Two-dimensional electronic spectroscopy (2DES) is a method well suited to studying the ultrafast dynamics and electronic structure of molecular aggregates. In 2DES, the initial absorption frequencies of the system are correlated with the emission frequencies as a function of time between excitation and detection. The resulting 2DES spectra indicate electronic coupling and allow the dynamics of energy transfer to be extracted. Coherent and fluorescence-detected 2DES are complementary experiments that yield dramatically different spectra due to the different combinations of signal contributions produced in the two experiments. While both approaches exhibit three types of signals: ground state bleach, stimulated emission, and excited state absorption (ESA), fluorescence-detected 2DES possesses two ESA contributions with opposite signs that often cancel. In a molecular dyad system, we explore the benefits of measuring both coherent and fluorescence-detected 2DES spectra for extracting electronic structure and dynamics and discuss the implications for larger molecular aggregates such as photosynthetic systems.

Coherent versus fluorescence-detected multidimensional electronic spectroscopy of molecular systems

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ACS Fall 2022

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