The excitation behaviors for 4′-N,N-diethylamino-3-hydroxyflavone (Ia) have been investigated via femtosecond fluorescence upconversion approaches to gain detailed insights into the mechanism of the proton/chargetransfer coupling reaction. In polar solvents such as CH 2 Cl 2 and CH 3 CN, in addition to a slow, solventpolarity-dependent rate (a few tens of picoseconds -1 ) of excited-state intramolecular proton transfer (ESIPT) reported previously, early femtosecond relaxation dynamics clearly reveal that the proton-transfer tautomer emission consists of a rise component of a few hundred femtoseconds. The temporal spectral evolution at the time domain of zero to a few hundred femtoseconds further resolves two distinct emission bands consisting of a proton-transfer tautomer emission and a time-dependent Stokes shifted emission. The results, in combination with ab initio calculations on the dipolar vectors for normal and tautomer species, lead us to unveil the importance of the relationship of the dipolar vectors among various states, and hence the corresponding solvation energetics in the overall ESIPT reaction. We conclude a similar dipolar character between ground-state normal (N) and excited proton-transfer tautomer (T*) species, whereas due to the excited-state intramolecular charge transfer (ESICT), the normal excited state (N*) possesses a large dipolar change with respect to N and T*. ESIPT is thus energetically favorable at the Franck-Condon excited N*, and its rate is competitive with respect to the solvation relaxation process. After reaching the solvent equilibration, there exists an equilibrium between N* and T* states in, for example, CH 3 CN. Due to the greatly different equilibrium polarization between N* and T*, both forward and reversed ESIPT dynamics are associated with a solvent-induced barrier. The latter viewpoint of the equilibrium type of ESIPT in Ia is in agreement with the previous reports based on steady-state, 8 picosecond, 9,13 and femtosecond 14,15 dynamic approaches.

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Collision-induced dissociation (CID) of sodiated glucose was investigated using electronic structure calculations and resonance excitation in a low-pressure linear ion trap. The major dissociation channels in addition to desodiation are dehydration and CHO elimination reactions which the barrier heights are near to or lower than the sodiation energy of glucose. Dehydration reaction involves the transfer of the H atom from the O2 atom to the O1 atom, followed by the cleavage of the C1-O1 bond. Notably, α-glucose has a dehydration barrier lower than that of β-glucose. This difference results in the larger branching ratio of dehydration reactions involving α-glucose, which provides a simple and fast method for identifying the anomeric configurations of glucose. The CHO elimination starts from the H atom transfer from the O1 atom to the O0 atom, followed by the cleavage of the C1-O0 bond. These results were further confirmed by experimental study using O-isotope-labeled compounds. Both the experimental data and theoretical calculations suggest that the dehydration reaction and cross-ring dissociation of sodiated carbohydrates mainly occur at the reducing end during low-energy CID.