Broad-Band Pump–Probe Spectroscopy Quantifies Ultrafast Solvation Dynamics of Proteins and Molecules

Abstract

In this work, we demonstrate the use of broad-band pump-probe spectroscopy to measure femtosecond solvation dynamics. We report studies of a rhodamine dye in methanol and cryptophyte algae light-harvesting proteins in aqueous suspension. Broad-band impulsive excitation generates a vibrational wavepacket that oscillates on the excited-state potential energy surface, destructively interfering with itself at the minimum of the surface. This destructive interference gives rise to a node at a certain probe wavelength that varies with time. This reveals the Gibbs free-energy changes of the excited-state potential energy surface, which equates to the solvation time correlation function. This method captures the inertial solvent response of water (∼40 fs) and the bimodal inertial response of methanol (∼40 and ∼150 fs) and reveals how protein-buried chromophores are sensitive to the solvent dynamics inside and outside of the protein environment.

Ultrafast Solvation Dynamics and Vibrational Coherences of Halogenated Boron-Dipyrromethene Derivatives Revealed through Two-Dimensional Electronic Spectroscopy

“…Our results are consistent with previous measurements where an ultrafast component of ~100 fs or less was observed and attributed to the inertial component of the solvent response of methanol, and a longer timescale component of a few picoseconds was observed and attributed to the diffusive component of the solvent response. 42, 43, 46, 82, 86–94 In our studies performed on BODIPY chromophores in methanol, we observe an ultrafast relaxation of 57 fs for BODIPY-2I and 59 fs for BODIPY-2H and attribute this ultrafast component to an inertial solvent response – consistent with previous studies. 42, 43, 46, 82, 86–94 The longer timescale component of ~2 ps for BODIPY-2H and ~1 ps for BODIPY-2I is attributed to the diffusive solvent response.…”

“…48, 49, 50–57 More recently, pump-probe spectroscopy has been used to obtain ν(t), and extract timescales associated with the relaxation of electronic excited states through monitoring the time-dependent frequency change in the node resulting from excited state wavepackets in the stimulated emission. 81–82 Though the projection of the 2DES spectra onto the λ 3 axis is equivalent to the pump-probe spectra, due to the limited spectral bandwidth of the incoming pulses this analysis cannot be applied to the current data as distinct transitions arising from the ground state bleach and stimulated emission are not resolved. However, information regarding the relaxation of the BODIPY S 1 state can still be extracted from the 2DES spectra through analyzing spectral lineshape changes of the λ 3 projection.…”

Carotenoid-to-bacteriochlorophyll energy transfer through vibronic coupling in LH2 from Phaeosprillum molischianum

“…6 c. For both modes, we observe two amplitude maxima: one approaching the S 2 absorption maximum and one red-shifted by the vibrational frequency relative to a zero-phonon line estimated to be near 18.400 cm −1 (see SI). This is exactly the amplitude pattern expected from consideration of ground-state coherent pathways (i.e., impulsive stimulated Raman scattering) in this system (Lincoln et al 2016 ; Jumper et al 2016 ). The crucial observation for interpretation of the physical significance of these modes, beyond them being simple ground-state vibrations, is the overlap between the lower-energy amplitude maximum of the 1465 cm −1 mode and the Q x B850 band.…”

Early Time Solvation Dynamics Probed by Spectrally Resolved Degenerate Pump‐Probe Spectroscopy

“…Thus, using spectrally‐resolved pump‐probe technique, one can also envisage the idea of directly monitoring the time‐dependent gain in stimulated emission spectrum obviating the need of spectral reconstruction and estimation of time‐zero spectrum in non‐polar solvent, which we present in this work. It is worthy to mention here that spectrally‐resolved pump‐probe spectroscopy has been used to study synergistic behaviour in binary solvent mixtures and vibrational wavepacket interferometery measuring solvation in methanol and in proteins; two dimensional electronic spectroscopy has also been used to study solvation . Fluorescence correlation spectroscopy and time‐dependent Stokes shift was also implemented to study solvation dynamics in membranes .…”