Origin of Unexpectedly Simple Oscillatory Responses in the Excited-State Dynamics of Disordered Molecular Aggregates

Abstract

Unraveling the many facets of coherent and incoherent exciton motion in an ensemble of chromophores is an inherently complex quantum mechanical problem that has triggered a vivid debate on the role of quantum eects in molecular materials and biophysical systems. Here the dynamics of a statistical ensemble of molecular aggregates consisting of identical chromophores is investigated within a new theoretical framework.

Electronic coherence lifetimes of the Fenna–Matthews–Olson complex and light harvesting complex II

“…, where N is the number of chromophores and J is the inter-site electronic coupling strength. 16 Comparison to their predicted value of 53 fs of the electronic coherence lifetime of FMO, we nd good agreement. However for LH2, which has more chromophores and higher coupling strength (at least in the B850 band), we should expect the coherence lifetime to be even shorter.…”

“…The "population time", T, contains both population dynamics and the coherences between states within the excited or ground state manifold, which are the focus of this study and are detected as oscillations of the signal as a function of T. A recent theoretical study by Gelin et al clearly partitions how electronic and vibrational degrees-of-freedom contribute to coherences at different timescales. 16 At a <100 fs timescale, the time evolution is independent of nuclear degrees-of-freedom and is exclusively determined by electronic coupling. On a longer timescale, delocalized vibrations coupled electronic states form "vibronic" coherences, which eventually turn into purely vibrational coherences aer a critical time s D y 2p/s, where s is the dispersion of the static disorder.…”

Time-dependent density matrix renormalization group quantum dynamics for realistic chemical systems

“…TDVP methods were also applied by Borrelli and coworkers to study electron-transfer problems in realistic models comprising more than 200 nuclear vibrations coupled to the electronic states 41 and the coherences in a model excitonic system 42 . In 2018, some of us implemented a unitary transformation approach for realistic vibronic Hamiltonians and simulated the charge transfer dynamics and 2D electronic spectrum of the oligothiophene/fullerene interface in organic solar cells via TEBD methods.…”

Hierarchical Equations-of-Motion Method for Momentum System–Bath Coupling

“…Let us now introduce the new coordinates, the center-of-mass coordinate ( is the total mass) and the relative distance coordinates The coordinate transformation of eqs 2 and 3 is linear, but not canonical, while the determinant of the transformation matrix equals one. 39 − 41 The original momenta P k are connected to the new momenta P ≡– iℏd / dQ and p k ≡– iℏd / dq k as follows: In these new variables where ( p 0 ≡ p N ≡ 0). The first term in eq 5 describes the center-of-mass motion of the chain, which is totally decoupled from the internal dynamics of the chain specified by the Hamiltonian H .…”