Solvent dependence of excited-state proton transfer from pyranine-derived photoacids.
Steady-state and time-resolved techniques were employed to study the excited-state proton-transfer (ESPT) rate of two newly synthesized 8-hydroxy-1,3,6-pyrenetrisulfonate (pyranine, HPTS) derived photoacids in three protic solvents, water, methanol and ethanol. The ESPT rate constant k(PT) of tris(1,1,1,3,3,3-hexafluoropropan-2-yl)-8-hydroxypyrene-1,3,6-trisulfonate, 1a, whose pK(a)* ~ -4, in water, methanol and ethanol is 3 × 10(11) s(-1), 8 × 10(9) s(-1) and 5 × 10(9) s(-1) respectively. (8-Hydroxy-N1,N3,N6-tris(2-hydroxyethyl)-N1,N3,N6-trimethylpyrene-1,3,6 trisulfonamide, 1b) is a weaker acid than 1a but still a strong photoacid with pK(a)* ~ -1 and the ESPT rate in water, methanol and ethanol is 7 × 10(10) s(-1), 4 × 10(8) s(-1) and 2 × 10(8) s(-1). We qualitatively explain our kinetic results by a Marcus-like free-energy correlation which was found to have a general form suitable for describing proton transfer reactions in both the proton-adiabatic and the proton-non-adiabatic limits.
Biophysical Chemistry, Saarland University, Campus, Building B2 2, D-66123 Saarbrücken, Germany. g.jung@mx.uni-saarland.de.
Christian
C
Spies
Shay
S
Shomer
Björn
B
Finkler
Dina
D
Pines
Ehud
E
Pines
Gregor
G
Jung
Dan
D
Huppert
D000143:Acids / Q000737:chemistry*; D001190:Arylsulfonates / Q000138:chemical synthesis / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D007700:Kinetics; D000432:Methanol / Q000737:chemistry*; D055668:Photochemical Processes; D011522:Protons; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry*
D000143:Acids; D001190:Arylsulfonates; D011522:Protons; D012997:Solvents; D014867:Water; D000431:Ethanol; C005047:pyranine; D000432:Methanol