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.
Highlights
Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging
In gradient-assisted multidimensional electronic Raman spectroscopy (GAMERS), an additional pulse serves to excite the sample into a non-equilibrium state before being interrogated by the GRadient-Assisted Photon Echo Spectroscopy (GRAPES) pulse sequence
The single-quantum coherence (SQC) represents a superposition of electronic states, while the zero-quantum coherence (ZQC) represents a wave packet within either the ground or excited electronic state manifolds
Summary
Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. The vibronic structure of the system is 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. We present an approach that provides direct correlation between impulsively driven low-frequency modes such as phonons, vibrations and (multi-)excitons with quantum coherence selectivity through control of resonance This six-wave mixing (6WM) Raman–electronic spectroscopy produces a fully coherent 4D correlation spectrum between select ground and excited state vibrations and ground and excited state electronic transitions. Among the many unexplored physical phenomena accessible by this technique, we demonstrate the ability to isolate signals from—and assign signals to—distinct vibronic pathways and to spectroscopically distinguish ground and excited state vibrational coherences We call this method gradient-assisted multidimensional electronic Raman spectroscopy (GAMERS). We show that GAMERS directly measures the coupling of low-frequency vibrational modes to one another as well as to higher-frequency electronic transitions in an organic dye in dilute solution
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