Resonance Raman analysis of nonlinear solvent dynamics: Betaine-30 in ethanol

Tryptophan is widely used as an intrinsic fluorophore for studies of protein structure and dynamics. Its fluorescence is known to have two decay components with lifetimes of 0.5 and 3.1 ns. In this work we measure the ultrafast dynamics of Tryptophan at <100 fs through measurements and modeling of the Raman excitation profiles with time-dependent wave packet propagation theory. We use a Brownian oscillator model to simulate the water-tryptophan interaction. Upon photoexcitation to the higher singlet electronic state (B b ) the structure of tryptophan is distorted to an overall expansion of the pyrrole and benzene rings. The total reorganization energy for Trp in water is estimated to be 2169 cm À1 with a 1230 cm À1 contribution from the inertial response of water. The value of reorganization energy of water corresponding to the fast response is found to be higher than that obtained upon excitation to the L a state by previous studies that used computational simulations. The longtime dynamics of Trp manifests as a conformational heterogeneity at shorter times and contributes to inhomogeneous broadening of the Raman profiles (315 cm À1 ).

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“…Using the overdamped Brownian oscillator model (33,34,40,41), the following expressions were obtained as g solv ðtÞ ¼ g 0 ðtÞ þ i g 00 ðtÞ;…”

Section: Solvent-dephasing Functionmentioning

confidence: 99%

Mode-Specific Reorganization Energies and Ultrafast Solvation Dynamics of Tryptophan from Raman Line-Shape Analysis

Milán‐Garcés

Kaptan

Puranik

2013

Biophysical Journal

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“…Ultrafast transient absorption measurements in different solvents were used to estimate values for reorganization energies by considering the effects of low and high frequency vibrational motions, but these electronic measurements cannot identify the contribution of specific vibrational modes to the total reorganization energy. 7,17 Resonance Raman intensity analysis has been used to probe initial Franck-Condon dynamics including solvent isotope effects, suggesting that methyl group motions play a larger role than hydroxyl group motion in the dephasing of the electronic state. 18,19 Picosecond timeresolved Raman spectroscopy was used to follow cooling and intramolecular vibrational redistribution on the electronic ground state following the back electron transfer reaction, but unfortunately the time resolution was insufficient to directly monitor structural changes on the electronic excited state.…”

Section: Introductionmentioning

confidence: 99%

Excited state structural evolution during charge-transfer reactions in betaine-30

Silva

Frontiera

2016

Phys. Chem. Chem. Phys.

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Ultrafast photo-induced charge-transfer reactions are fundamental to a number of photovoltaic and photocatalytic devices, yet the multidimensional nature of the reaction coordinate makes these processes difficult to model theoretically. Here we use femtosecond stimulated Raman spectroscopy to probe experimentally the structural changes occurring following photoexcitation in betaine-30, a canonical intramolecular charge-transfer complex. We observe changes in vibrational mode frequencies and amplitudes on the femtosecond timescale, which for some modes results in frequency shifts of over 20 cm(-1) during the first 200 fs following photoexcitation. These rapid mode-specific frequency changes track the planarization of the molecule on the 400 ± 100 fs timescale. Oscillatory amplitude modulations of the observed high frequency Raman modes indicate coupling between specific high frequency and low frequency vibrational motions, which we quantify for 6 low frequency modes and 4 high frequency modes. Analysis of the mode-specific kinetics is suggestive of the existence of a newly discovered electronic state involved in a relaxation pathway, which may be a low-lying triplet state. These results directly track the multiple nuclear coordinates involved in betaine-30's reactive pathway, and should be of use in rationally designing molecular systems with rapid electron transfer processes.

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“…1,[4][5][6] Linear-response theory requires that S V ͑t͒, the subsequent relaxation of the solute-solvent potential energy V as the solvent adapts to the solute's new appearance, has to be the same as C VV ͑t͒, the equilibrium potential energy fluctuations one would see with an electronically-excitedstate solute. [17][18][19][20][21] It is not uncommon to find solvation-dynamics examples in the literature which refer to any deviations from this expectation as linear-response failures. However, even in these examples, linearresponse theory tends to be remarkably quantitative.…”

Section: Introductionmentioning

confidence: 99%

The molecular origins of nonlinear response in solute energy relaxation: The example of high-energy rotational relaxation

Tao

Stratt

2006

The Journal of Chemical Physics

103

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A key step in solution-phase chemical reactions is often the removal of excess internal energy from the product. Yet, the way one typically studies this process is to follow the relaxation of a solute that has been excited into some distribution of excited states quite different from that produced by any reaction of interest. That the effects of these different excitations can frequently be ignored is a consequence of the near universality of linear-response behavior, the idea that relaxation dynamics is determined by the solvent fluctuations (which may not be all that different for different kinds of solute excitation). Nonetheless, there are some clear examples of linear-response breakdowns seen in solute relaxation, including a recent theoretical and experimental study of rapidly rotating diatomics in liquids. In this paper we use this rotational relaxation example to carry out a theoretical exploration of the conditions that lead to linear-response failure. Some features common to all of the linear-response breakdowns studied to date, including our example, are that the initial solute preparation is far from equilibrium, that the subsequent relaxation promotes a significant rearrangement of the liquid structure, and that the nonequilibrium response is nonstationary. However, we show that none of these phenomena is enough to guarantee a nonlinear response. One also needs a sufficient separation between the solute time scale and that of the solvent geometry evolution. We illustrate these points by demonstrating precisely how our relaxation rate is tied to our liquid-structural evolution, how we can quantitatively account for the initial nonstationarity of our effective rotational friction, and how one can tune our rotational relaxation into and out of linear response.

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Resonance Raman analysis of nonlinear solvent dynamics: Betaine-30 in ethanol

Cited by 24 publications

References 31 publications

Mode-Specific Reorganization Energies and Ultrafast Solvation Dynamics of Tryptophan from Raman Line-Shape Analysis

Mode-Specific Reorganization Energies and Ultrafast Solvation Dynamics of Tryptophan from Raman Line-Shape Analysis

Excited state structural evolution during charge-transfer reactions in betaine-30

The molecular origins of nonlinear response in solute energy relaxation: The example of high-energy rotational relaxation

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