Distinctive character of electronic and vibrational coherences in disordered molecular aggregates

Abstract

Coherent dynamics of coupled molecules are effectively characterized by the two-dimensional (2D) electronic coherent spectroscopy. Depending on the coupling between electronic and vibrational states, oscillating signals of purely electronic, purely vibrational or mixed character can be observed with the help of oscillation maps, constructed from the time-resolved 2D spectra. The amplitude of the beatings caused by the electronic coherence is heavily affected by the energetic disorder and consequently the electronic coherences are quickly dephased. Beatings with the vibrational character weakly depend on the disorder, assuring their long-time survival. We show that detailed modeling of 2D spectroscopy signals of molecular aggregates provides direct information on the origin of the coherent beatings.

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

“…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 .…”

“…Another mechanism allowing for long-lived electronic coherences is substantial electronic-vibrational mixing in the excited state, resulting in a vibrational coherence lifetime borrowing mechanism 47 . For this effect to be noticeable, the excitonic energy gap between the excitonic states should closely match some strong discrete vibrational mode.…”

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].…”

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].…”