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In recent years, action-detected ultrafast spectroscopies have gained popularity offering distinct advantages over their coherently-detected counterparts, such as spatially-resolved and operando measurements with high sensitivity. However, there are also fundamental limitations connected to the process of signal generation in action-detected experiments. Here we perform fluorescence- detected two-dimensional electronic spectroscopy (F-2DES) of the light-harvesting II (LH2) complex from purple bacteria. We demonstrate that the B800-B850 energy transfer process in LH2 is weak but observable in F-2DES, unlike in coherently-detected 2DES where the energy transfer is visible with 100% contrast. We explain the weak signatures using a disordered excitonic model that accounts for experimental conditions. We further derive a general formula for the presence of excited-state signals in multichromophoric aggregates, dependent on the aggregate geometry, size, excitonic coupling and disorder. We find that the prominence of excited-state dynamics in action- detected spectroscopy offers a unique probe of excitonic delocalization in multichromophoric systems.
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Observation of Ultrafast Coherence Transfer and Degenerate States with Polarization-Controlled Two-Dimensional Electronic Spectroscopy
Optical spectroscopy is a powerful tool to inter- 7 rogate quantum states of matter. We present simulation results for 8 the cross-polarized two-dimensional electronic spectra of the light- 9 harvesting system LH2 of purple bacteria. We identify a spectral feature on the diagonal, which we assign to ultrafast coherence transfer between degenerate states. The implication for the interpretation of previous experiments on different systems and the potential use of this feature are discussed. In particular, we foresee that this kind of feature will be useful for identifying mixed degenerate states and for identifying the origin of symmetry breaking disorder in systems like LH2. Furthermore, this may help identify both vibrational and electronic states in biological systems such as proteins and solid-state materials such as hybrid perovskites.
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- Award ID(s):
- 1914608
- PAR ID:
- 10198035
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry B
- ISSN:
- 1520-6106
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpcb.0c08126
