Vibrational coherence transfer and trapping as sources for long-lived quantum beats in polarized emission from energy transfer complexes

We entertain vibrational coherence transfer and related processes as possible sources for certain long-lived quantum beats observed in time-resolved polarized emission signals from photosynthetic light harvesting complexes. Signal calculations on a dimer model in which each chromophore supports a single vibrational mode show that coherence transfer to the acceptor and coherence trapping in the donor can increase the longevity of vibronic quantum beats beyond the time-scale for electronic energy exchange. These mechanisms imply an active role for coherent vibrational motion in the time-course of ultrafast energy transfer and suggest that external control over vibrations may provide a means for influencing the transport of electronic excitations. The effects of vibrational coherence transfer and trapping on excitation transfer are most vivid when the excitation-vibration coupling strength exceeds that for energy transfer. In light of the strong transfer coupling of photosynthetic light-harvesting complexes, we also examine the adiabatic energy-transfer regime, in which the relative coupling strengths are reversed.