures were studied by X-ray crystallographic analysis. This design offers the unique opportunity to drive the metal-to-ligand charge-transfer (MLCT) band to longer wavelengths for these iridium complexes. We describe new molecular platforms that are based on these neutral iridium complexes for the production of hydrogen through visible-light-induced photocatalysis over an extended period of time in the presence of [Co(bpy)3](2+) and triethanolamine (TEOA). The maximum amount of hydrogen was obtained under constant irradiation over 72 h and the system could regenerate its activity upon the addition of cobalt-based catalysts when hydrogen evolution ceased. Our results demonstrated that the dissociation of the [Co(bpy)3](2+) catalyst contributed to the loss of catalytic activity and limited the long-term catalytic performance of the systems. The properties of the neutral complexes are compared in detail to those of two known non-neutral bpy-type complexes, [Ir(thpy)2(dtb-bpy)](+) (5) and [Ir(ppy)2(dtb-bpy)](+) (6; ppy = 2-phenylpyridine, dtb-bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl). This work is expected to contribute toward the development of long-lasting solar hydrogen-production systems.
authors.affiliation: National Laboratory of Solid State Microstructures and Eco-Materials and Renewable Energy Research Center, Department of Materials Science and Engineering, Nanjing University and Kunshan Innovation Institute of Nanjing University, No. 22, Hankou Road, Nanjing, Jiangsu 210093, PR China.
authors.forename: Yong-Jun
authors.initials: YJ
authors.lastname: Yuan
authors.forename: Zhen-Tao
authors.initials: ZT
authors.lastname: Yu
authors.forename: Hong-Lin
authors.initials: HL
authors.lastname: Gao
authors.forename: Zhi-Gang
authors.initials: ZG
authors.lastname: Zou
authors.forename: Chao
authors.initials: C
authors.lastname: Zheng
authors.forename: Wei
authors.initials: W
authors.lastname: Huang