Temperature dependence of the excited-state proton-transfer reaction of quinone-cyanine-7

Ron Simkovitch, Shay Shomer, Rinat Gepshtein, Doron Shabat, Dan Huppert*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Steady-state and time-resolved fluorescence techniques were used to study the temperature dependence of the photoprotolytic process of quinone-cyanine-7 (QCy7), a very strong photoacid, in H2O and D2O ice, over a wide temperature range, 85-270 K. We found that the excited-state proton-transfer (ESPT) rate to the solvent decreases as the temperature is lowered with a very low activation energy of 10.5 ± 1 kJ/mol. The low activation energy is in accord with free-energy-correlation theories that predict correlation between ΔG of reaction and the activation energy. At very low temperatures (T < 150 K), we find that the emission band of the RO-, the deprotonated form of QCy7, is blue-shifted by ∼1000 cm-1. We attributed this band to the RO -···H3O+ ion pair that was suggested to be an intermediate in the photoprotolytic process but has not yet been identified spectroscopically.

Original languageEnglish
Pages (from-to)3925-3934
Number of pages10
JournalJournal of Physical Chemistry A
Volume117
Issue number19
DOIs
StatePublished - 16 May 2013

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