posted on 2022-01-04, 20:07authored byJonathan
D. Schultz, Taeyeon Kim, James P. O’Connor, Ryan M. Young, Michael R. Wasielewski
Launching and tracking wavepacket
dynamics with two-dimensional
electronic spectroscopy (2DES) provides insight into the complex interactions
that underlie coherent processes within photoactive materials. With
the ever-growing interest in how electronic-vibrational (vibronic)
interactions direct ultrafast photophysics, methods for translating
2DES results into meaningful descriptions of the molecular potential
energy landscape must evolve correspondingly. The interpretation of
quantum beatmaps, which provide direct insight into the intra- and
interchromophoric couplings within a chemical system, frequently relies
on physical models that account for a single nuclear coordinate. However,
several recent works suggest that coupling between wavepackets borne
from several different vibrational motions affects 2DES data in meaningful
ways. We build upon these insights by directly comparing simulations
using single- and multicomponent vibronic Hamiltonians against experimental
2DES results from the organic semiconductors terrylenediimide and
ITIC, as well as the biomedical dyes methylene blue and Nile blue
A. We show that the experimental beatmaps and Fourier power spectra
are well-reproduced when both low- and high-frequency vibrational
motions are included in the simulation. Moreover, we demonstrate that
the interaction of harmonic wavepackets increases quantum beat amplitudes
in the positive-frequency rephasing signals, which significantly complicates
standard methods for separating ground- and excited-state vibrational
coherence signatures from 2DES data. These findings illustrate that
coupling between purely harmonic vibrational wavepackets can have
significant and prevalent effects on experimental 2DES results.