Ref. : First, positions of hydrogen atoms only were optimized and subsequently intramolecular bond lengths were relaxed, while keeping all the remaining degrees of freedom fixed (for more details, see Ref. ). To this end, the BP86 XC functional and the def2-TZVP basis set were used. The computational cost of structure optimization was reduced by using the resolution-of-the-identity approximation with the auxiliary Coulomb fitting def2-TZV/J basis . To account for dispersion interactions, the D3BJ correction with Becke-Johnson damping were enabled. Binding pockets were initially optimized in a similar fashion as described in Ref. . To this end, we first optimized the positions of hydrogens and then relaxed the atoms of (B)Chl a and His composing the hinge-like complexes within the pocket. This approach, however, led to severe difficulties in SCF convergence during successive FDE calculations as molecular structures of amino acids covalently bond to His were not fully optimized. An alternative approach with (B)Chl a, His, and all covalently bond amino acids relaxed led to large changes in the intermolecular orientation compared to the original crystal structure. Therefore, it was decided to replace the long peptide tail connected to the His amino acid with neutral capping groups and, in addition to the two structure optimization steps described above, fully optimize their atoms keeping the remaining molecular structure fixed. The Density Functional Tight Binding (DFTB) method from the Ams-Dftb module of the Adf package in conjunction with the parameters set from the Third-Order Parametrization for Organic and Biological Systems (3ob) , and the dispersion D3BJ correction were applied in all three steps. The resulting reduced molecular structures were used without further re-optimization in succeeding spin-density calculations of the corresponding radicals.