Effects of the exciton-exciton coherence transfer (EECT) in strongly coupled molecular aggregates are investigated from the reduced time-evolution equation which we have developed to describe EECT. Starting with the nonlinear response function, we obtained explicit contributions from EECT to four-wave-mixing spectrum such as photon echo, taking into account double exciton states, static disorder, and heat-bath coupling represented by arbitrary spectral densities. By using the doorway-window picture and the projection operator technique, the transfer rates between two different electronic coherent states are obtained within a framework of cumulant expansion at high temperature. Applications of the present theory to strongly coupled B850 chlorophylls in the photosynthetic light harvesting system II (LH2) are discussed. It is shown that EECT is indispensable in properly describing ultrafast phenomena of strongly coupled molecular aggregates such as LH2 and that the EECT contribution to the two-dimensional optical spectroscopy is not negligible.
Bibliographical noteFunding Information:
This research is partially supported by Grant-in-Aids for Scientific Research from Japan Society for the Promotion of Science, Grant Nos. 17740278 and A 15205005. One of the authors (M.C.) is grateful for financial support from the CRI program of KOSEF (MOST, Korea). Another author (K.H.-D.) also appreciates useful technical support from T. Hasegawa and fruitful discussion with A. Kimura.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry