Distinctive character of electronic and vibrational coherences in disordered molecular aggregates

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 origin can be observed. Even in the "mixed" molecular systems two types of coherent beats having either electronic or vibrational character can be distinguished by analyzing oscillation Fourier maps, constructed from time-resolved 2D spectra. The amplitude of the beatings with the electronic character is heavily affected by the energetic disorder and consequently electronic coherences are quickly dephased. Beatings with the vibrational character depend weakly on the disorder, assuring their long-time survival. We show that detailed modeling of 2D spectroscopy signals of molecular aggregates providesdirect information on the origin of the coherent beatings.Comment: 7 pages, 4 figures, 1 tabl

Probing environment fluctuations by two-dimensional electronic spectroscopy of molecular systems at temperatures below 5 K

Citation: Rancova, O., Jankowiak, R., & Abramavicius, D. (2015). Probing environment fluctuations by two-dimensional electronic spectroscopy of molecular systems at temperatures below 5 K. Journal of Chemical Physics, 142(21), 18. doi:10.1063/1.4918584Two-dimensional (2D) electronic spectroscopy at cryogenic and room temperatures reveals excitation energy relaxation and transport, as well as vibrational dynamics, in molecular systems. These phenomena are related to the spectral densities of nuclear degrees of freedom, which are directly accessible by means of hole burning and fluorescence line narrowing approaches at low temperatures (few K). The 2D spectroscopy, in principle, should reveal more details about the fluctuating environment than the 1D approaches due to peak extension into extra dimension. By studying the spectral line shapes of a dimeric aggregate at low temperature, we demonstrate that 2D spectra have the potential to reveal the fluctuation spectral densities for different electronic states, the interstate correlation of static disorder and, finally, the time scales of spectral diffusion with high resolution. (C) 2015 AIP Publishing LLC

Advancing hierarchical equations of motion for efficient evaluation of coherent two-dimensional spectroscopy

To advance hierarchial equations of motion as a standard theory for quantum dissipative dynamics, we put forward a mixed Heisenberg--Schrodinger scheme with block-matrix implementation on efficient evaluation of nonlinear optical response function. The new approach is also integrated with optimized hierarchical theory and numerical filtering algorithm. Different configurations of coherent two-dimensional spectroscopy of model excitonic dimer systems are investigated, with focus on the effects of intermolecular transfer coupling and bi-exciton interaction

Time-domain chirally-sensitive three-pulse coherent probes of vibrational excitons in proteins

The third order optical response of bosonic excitons is calculated using the Green's function solution of the Nonlinear Exciton Equations (NEE) which establish a quasiparticle-scattering mechanism for optical nonlinearities. Both time ordered and non ordered forms of the response function which represent time and frequency domain techniques, respectively, are derived. New components of the response tensor are predicted for isotropic ensembles of periodic chiral structures to first order in the optical wavevector. The nonlocal nonlinear response function is calculated in momentum space, where the finite exciton-exciton interaction length greatly reduces the computational effort. Applications are made to coupled anharmonic vibrations in the amide I infrared band of peptides. Chirally-sensitive and non sensitive signals for alpha helices and antiparallel beta sheets are compared.Comment: 26 pages, 6 figure

Sum-over-states vs quasiparticle pictures of coherent correlation spectroscopy of excitons in semiconductors; femtosecond analogues of multidimensional NMR

Two-dimensional correlation spectroscopy (2DCS) based on the nonlinear optical response of excitons to sequences of ultrafast pulses, has the potential to provide some unique insights into carrier dynamics in semiconductors. The most prominent feature of 2DCS, cross peaks, can best be understood using a sum-over-states picture involving the many-body eigenstates. However, the optical response of semiconductors is usually calculated by solving truncated equations of motion for dynamical variables, which result in a quasiparticle picture. In this work we derive Green's function expressions for the four wave mixing signals generated in various phase-matching directions and use them to establish the connection between the two pictures. The formal connection with Frenkel excitons (hard-core bosons) and vibrational excitons (soft-core bosons) is pointed out.Comment: Accepted to Phys. Rev.