Quantum coherence selective 2D Raman–2D electronic spectroscopy

Abstract

Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational–vibrational, electronic–vibrational and electronic–electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment–protein complexes.

Raman and 2D electronic spectroscopies: A fruitful alliance for the investigation of ground and excited state vibrations in chlorophyll a

“…The cross-peaks at coordinates (ε, ε ± Ω), where ε in this specific case is the energy of the Qy(0,0) electronic transition, are crucial to disentangle and characterize the dynamics of the excited and ground state vibrational coherences since the two contributions are not superimposed at these coordinates [34,35]. Specific 2DES schemes, suitably designed to capture the coherent dynamics at these coordinates [30] and mixed vibrational electronic fifth-order multidimensional techniques [48], have also been proposed. Here we suggest a more straightforward procedure that does not require any modification of the 2DES setup but that just exploits the comparison between rephasing and non rephasing signal and a careful choice of the exciting spectral bandwidth to be used as spectral filter.…”

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

“…Linear vibrational techniques, such as infrared and spontaneous Raman spectroscopy, cannot monitor vibrational coherences on the excited states, whereas UV-visible absorption spectroscopy usually lacks the desired structural sensitivity. Considerable efforts have been aimed at the development of multidimensional spectroscopic techniques in order to separate the photoinduced response over additional spectral dimensions [7][8][9][10][11][12][13][14][15][16][17][18][19], which arise from the parameters tunable during the experiment, such as the time delays between multiple excitation pulses. The correlations of features on different dimensions offer a different perspective on the vibrational landscape, providing a connection between the structure of the system and its dynamics.…”

Recent advances in multidimensional ultrafast spectroscopy

“…An alternative approach by the Harel group, takes advantage of the single shot 2DES method GRAPES, called gradient-assisted multidimensional electronic-Raman spectroscopy (GAMERS) [ 187 , 188 ]. A non-resonant Raman impulsive scattering pump that generates vibrational coherences on the ground electronic state, at time t 0 , is then proceeded via a typical 2DES pulse sequence.…”