Ultrafast experiments on electron transfer

Aqueous Solvation Dynamics at the Anionic Surfactant Air/Water Interface

“…The surfactant-free air/water interface was studied previously, 22,23 and two components, τ 1 ) 250 ( 60 fs and τ 2 ) 1250 ( 80 fs were obtained, with an amplitude-averaged solvation time of τ s ) 850 ( 50 fs. These time scales are similar to the relaxation time scales observed in the bulk water 2,19,25 in agreement with the predictions of the dielectric continuum theory. 15 (Due to the limited time resolution, the ultrafast "inertial" component of the solvation dynamics in water, on the <30 fs time scale 25 , was not recorded in these experiments.)…”

“…The ground state contribution is timeindependent. Assuming a two-level model (i.e., only two electronic states resonantly contribute to the SHG), where the first term describes the ground-state resonant contribution (2) g , the second term is the excited-state resonant contribution (2) e , and the third term is nonresonant nonlinear susceptibility (2) NR ; n g and n e represent fractions of the C314 molecules in the ground and excited states, n g + n e ) 1. Because the second harmonic generation is a coherent optical process, the three contributions interfere constructively or destructively, depending on their relative phases, which is reflected by the complex values of their respective nonlinear susceptibilities in eq 2.…”

“…The measured I SH (t) dependence was fit to the two-level model outlined above by assuming a single-exponential decay for the solvation time correlation function 2 and substituting the resulting ω eg (t) into eq 2. The pump-probe cross-correlation function (fwhm ≈ 175 fs) was measured independently using their sum frequency generation at the interface and was convoluted with eq 2 to correctly fit the initial drop.…”

“…Experimental and theoretical studies of the bulk phase solvents have shown that the solvation dynamics, which reflects dipolar relaxation of the solvent molecules in response to a charge redistribution of the solute, has a profound effect on the rates of the charge-transfer reactions. [1][2][3] Many biologically important processes occur at aqueous interfaces, e.g., the surface of cell membranes, and often involve charge transfer as one of the steps. Reactions of folded proteins, in particular enzymes, RNA, and DNA, also require consideration of the interfacial environment of these bulky molecules, for which the term "biological water" has been coined recently.…”

Theoretical Investigation of the Ground and Excited States of Coumarin 151 and Coumarin 120

“…[4][5][6][7][8] This solvatochromic behavior has allowed a number of groups to use ultrafast spectroscopic techniques to unravel the dynamics of solvation in polar solvents by examining coumarin fluorescence dynamics. 2,[9][10][11][12][13][14][15][16] Following this seminal work, researchers have begun to apply coumarin fluorescence dynamics to probe local environment fluctuations in a wide variety of chemical environments. [17][18][19][20][21][22][23][24][25][26][27][28][29] Although the energetics and dynamics of solvation for many coumarins have been well-characterized experimentally, there are still many open questions concerning the nature of the S 1 state, as well as its evolution from the Franck-Condon region following photoexcitation from the ground state.…”