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Comparison of the rate of excited-state proton transfer from photoacids to alcohols and water

Paper ID Volume ID Publish Year Pages File Format Full-Text
26764 43975 2014 12 PDF Available
Title
Comparison of the rate of excited-state proton transfer from photoacids to alcohols and water
Abstract

•Two very strong photoacids QCy7, pKa*∼−6.5, and QCy9, pKa*∼−8.5, are studied in three protic solvents, water, MeOH and EtOH.•Weak photoacids do not transfer a proton to alcohols within the excited state lifetime, whereas strong photoacids do.•In QCy7 the ESPT rate constant, kPT in water, methanol and ethanol is 1.2 × 1012, 8 × 1011 and 7 × 1011 respectively.•The ESPT rate of QCy9 in these solvents is the same, kPT ∼ 1013 s−1.•Non-adiabatic and adiabatic PT theories explain the kPT solvent dependence of weak and very strong photoacids respectively.

Steady-state and time-resolved techniques were employed to study the excited-state proton-transfer (ESPT) rate of two newly synthesized photoacids – quinone cyanine diindolium (QCy7) and its dipicolinium analog (QCy9) – in three protic solvents, water, methanol and ethanol. The ESPT rate constant kPT of QCy7, whose pKa*∼−6.5 in water, methanol and ethanol is 1.2 × 1013 s−1, 8 × 1011 s−1, 7 × 1011 s−1 respectively. kPT for QCy9 (pKa*∼−8.5), is 1013 s−1 for all three protic solvents used. We qualitatively explain these results and also the previously found solvent dependence of kPT of weaker photoacids by adiabatic and non-adiabatic proton-transfer formalism.

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Keywords
Fast reactions; Proton transfer; Photoacids; Quinone cyanine; Protic solvents
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Comparison of the rate of excited-state proton transfer from photoacids to alcohols and water
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 277, 1 March 2014, Pages 90–101
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us