Excitation energy equilibration in a trimeric LHCII complex involves unusual pathways.

We explore the energy equilibration within the LHCII trimer using various approaches, including the Redfield-Förster method (with different compartmentalization schemes) and the exact hierarchical equation of motion (HEOM). We demonstrate that the inter-monomeric migration in the trimeric LHCII complex is not limited to direct transfers between quasi-equilibrated chlorophylls (Chls) , but also involves additional pathways with uphill transfers from Chls to the stromal-side Chls (connecting the Chls clusters from different monomeric subunits). Although these uphill transfers are slow they still can increase the total rate of inter-monomeric transfers by a factor of 1.5. The same stromal-side Chls also promote a depopulation of the Chl 604 long-lived state (blue-shifted and mixed with the lumenal-side Chls ). Due to the connection between the stromal- and lumenal-side Chls clusters the intra- and inter-monomeric transfers from 604 to the main Chls become faster by a factor of 1.6 and 1.75, respectively.