Subscriber access provided by GAZI UNIV
Article
Solvation Dynamics and Proton Transfer in Diethylaminohydroxyflavone Christopher A Rumble, Jens Breffke, and Mark Maroncelli J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.6b12146 • Publication Date (Web): 21 Dec 2016 Downloaded from http://pubs.acs.org on December 27, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Physical Chemistry B is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 26
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
Solvation Dynamics and Proton Transfer in Diethylaminohydroxyflavone Christopher Rumble(a), Jens Breffke(a,b), and Mark Maroncelli* Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
Abstract: 4’-N,N-diethylamino-3-hydroxyflavone (DEAHF) exhibits dual fluorescence in most solvents as a result of a rapid excited-state intramolecular proton transfer reaction. The high sensitivity of its dual emission to solvent polarity and hydrogen bonding make DEAHF of interest as a ratiometric fluorescence sensor. In addition, prior work has suggested that the rate of this proton transfer should depend on solvent relaxation in an unusual manner. In particular, it is proposed that rapid solvation of the initially excited reactant should retard reaction. The present work tests this idea by using femtosecond Kerr-gated emission spectroscopy to measure the reaction kinetics of DEAHF in mixtures of propylene carbonate (PC) + acetonitrile (ACN). This mixture was chosen to maintain constant solvent polarity and thereby constant reaction energies while varying solvation times ~10-fold with composition. The reaction kinetics observed in these mixtures are multi-exponential, consisting of resolvable components of ~2 ps and ~30 ps and a small fraction of reaction faster than detectable by the 400 fs resolution of the experiment. Average reaction times increase by approximately a factor of 2 as a function of ACN mole fraction, primarily as a result of changes to the slower component. This trend is opposite to the composition dependence of solvation times, thereby supporting the unusual role of polar solvation dynamics in this proton transfer. In n-alkane solvents, where electrostatic coupling is minimized, frictional properties of the solvent do not influence reaction rates.
________________________________ (a) Equal contributors. (b) Current address: National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899-8372 * Corresponding author,
[email protected] 1 ACS Paragon Plus Environment
The Journal of Physical Chemistry
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 26
1. Introduction Excited-state intramolecular proton transfer (ESIPT) reactions, especially those resulting in dual fluorescence, have long served as model systems for probing of the kinetics of fast proton transfer.1,2 Recent interest has focused more on using such reactions in applications such as ratiometric sensing3,4 and creation of functional materials.5 In cases where electronic excitation entails substantial charge redistribution, as in proton coupled electron transfer reactions,6 one often observes large solvent effects.4 In the present study, we use time-resolved fluorescence spectroscopy to observe ESIPT in 4’-N,N-diethylamino-3-hydroxyflavone (DEAHF, Figure 1) in order to help clarify the role that solvation dynamics plays in determining its ESIPT rate. In the ground electronic state, DEAHF exists only in the “normal” (N) form. Excitation to the S1 state produces N*, from which reaction to the “tautomer” S1 state (T*) is accessible. In contrast to the
