NDLI: Accelerating slow excited state proton transfer

Content Provider	PubMed Central
Author	Stewart, David J. Concepcion, Javier J. Brennaman, M. Kyle Binstead, Robert A. Meyer, Thomas J.
Abstract	Visible light excitation of the ligand-bridged assembly [(bpy)2Rua II(L)Rub II(bpy)(OH2)4+] (bpy is 2,2′-bipyridine; L is the bridging ligand, 4-phen-tpy) results in emission from the lowest energy, bridge-based metal-to-ligand charge transfer excited state (L−•)Rub III-OH2 with an excited-state lifetime of 13 ± 1 ns. Near–diffusion-controlled quenching of the emission occurs with added HPO4 2− and partial quenching by added acetate anion (OAc−) in buffered solutions with pH control. A Stern–Volmer analysis of quenching by OAc− gave a quenching rate constant of k q = 4.1 × 108 M−1⋅s−1 and an estimated pKa* value of ∼5 ± 1 for the [(bpy)2Rua II(L•−)Rub III(bpy)(OH2)4+]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)2Rua II(L)Rub II(bpy)(OH)3+] in a H2PO4 −/HPO4 2− buffer, back proton transfer occurs from H2PO4 − to give [(bpy)2Rua II(L)Rub(bpy)(OH2)4+] with k PT,2 = 4.4 × 108 M−1⋅s−1. From the intercept of a plot of k obs vs. [H2PO4 −], k = 2.1 × 106 s−1 for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pKa values intermediate between pKa(H3O+) = −1.74 and pKa(H2O) = 15.7.
Related Links	http://dx.doi.org/10.1073/pnas.1220742110
Ending Page	880
Page Count	5
Starting Page	876
File Format	PDF
ISSN	00278424
e-ISSN	10916490
Journal	Proceedings of the National Academy of Sciences of the United States of America
Issue Number	3
Volume Number	110
Language	English
Publisher	National Academy of Sciences
Publisher Date	2013-01-15
Access Restriction	Open
Rights Holder	National Academy of Sciences
Subject Keyword	General Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Multidisciplinary

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
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3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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