Competition and interplay of various intermolecular interactions in ultrafast excited-state proton and electron transfer reactions.

The main features of the photoinduced kinetics of both ultrafast excited-state proton and electron transfer reactions that occur in the picosecond (ps) and femtosecond (fs) time domains are compared. Proton transfer (PT) reaction kinetics can be described in terms of several discrete values of rate coefficients in the form of polyexponential functions where each value of the rate coefficient can be attributed to a definite physical behavior of the reaction mechanism. In contrast, electron transfer (ET) reaction kinetics requires a consideration of a continuous distribution of rate coefficients.

Excited-state proton transfer in N-methyl-6-hydroxyquinolinium salts: solvent and temperature effects.

The excited-state proton transfer (ESPT) reaction of the "super"photoacid N-methyl-6-hydroxyquinolinium (MHQ) was studied using both fluorescence upconversion and time-correlated single photon counting (TCSPC) techniques. The ultrafast ESPT kinetics were investigated in various alcohols and water and determined to be solvent-controlled. The ESPT temperature dependence of MHQ was also studied in various alcohols and compared to that observed for another "super"photoacid, 5,8-dicyano-2-naphthol (DCN2).

Diffusional effects on the reversible excited-state proton transfer. From experiments to Brownian dynamics simulations.

We have studied an excited state proton transfer (ESPT) from the cationic "super" photoacid N-methyl 6-hydroxyquinolinium perfluorobutane sulfonate to non-aqueous solvents using picosecond and nanosecond time-resolved fluorescence spectroscopy. Upon the photoinduced adiabatic deprotonation from the hydroxyl moiety, a quinolinium zwitterion with a highly anisotropic charge distribution is formed. Due to the complexity of the resultant photodissociated system, the typical description of the reversible ESPT within the framework of the Spherically Symmetric Diffusion Problem (SSDP) is not possible.