Multidimensional Vibrational Coherence Spectroscopy

Abstract

Multidimensional vibrational coherence spectroscopy has been part of laser spectroscopy since the 1990s and its role in several areas of science has continuously been increasing. In this contribution, after introducing the principals of vibrational coherence spectroscopy (VCS), we review the three most widespread experimental methods for multidimensional VCS (multi-VCS), namely femtosecond stimulated Raman spectroscopy, pump-impulsive vibrational spectroscopy, and pump-degenerate four wave-mixing. Focus is given to the generation and typical analysis of the respective signals in the time and spectral domains. Critical aspects of all multidimensional techniques are the challenges in the data interpretation due to the existence of several possible contributions to the observed signals or to optical interferences and how to overcome the corresponding difficulties by exploiting experimental parameters including higher-order nonlinear effects. We overview how multidimensional vibrational coherence spectroscopy can assist a chemist in understanding how molecular structural changes and eventually photochemical reactions take place. In order to illustrate the application of the techniques described in this chapter, two molecular systems are discussed in more detail in regard to the vibrational dynamics in the electronic excited states: (1) carotenoids as a non-reactive system and (2) stilbene derivatives as a reactive system.

Tracking Structural Evolution during Symmetry‐Breaking Charge Separation in Quadrupolar Perylene Bisimide with Time‐Resolved Impulsive Stimulated Raman Spectroscopy

“…But this technique offers limited observable frequency window (>1000 cm −1 ) and time resolution (>200 fs) owing to the intrinsic characteristics of mid‐IR probe pulses. As complementary tools, various multidimensional time‐resolved Raman spectroscopy methods, which have distinct advantages of mode‐specific resonance enhancement and the capability of measuring full vibrational spectra from terahertz to 3000 cm −1 , have been also exploited . Among them, femtosecond stimulated Raman spectroscopy (FSRS), a frequency‐domain Raman technique, has provided valuable insights into structural changes during the inter/intramolecular CT processes .…”

“…As complementary tools, various multidimensional time‐resolved Raman spectroscopy methods, which have distinct advantages of mode‐specific resonance enhancement and the capability of measuring full vibrational spectra from terahertz to 3000 cm −1 , have been also exploited . Among them, femtosecond stimulated Raman spectroscopy (FSRS), a frequency‐domain Raman technique, has provided valuable insights into structural changes during the inter/intramolecular CT processes . However, under resonance conditions, some vibrational modes in the excited‐state Raman spectra exhibit dispersive lineshapes over nontrivial backgrounds, which makes it difficult to analyze the data accurately.…”

“…However, under resonance conditions, some vibrational modes in the excited‐state Raman spectra exhibit dispersive lineshapes over nontrivial backgrounds, which makes it difficult to analyze the data accurately. This issue can be surmounted by using time‐domain Raman techniques, for example, time‐resolved impulsive stimulated Raman spectroscopy (TR‐ISRS, which is also called as pump impulsive vibrational spectroscopy (Pump‐IVS)) and pump degenerate four‐wave‐mixing (Pump‐DFWM) . The two main experimental barriers of the time‐domain Raman methods for recording full vibrational manifolds in the excited state were 1) generation of a highly stable ultrashort (sub‐10‐fs) Raman pump pulse creating vibrational coherence (VC) in the excited state and 2) disentanglement of excited‐state VC signals from large contributions of ground‐state molecules and solvents.…”

Two-Dimensional Impulsively Stimulated Resonant Raman Spectroscopy of Molecular Excited States

“…Coherent multidimensional Raman spectroscopy is well suited to directly address excited-state vibrational properties in time and frequency domains due to its "fingerprint" specificity over the full vibrational manifold of interest [20][21][22][23][24]. Furthermore, Raman spectroscopy benefits from resonance enhancements of specific chromophore signatures and thereby provides a route to comprehensively investigate vibrational energy flow during reactive transformations by selectively probing specific environments [25].…”

Sub-picosecond C=C bond photo-isomerization: evidence for the role of excited state mixing

“…The vibrational spectra of both AT and 13C isomers in ASR both in the ground and excited states were analysed in detail [91]. The experimental techniques used rely on degenerate fourwave-mixing (DFWM) and impulsive vibrational spectroscopy (IVS), which can be performed also in the excited state, due to the action of an actinic pump pulse as a function of delay time [107][108][109][110].…”