Quantum phase synchronization revealing few-hundred femtosecond coherence in cryptophyte phycoerythrin 545 antenna from exciton–vibrational coupling

Quantum beats lasting a few hundred femtoseconds have been regarded as signatures of quantum energy transfer in photosynthetic antennae. The fragile coherence at room temperature casts doubt on its long-lived feature arising from the electronic coherence. Recently, the long-lived exciton–vibrational coherences of several hundred femtoseconds via quantum phase synchronization of the resonant higher frequency collective vibrational modes have been observed in core antenna allophycocyanin from algae. The long-lived coherence has an inherent property of protecting the coherence against the noisy environment. This is achieved by dissipation of the resonant anti-symmetric collective vibrational modes coupled to the excitonic levels, which have fast dephasing, leaving only the non-dissipative correlated symmetric modes [R. Zhu et al., Nat. Commun. 15, 3171 (2024)], which is different from that induced by the environmental low frequency modes. Coherence with a lifetime constant of 200 fs at room temperature has been observed in the cryptophyte phycoerythrin 545 (PE545) antenna before, while its origin, i.e., pure electronic or exciton–vibrational, remains to be explored. Here, we investigated coherent energy transfer dynamics in PE545 via two-dimensional electronic spectroscopy. A long-lasting coherence with a lifetime constant of 270 fs in the dynamical Stokes shift dynamics was observed. Especially, the high frequency vibrational mode at 1150 cm−1 is absent in the electronic energy dissipation process reflected in the dynamical Stokes’ shifts spectrum, which is near resonant with the electronic gap of 1080 cm−1. Therefore, the facts strongly suggest that the long-lived coherence in PE545 is realized by the resonant exciton–vibrational coupling via quantum phase synchronization.