Coherent dynamics in ultrafast charge-transfer reaction of plastocyanin

Using a blue copper protein, plastocyanin, we have studied protein dynamics associated with optical excitation and radiationless deactivation (τ=270 fs) of its charge-transfer state by ultrafast pump–probe spectroscopy. A coherent low frequency (33 cm−1) vibrational mode with its phase shifted from those of the other localized Raman modes was observed. The observed coherency of this low frequency mode appears via the excited-state deactivation, rather than arising merely from impulsive stimulated Raman. This mode most probably can be attributed to the delocalized mode including the protein skeletal motion.