Vibronic phenomena and exciton–vibrational interference in two-dimensional spectra of molecular aggregates

Abstract

A general theory of electronic excitations in aggregates of molecules coupled to intramolecular vibrations and the harmonic environment is developed for simulation of the third-order nonlinear spectroscopy signals. It is applied in studies of the time-resolved two-dimensional coherent spectra of four characteristic model systems: weakly/strongly vibronically coupled molecular dimers interacting with high/low frequency intramolecular vibrations. The results allow us to (i) classify and define the typical spectroscopic features of vibronically coupled molecules, (ii) separate the cases, when the long-lived quantum coherences due to vibrational lifetime borrowing should be expected, (iii) define when the complete exciton-vibrational mixing occurs, and (iv) when separation of excitonic and vibrational coherences is possible.

Coherence and population dynamics of chlorophyll excitations in FCP complex: Two-dimensional spectroscopy study

“…From the position of the corresponding peaks in the absorption spectrum, the frequency of such a coherence should be around 715 cm −1 or 915 cm −1 . By comparing the peak heights and assuming that the Franck-Condon factors of vibrational transitions are as small as 0.05, it could easily be deduced that the amplitude of electronic coherence should be higher than the vibrational coherence of Chl c. But the dephasing rate of the electronic coherences is known to be much shorter than the vibrational ones 48 . This would prevent the electronic coherence to be captured by the Fourier maps, except of a few cases.…”

“…Such distinction between the coherences of different origin is conveniently observed in the Fourier amplitude maps. In the rephasing spectrum, ground state coherences are manifested by strong beatings below and on the diagonal 38 while the corresponding vibronic coherences -symmetrically above the diagonal [46][47][48] . Mixed coherences, that represent superpositions of quantum mechanically mixed states, are observed as complex and asymmetric patterns of oscillating peaks in the Fourier maps 45,48 .…”

“…In the rephasing spectrum, ground state coherences are manifested by strong beatings below and on the diagonal 38 while the corresponding vibronic coherences -symmetrically above the diagonal [46][47][48] . Mixed coherences, that represent superpositions of quantum mechanically mixed states, are observed as complex and asymmetric patterns of oscillating peaks in the Fourier maps 45,48 . Electronic coherences in the rephasing spectrum manifest themselves exclusively as oscillatory cross-peaks and no oscillations on the diagonal and vice versa for the nonrephasing spectrum 38 .…”

Ultrafast energy transfer with competing channels: Non-equilibrium Förster and Modified Redfield theories

“…Despite current attention to fine effects of underdamped intramolecular vibrational modes [24][25][26][27][28] and to details of spectral density shapes [29], and despite recent efforts to introduce a paradigm shift in understanding of the origin of the photosynthetic EET efficiency [30][31][32], the overall picture of this process, as drawn by the master equations of the Förster and Redfield types, remains valid [33] (see e. g. [34] for quantitative results). Recent theoretical advances enabling exact numerical solutions of some types of energy transfer problems e.g.…”

Vibrational relaxation beyond the linear damping limit in two-dimensional optical spectra of molecular aggregates

“…Various variant of such a strategy has been simultaneously followed recently by several authors [10][11][12][13].…”