Observation of Ultrafast Coherence Transfer and Degenerate States with Polarization-Controlled Two-Dimensional Electronic Spectroscopy

Abstract

Optical spectroscopy is a powerful tool to interrogate quantum states of matter. We present simulation results for the cross-polarized two-dimensional electronic spectra of the light-harvesting system LH2 of purple bacteria. We identify a spectral feature on the diagonal, which we assign to ultrafast coherence transfer between degenerate states. The implication for the interpretation of previous experiments on different systems and the potential use of this feature are discussed. In particular, we foresee that this kind of feature will be useful for identifying mixed degenerate states and for identifying the origin of symmetry breaking disorder in systems like LH2. Furthermore, this may help identify both vibrational and electronic states in biological systems such as proteins and solid-state materials such as hybrid perovskites.

Lessons from combined experimental and theoretical examination of the FTIR and 2D-IR spectroelectrochemistry of the amide I region of cytochrome c

“…which have been used in the literature assignments and which are defined by the residue numbers in Table S2 in the Supplementary material. This was achieved by insertion of a segment projection operator in the response function 50 governing the FTIR signal (Eq. 2 in Supplementary material), that is weighting the contribution of each eigenstate to the segment spectrum by the population of the eigenstate on that specific segment.…”

Computational spectroscopy of complex systems

“…148,209,210 For coupled systems, exciton dynamics may lead to an additional decay of the anisotropy. 31,46,211,212 Such population dynamics can be analyzed through the population transfer between different sites P nl (t) = ⟨U nl (t, 0)⟩, where analysis of different initial, l, and final states, n, can provide useful insight. The nature of the population transfer in biological systems has been debated, 213,214 and analysis of the population dynamics in photosynthetic systems has been widely studied computationally.…”

“…A number of these spectra were already provided in Ref. 31, where a detailed description of the simulation parameters is also provided. In short, the couplings between different bacteriochlorophyll a molecules were determined using the 1kzu protein databank structure 240 using the transition-dipole coupling model.…”

“…( 6)] for each molecule with the parameters adjusted to reproduce the linear absorption spectra. 31 The used structure is shown in Fig. 6 next to the simulated linear absorption, linear dichroism, and fluorescence spectra.…”

“…Therefore, special techniques have been developed to predict excited state solvent shifts 26,27 of molecules in the condensed phase and couplings 28,29 between those at a speed sufficient enough to be used in quantum-classical response function based spectral calculations. 30,31 Such calculations provide the possibility of predicting and interpreting advanced spectroscopies as two-dimensional (2D) infrared 32 and electronic spectroscopies 33 of complex systems containing tens or even hundreds of chromophores. 34,35 This kind of computational spectroscopy of complex systems is needed for the interpretation of experimental spectra, design of new materials, and prediction of spectral properties.…”