Two-dimensional electronic spectroscopy can fully characterize the population transfer in molecular systems

Area of Science:

• Physical Chemistry
• Spectroscopy
• Chemical Dynamics

Background:

• Excitation energy transfer in complex systems involves intermediate states, requiring identification of spectral signatures and transfer schemes.
• Transient absorption spectroscopy often yields ambiguous results for decomposition and characterization of these schemes.
• Absorptive 2D spectra offer a more intuitive representation resembling population transfer matrices, suggesting potential for unambiguous decomposition.

Purpose of the Study:

• To demonstrate that the combination of absorptive 2D and linear absorption spectra contains all necessary information for unambiguous analysis of energy transfer.
• To develop a model for analyzing absorptive 2D spectra and extracting physical parameters.
• To enable the decomposition of 2D spectra into stimulated emission, ground-state bleach, and excited-state absorption components.

Main Methods:

• Development of a model for a broad class of absorptive 2D spectra.
• Analytical proof of unique inversion of 2D spectra to physical parameters.
• Numerical inversion by fitting experimental 2D and absorption spectra using a matrix formulation suitable for fast computation.

Main Results:

• The combined absorptive 2D and linear absorption spectra uniquely determine species-associated spectra and intrinsic rate constants.
• The matrix formulation facilitates efficient numerical inversion for data analysis.
• The method allows for near-unambiguous decomposition of 2D spectra into their constituent components (stimulated emission, ground-state bleach, excited-state absorption).

Conclusions:

• The presented method provides a robust and unambiguous approach to characterizing energy transfer dynamics in complex systems.
• Combining absorptive 2D and linear absorption spectroscopy overcomes the ambiguity issues inherent in transient absorption spectroscopy.
• The developed model and numerical procedure are applicable for efficient analysis of experimental spectroscopic data.