Exciton coupling induces vibronic hyperchromism in light-harvesting complexes

Abstract

The recently suggested possibility that weak vibronic transitions can be excitonically enhanced in light-harvesting complexes is studied in detail. A vibronic exciton dimer model that includes ground-state vibrations is investigated using the multi-configuration time-dependent Hartree method with a parameter set typical to photosynthetic light-harvesting complexes. The absorption spectra are discussed based on the Coulomb coupling, the detuning of the site energies, and the number of vibrational modes. Fluorescence spectra calculations show that the spectral densities obtained from the low-temperature fluorescence line-narrowing measurements of light-harvesting systems need to be corrected for the effects of excitons. For the J-aggregate configuration, as in most light-harvesting complexes, the true spectral density has a larger amplitude than that obtained from the measurement.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. − 180 cm 1 region, there are a few modes with the total S reaching almost 0.05 [27,28], but even this is too weak to produce significant oscillatory New J. Phys. 16 (2014) 045010 J Schulze et al New J. Phys. 16 (2014) 045010 J Schulze et al 180 cm 1 . Excitonic coupling between these two molecules is negative, with values from about −50 to − − 75 cm 1 [29]. Fluorescence line-narrowing spectroscopy has revealed that New J. Phys. 16 (2014) 045010 J Schulze et al New J. Phys. 16 (2014) 045010 J Schulze et al 7 New J. Phys. 16 (2014) 045010 J Schulze et al 8 New J. Phys. 16 (2014) 045010 J Schulze et al 9 New J. Phys. 16 (2014) 045010 J Schulze et al 10 New J. Phys. 16 (2014) 045010 J Schulze et al

Exciton–vibrational coupling in the dynamics and spectroscopy of Frenkel excitons in molecular aggregates

“…Recently, it was pointed out that in excitonic systems like FMO the observed S in selectively excited fluorescence can be significantly different from the true value of the monomer [25]. This is illustrated in Fig.…”

“…(25). Further, one can account for other Markov-type relaxation processes such as internal conversion by supplementing this set of equations with respective Markovian superoperators; cf.…”

Quantum dynamics of a vibronically coupled linear chain using a surrogate Hamiltonian approach

“…18, 86 We consider a single electronic state per molecular site. The system parameters are set to ∆E 12 = E 2 − E 1 =1274 cm −1 (=0.158 eV), τ =81 cm −1 (=0.01 eV), ω=1400 cm −1 ( ω=0.174 eV), and Huang-Rhys factor S=0.5.…”

On the origin of oscillations in two-dimensional spectra of excitonically-coupled molecular systems

“…However, long-lived vibrational coherences are common and are not expected to strongly affect the light harvesting. Identifying the nature of this coherence, specifically the details of the involvement of vibrational effects into the excitonic dynamcis, has thus become a hotly debated issue [19,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].The decoherence rate reflects the magnitude of frequency fluctuations which arise from the coupling to the surroundings. Vibrational transitions have small fluctuations since the solvent interactions are not very sensitive to the vibrational state.…”