Distinguishing Electronic and Vibronic Coherence in 2D Spectra by Their Temperature Dependence

Abstract

Long-lived oscillations in 2D spectra of chlorophylls are at the heart of an ongoing debate. Their physical origin is either a multipigment effect, such as excitonic coherence, or localized vibrations. We show how relative phase differences of diagonal- and cross-peak oscillations can distinguish between electronic and vibrational (vibronic) effects. While direct discrimination between the two scenarios is obscured when peaks overlap, their sensitivity to temperature provides a stronger argument. We show that vibrational (vibronic) oscillations change relative phase with temperature, while electronic oscillations are only weakly dependent. This highlights that studies of relative phase difference as a function of temperature provide a clear and easily accessible method to distinguish between vibrational and electronic coherences.

Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters

“…This effective model of the bath enables us to limit the bath description to one harmonic mode whose dynamics is treated explicitly by a master equation according to Ref. 39. In this way, the primary mode effectively provides a correct bath spectral density for the energy transfer between the carotenoid and BChl while allowing for a non-perturbative treatment.…”

Full Characterization of Vibrational Coherence in a Porphyrin Chromophore by Two-Dimensional Electronic Spectroscopy

“…A recent theoretical paper proposed that another way to differentiate vibrational from electronic coherences is to measure the relative phase (between diagonal and cross-peaks) as a function of temperature. 24 Recently a theoretical paper showed explicitly the origin of the phase dependence, as a function of excitation and detection frequencies, for a given Feynman diagram. 25 Apart from the previously discussed 0 o or 180 o degrees phase shifts observed at the maxima of the peaks on the diagonal and antidiagonal, a further phase dependence is present for frequencies detuned from the absorption maxima.…”

Resolving Vibrational from Electronic Coherences in Two-Dimensional Electronic Spectroscopy: The Role of the Laser Spectrum

“…However, electronic transitions are commonly coupled to molecular vibrational modes, and vibrational coherences both in the ground and excited states can be prepared by broadband pulses, in the same way that a coherent superposition of different excitonic or electronic states may be prepared [17]. Recent theoretical and experimental research has explored the different coherence signatures arising in 2D-ES, but for the most part possible effects from the laser spectrum have been neglected [18][19][20][21][22][23][24].…”