Dynamics of β-Carotene-to-Chlorophyll Singlet Energy Transfer in the Core of Photosystem II

Abstract

The core of photosystem II comprises three major subcomplexes: the photochemical reaction center (RC) and the core antennas CP43 and CP47. All contain β-carotene as the only carotenoid, but the quantum efficiency of β-carotene-to-chlorophyll singlet energy transfer in the CP43, CP47, and RC complexes is poor. From a femtosecond transient absorption study of the isolated subcomplexes following β-carotene excitation, we show that mainly the β-carotene S2 (1Bu+) state is involved in the energy-transfer process. At most, a minor amount of energy transfer from “hot” β-carotene S1 (2Ag-) states is present in CP43 and CP47, but this S1 contribution is absent in the RC. In all complexes, the relaxed S1 state is not participating in energy transfer. This absence of energy transfer from S1 states explains the low overall yield of β-carotene-to-chlorophyll singlet energy transfer in the PSII core.