Multidimensional coherent spectroscopy provides insights into the vibronic structure and dynamics of complex systems. In general, the higher the dimensionality, the better the spectral discrimination and the more information that may be extracted about the system. A major impediment to widespread implementation of these methods, however, is that the acquisition time generally increases exponentially with dimensionality, prohibiting practical implementation. In this talk, we demonstrate the use of nonuniform sampling based on the projection-slice theorem and inverse Radon transform within the context of a fifth-order, 4D technique (GAMERS) designed to correlate the vibrational contributions to different electronic states. The method, in combination with gradient-assisted photon echo spectroscopy (GRAPES), reduces the acquisition time over conventional ‘point-by-point’ scanning by more than three orders of magnitude, and achieves a dynamic range exceeding 10^4.  An algorithm based on lowest-value and hybrid lowest-value projection reconstruction is presented that results in 2D Raman-like spectra with hundreds of resolvable peaks spanning the THz and fingerprint region.  This algorithm is also applied to rapid-scan 3D electronic-vibrational spectroscopy to study a variety of systems including conjugated polymers and photosynthetic pigment-protein complexes.  In the latter case, we demonstrate how modification of vibronic coupling strength can modulate energy transfer. Since increasing vibronic coupling increases internal relaxation, strongly coupled vibronic states can act as an energy funnel, which can potentially benefit energy transport.  The advent of rapid scan techniques and algorithms for processing large data sets has the potential to elevate multi-dimensional spectroscopy to that of a ubiquitous, analytical technique in the chemical, biological, and materials sciences.

High dimensionality electronic vibrational spectroscopy by projection reconstruction

ACS Fall 2021

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