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

Ron Simkovitch, Shay Shomer, Rinat Gepshtein, Michal E. Roth, Doron Shabat, Dan Huppert

Research output: Contribution to journalArticlepeer-review

Abstract

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 k PT 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. k PT 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.

Original languageEnglish
Pages (from-to)90-101
Number of pages12
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume277
DOIs
StatePublished - 1 Mar 2014

Keywords

  • Fast reactions
  • Photoacids
  • Protic solvents
  • Proton transfer
  • Quinone cyanine

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