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.
|Number of pages||12|
|Journal||Journal of Photochemistry and Photobiology A: Chemistry|
|State||Published - 1 Mar 2014|
- Fast reactions
- Protic solvents
- Proton transfer
- Quinone cyanine