Coherent wavepacket motion in an ultrafast electron transfer system monitored by femtosecond degenerate four-wave-mixing and pump–probe spectroscopy

Nagasawa, Yutaka; Yoneda, Yusuke; Nambu, Shohei; Muramatsu, Masayasu; Takeuchi, Eisuke; Tsumori, Hiroki; Morikawa, Soichiro; Katayama, Tetsuro; Miyasaka, Hiroshi

doi:10.1016/j.chemphys.2014.02.004

Cited by 11 publications

(11 citation statements)

References 37 publications

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“…Upon excitation, the electron density is removed from the bonds of the conjugated π-system, effectively weakening the classical “spring constant” and lowering the energy of the vibrational modes in the excited state. As a result, the Raman spectrum of the excited state is red-shifted compared to the ground-state Raman spectrum, an effect which has been reported previously in a similar system, oxazine 1 . The Raman spectrum extracted from the resonant pump data indicates that the coherence originates from an excited-state wavepacket and agrees with the position of the phase-flips at λ max *abs and λ max fl .…”

Section: Resultssupporting

confidence: 84%

Spectral Signatures of Ground- and Excited-State Wavepacket Interference after Impulsive Excitation

2020

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Impulsive transient absorption spectroscopy is used to track the formation and evolution of vibrational coherences in cresyl violet perchlorate under different excitation conditions. Resonant and off-resonant pump pulses result in the selective formation of excited (S 1 )-and ground (S 0 )-state wavepackets. Partially resonant and broadband excitation conditions lead to the simultaneous formation of wavepackets in the ground and excited states. The wavepackets are characterized by the phase-flips in the coherent signal associated with wavepacket motion across the absorption and emission maxima and by a red shift of 2−10 cm −1 in the Raman features of the excited state compared to the groundstate wavepacket. We observe that, when wavepackets are simultaneously excited on the ground-and excited-state surfaces, interference on a picosecond timescale between coherent oscillations in the two wavepackets gives rise to features that cannot be attributed to the passage of a wavepacket through a conical intersection, such as shifting phase-flips and zero-amplitude nodes. Wavepacket filtering using windowed Fourier transforms highlights these interference effects and demonstrates that special care must be taken in order to properly interpret data that have been processed in this manner.

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Section: Resultssupporting

confidence: 84%

Spectral Signatures of Ground- and Excited-State Wavepacket Interference after Impulsive Excitation

2020

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“…In the Ox1/DMA system, the observation of persistent oscillatory features in pump-probe measurements spurred debates on whether PET involved the coherent transfer of an electron and to what extent this was mediated by molecular vibrations and solvent interactions. − While PET remains a poor fit for the cresyl violet and tetrazine system, the excitation dependence of the new ESA peak at 425 THzlocated only at excitations above 550 THzsuggests that molecular vibrations and solvent mediation play an important role, pointing to ESPT as a possible mechanistic pathway for the fluorescence quenching. In the cresyl violet and tetrazine system, the two exocyclic amine/iminium groups of cresyl violet can act as weak photoacids, while tetrazine can be considered a weak photobase that mediates ESPT to the solvent.…”

Section: Resultsmentioning

confidence: 99%

Resolving the Fluorescence Quenching Mechanism of an Oxazine Dye Using Ultrabroadband Two-Dimensional Electronic Spectroscopy

et al. 2019

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The design and optimization of fluorescent labels and fluorogenic probes rely heavily on their ability to distinguish among multiple competing fluorescence quenching mechanisms. Cresyl violet, a member of the 1,4-oxazine family of dyes, has generally been regarded as an exemplary fluorescent probe; however, recent ultrafast experiments revealed an excited-state decay kinetic of 1.2 ps, suggesting the presence of a transient photochemical state. Here, we present ultrabroadband two-dimensional electronic spectroscopy (2D ES) measurements of cresyl violet in the presence of the fluorescence quenching agent 3,6-di(2-hydroxyethyl)-1,2,4,5-tetrazine. The broad spectral bandwidth allows for the evaluation of multiple fluorescence quenching mechanisms such as exciton formation, photoinduced electron transfer, resonance energy transfer, and excited-state proton transfer. The 2D electronic spectra in the presence and absence of the quencher suggest that excited-state proton transfer drives the system’s excited-state dynamics and leads to a cresyl violet tautomer involved in fluorescence quenching. The invocation of the tautomeric form of cresyl violet neatly resolves longstanding inconsistencies in the photophysics of oxazine dyes more generally. Although still under development, the application of ultrabroadband 2D ES to a molecular system represents a compelling demonstration of the technique’s future role in the study of photochemical reaction mechanisms.

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“…On the contrary, Bixon and Jortner modeled the coherence effects in nonadiabatic ET and proposed that the observed oscillations in a charge transfer complex are not vibrationally coherent product formation, rather it comes from the initial state . Various experiments were further conducted including transient IR, stimulated Raman, and 2D spectroscopies, ,, in addition to pump–probe measurement in the visible range. ,− , A recent femtosecond X-ray scattering study suggested that the coherent translational motions of a solvent mediate the ultrafast intramolecular ET in a mixed-valence bimetallic complex through hydrogen bonding between a solvent and solute . However, it is still challenging to distinguish which vibrations are coupled to a reaction and which ones are merely “spectator modes”, because the number of Franck–Condon active vibrations observed by ultrafast spectroscopy is usually quite large, encompassing the absorbers Raman-active modes .…”

Section: Introductionmentioning

confidence: 99%

Vibrational Dephasing along the Reaction Coordinate of an Electron Transfer Reaction

et al. 2021

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The role of molecular vibration in photoinduced electron transfer (ET) reactions has been extensively debated in recent years. In this study, we investigated vibrational wavepacket dynamics in a model ET system consisting of an organic dye molecule as an electron acceptor dissolved in various electron donating solvents. By using broad band pump−probe (BBPP) spectroscopy with visible laser pulses of sub-10 fs duration, coherent vibrational wavepackets of naphthacene dye with frequencies spanning 170−1600 cm −1 were observed in the time domain. The coherence properties of 11 vibrational modes were analyzed by an inverse Fourier filtering procedure, and we discovered that the dephasing times of some vibrational coherences are reduced with increasing ET rates. Density functional theory calculations indicated that the corresponding vibrational modes have a large Huang−Rhys factor between the reactant and the product states, supporting the hypothesis that the loss of phase coherence along certain vibrational modes elucidates that those vibrations are coupled to the reaction coordinate of an ET reaction.

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Coherent wavepacket motion in an ultrafast electron transfer system monitored by femtosecond degenerate four-wave-mixing and pump–probe spectroscopy

Cited by 11 publications

References 37 publications

Spectral Signatures of Ground- and Excited-State Wavepacket Interference after Impulsive Excitation

Spectral Signatures of Ground- and Excited-State Wavepacket Interference after Impulsive Excitation

Resolving the Fluorescence Quenching Mechanism of an Oxazine Dye Using Ultrabroadband Two-Dimensional Electronic Spectroscopy

Vibrational Dephasing along the Reaction Coordinate of an Electron Transfer Reaction

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