Mapping the exciton coupling in the peridinin-chlorophyll protein from dinoflagellates by magnetophotoselection

Time-resolved electron paramagnetic resonance (TR-EPR), combined with magnetophotoselection (MPS), provides a powerful approach to probe exciton states in multichromophoric systems where photoexcitation populates a triplet state localized on a specific chromophore. This scenario occurs in the peridinin-chlorophyll protein (PCP) from dinoflagellates, which contains clusters of peridinins surrounding chlorophyll a. Here, we present MPS-TR-EPR data for PCP from Heterocapsa pygmaea and a high-salt PCP variant from Amphidinium carterae. Spectral analysis reveals the orientation of the optical transition dipole moments (TDMs), reflecting the chromophore contributions to the exciton states. The results indicate a predominant role of Per614/624 in the lowest singlet exciton state, consistent with theoretical models, while, at the same time, also suggesting refinements to better align the models with the experimentally determined TDM orientations. These findings provide constraints relevant to understanding molecular strategies for optimizing light absorption and energy transfer in light-harvesting complexes.