Platinum(II) polypyridyl complexes for visible light-driven hydrogen production from water

Abstract

Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2009.This thesis employs Pt(II) terpyridyl and cyclometalated complexes as the chromophores to construct photoactive systems for hydrogen production from water. Several catalysts, including Pt nanoparticles, Pt(II) bi- and terpyridyl chloro complexes, and cobalt dimethylglyoximate complexes, were investigated to catalyze the hydrogen production reactions. Chapter 1, as an introduction part, describes the recent progress in photoinduced hydrogen production from water, including heterogeneous multiple-component systems, homogeneous multiple-component systems and an integrated approach to artificial photosynthesis for photoinduced hydrogen production. Chapter 2 studies a multiple-component system containing a platinum(II) terpyridyl acetylide chromophore, a sacrificial donor (TEOA), an electron relay (MV2+ and diquats) and colloidal platinum catalyst for photocatalytic generation of hydrogen from water. Hydrogen efficiency varies by using different Pt(II) photosensitizers and electron relays, as well as the different concentrations of each species. Chapter 3 discusses the real role of [Pt(ttpy)Cl]+ and Pt(dcbpy)Cl2 as the hydrogen production catalysts. TEM, EDAX and mecury tests show the Pt(II) chloro complexes are only the precursors to form colloidal platinum, which is the real catalyst for hydrogen generation. Chapter 4 and chapter 5 study a novel homogeneous system for photochemical hydrogen production using a cobalt(III) dimethylglyoximate complex as the hydrogen production catalyst and a Pt(II) terpyridyl acetylide complex as the photosensitizer. Cobalt(III) dimethylglyoximate has been used for hydrogen generation by electrochemical method. But very few examples have been reported in photochemical way. The variation of the photosensitizers and cobaloximes are also discussed, as well as the reaction mechanism. Chapter 6 discusses a novel terpyridyl cationic complex [Pt(TPPPB)Cl]Cl, containing a bulky terpyridyl ligand (1-terpyridyl-2,3,4,5,6-pentaphenyl-benzene (TPPPB)). The complex exhibits reversible vapochromic behavior upon exposure to methylene chloride vapors, changing color from red to green. The shift to higher energy in the emission maximum from 654 nm to 514 nm is the largest vapochromic shift (140 nm) yet reported. The [Pt(TPPPB)Cl]Cl complex exhibits high selectivity for certain volatile organic compounds (VOCs) including only methylene chloride, ethanol, ethyl acetate and acetonitrile. The crystal structures of both the green and red forms have been determined by single crystal X-ray diffraction. Chapter 7 describes the perspectives and future directions in this project. More potential efficient and stable cobalt complexes are designed and discussed. The platinum-cobalt supramolecular assemblies towards photochemical molecular devices show interesting properties for hydrogen production