Femtosecond Stimulated Raman Spectroscopy of Flavin after Optical Excitation

Abstract

In blue-light photoreceptors using flavin (BLUF), the signaling state is formed already within several 100 ps after illumination, with only small changes of the absorption spectrum. The accompanying structural evolution can, in principle, be monitored by femtosecond stimulated Raman spectroscopy (FSRS). The method is used here to characterize the excited-state properties of riboflavin and flavin adenine dinucleotide in polar solvents. Raman modes are observed in the range 90-1800 cm(-1) for the electronic ground state S(0) and upon excitation to the S(1) state, and modes >1000 cm(-1) of both states are assigned with the help of quantum-chemical calculations. Line shapes are shown to depend sensitively on resonance conditions. They are affected by wavepacket motion in any of the participating electronic states, resulting in complex amplitude modulation of the stimulated Raman spectra. Wavepackets in S(1) can be marked, and thus isolated, by stimulated-emission pumping with the picosecond Raman pulses. Excited-state absorption spectra are obtained from a quantitative comparison of broadband transient fluorescence and absorption. In this way, the resonance conditions for FSRS are determined. Early differences of the emission spectrum depend on excess vibrational energy, and solvation is seen as dynamic Stokes shift of the emission band. The nπ* state is evidenced only through changes of emission oscillator strength during solvation. S(1) quenching by adenine is seen with all methods in terms of dynamics, not by spectral intermediates.

Direct observation of subpicosecond vibrational dynamics in photoexcited myoglobin

“…1 do not differ by the Raman spectrum only 46 . The most simple correction is possible by fitting the baseline with a spline 47 and dividing it from the spectrum [48][49][50] . In our case the spline is applied with variable values of interpolant, and limited to wavelength regions not involved in the FSRRS effects (see Supplementary Fig.…”

Bimodal Exciplex Formation in Bimolecular Photoinduced Electron Transfer Revealed by Ultrafast Time-Resolved Infrared Absorption

“…[52][53][54][55][56][57] We have recently demonstrated how time-resolved infrared (TRIR) spectroscopy can be advantageously used to distinguish different intermediates involved in bimolecular photoinduced CS processes when no significant difference can be detected in the visible region. [58][59][60] Tight ion pairs generated upon static quenching 61 and loose ion pairs formed by dynamic quenching could be spectrally differentiated using the methylperylene/tetracyanoethylene (MePe/TCNE) D/A pair.…”

Femtosecond stimulated Raman spectroscopy by six-wave mixing

“…[1][2][3][4][5][6][7][8][9][10][11][12] Recent applications have revealed new insights into systems ranging from proteins 9,10,12 to organic photovoltaic materials. 4,11 The FSRS technique is essentially a sequence of two events: (i) an electronically resonant (actinic) pump pulse initiates a photochemical process; (ii) a stimulated Raman spectrum is obtained at various delay times using a combination of narrowband and broadband laser pulses.…”