Molecular Seesaw: How Increased Hydrogen Bonding Can Hinder Excited-State Proton Transfer
Abstract
A previously unexplained effect in the relative rate of excited-state intramolecular proton transfer (ESIPT) in related indole derivatives is investigated using both theory and experiment. Ultrafast spectroscopy [J. Phys. Chem. A, 2015, 119, 5618–5625] found that although the diol 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole exhibits two equivalent intramolecular hydrogen bonds, the ESIPT rate associated with tautomerization of either hydrogen bond is a factor of 2 slower than that of the single intramolecular hydrogen bond in the ethoxy-ol 1,3-bis(2-pyridylimino)-4-ethoxy-7-hydroxyisoindole. Excited-state electronic structure calculations suggest a resolution to this puzzle by revealing a seesaw effect in which the two hydrogen bonds of the diol are both longer than the single hydrogen bond in the ethoxy-ol. Semiclassical rate theory recovers the previously unexplained trends and leads to clear predictions regarding the relative H/D kinetic isotope effect (KIE) for ESIPT in the two systems. The theoretical KIE predictions are tested using ultrafast spectroscopy, confirming the seesaw effect.
Additional Information
© 2016 American Chemical Society. Received: June 23, 2016; Accepted: August 24, 2016; Publication Date (Web): August 24, 2016. The authors thank Stuart Althorpe and Feizhi Ding for helpful discussions. T.F.M. acknowledges financial support from the National Science Foundation (NSF) CAREER Award under Grant CHE-1057112 and the U.S. Department of Energy under Grant DE-SC0006598. R.W. acknowledges financial support from the Deutsche Forschungsgemeinschaft (WE 5762/1-1). E.D. and J.M.D. acknowledge financial support from the AFOSR YIP Award (FA9550-13-1-0128). This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors declare no competing financial interest.Attached Files
Supplemental Material - jz6b01391_si_001.pdf
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Additional details
- Eprint ID
- 70190
- Resolver ID
- CaltechAUTHORS:20160907-091836417
- NSF
- CHE-1057112
- Department of Energy (DOE)
- DE-SC0006598
- Deutsche Forschungsgemeinschaft (DFG)
- WE 5762/1-1
- Air Force Office of Scientific Research (AFOSR)
- FA9550-13-1-0128
- Department of Energy (DOE)
- DE-AC02-05CH11231
- Created
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2016-09-07Created from EPrint's datestamp field
- Updated
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2021-11-11Created from EPrint's last_modified field