pH Control of Intramolecular Energy Transfer and Oxygen Quenching in Ru(II) Complexes Having Coupled Electronic Excited States

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• 作者：Tod A. Grusenmeyer ; Jin Chen ; Yuhuan Jin ; Jonathan Nguyen ; Jeffrey J. Rack ; Russell H. Schmehl
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：May 2, 2012
• 年：2012
• 卷：134
• 期：17
• 页码：7497-7506
• 全文大小：479K
• 年卷期：v.134,no.17(May 2, 2012)
• ISSN：1520-5126

文摘

This work illustrates the control of excited state energy transfer processes via variation of pH in transition metal complexes. In these systems a Ru(II) complex having two carboxylated bipyridyl ligands is covalently linked to pyrene via one of two different pyrene derivitized bipyridyl ligands. The energy of the Ru to carboxy-bipyridine ³MLCT state is pH dependent while the pyrene triplet energy remains unchanged with solution acidity. At pH 0 the ³MLCT state is the lowest energy state, and as the pH is raised and the carboxy-bipyridyl ligands are successively deprotonated, the energy of the ³MLCT state rises above that of the pyrene triplet, resulting in a significant increase in the lifetime of the observed emission. Detailed analysis of ultrafast and microsecond time-resolved excited state decays result in a description of excited state decay that involves initial equilibration of the ³MLCT and pyrene triplet states followed by relaxation to the ground state. The lifetime of excited state decay is defined by the position of the equilibrium, going from 2 渭s at pH 0 to >10 渭s at higher pH as the equilibrium favors the pyrene triplet. In addition, quenching of the excited state by dissolved oxygen exhibits a pH dependence that parallels that of the excited state lifetime. The results illustrate the utility of exploiting excited state equilibria of this type in the development of highly effective luminescent oxygen sensors.