Revealing Intermolecular Electronic and Vibronic Coherence with Polarization-Dependent Two-Dimensional Beating Maps

Abstract

Two-dimensional electronic spectroscopy (2DES) has been widely employed as an efficient tool to reveal the impact of intermolecular electronic and/ or vibronic quantum coherence on excitation energy transfer in light-harvesting complexes. However, intramolecular vibrational coherence would also contribute to oscillating signals in 2D spectra, along with the intermolecular coherence signals that are directly related to energy transfer. In this work, the possibility of screening the vibrational coherence signals is explored through polarization-dependent 2DES. The all-parallel (AP) and double-crossed (DC) polarization-dependent two-dimensional rephasing spectra (2DRS) are simulated for a minimalist heterodimer model with vibrational coupling. By combining the DC-2DRS and the 2D beating maps, we demonstrate that the population and vibrational coherence signals can be largely suppressed, resulting in highlighted intermolecular electronic and vibronic coherence signals. Moreover, the AP-and DC-2DBMs show rather different patterns at the vibrational frequency, indicating a possible way to identify pure vibrational coherence.

Simulation of the Pump–Probe Spectra and Excitation Energy Relaxation of the B850 Band of the LH2 Complex in Purple Bacteria

“…As stated above, we incorporate the static disorder over site energies into the HEOM, and use the following scheme for averaging over different (random) orientations of the LH2 complex. The relation between the orientationally averaged third order response function and the molecular frame response functions is given by , false⟨ R total ⟩ ori = false ∑ m 1 m 2 m 3 m 4 C m 1 m 2 m 3 m 4 R m ⃗ 1 m ⃗ 2 m ⃗ 3 m ⃗ 4 mol where m⃗ k are the molecular axes m⃗ k ∈ { x⃗ , y⃗ , z⃗ } in the molecular frame. The transformation coefficients C m 1 m 2 m 3 m 4 take the form of C m 1 m 2 m 3 m 4 = 1 15 false( δ m 1 m 2 δ m 3 m 4 + δ m 1 m 3 δ m 2 m 4 + δ m 1 m 4 δ m 2 m 3 false) For convenience, all the 21 nonzero coefficients are listed in Table .…”