Theory
Introduction
Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. As a model system, we have investigated the role of topology on energy transfer efficiency in bacterial photosynthetic systems and biomimetic analogs. Using a Markovian quantum model with dissipation and trapping added phenomenologically, we elucidate a set of design principles that may be incorporated in artificial pigment-protein constructs in a supramolecular assembly. We show that our scheme reproduces many of the most salient features found in natural counterparts, which may be largely explained by simple electrostatic considerations. For instance, we correctly predict the number of pigments per ring (Fig.2 in paper), the energy spectrum of individual LH2 PPCs, and the timescale of transfer between rings. More importantly, our model clearly shows that the role of quantum mechanics extends beyond increasing transfer efficiency,as it provides remarkable robustness to both spectral and spatial disorder.
Figure 2 - Dipole moment orientation shown in top right. Optimal number of elements per ring as found by a genetic algorithm. Average trapping time as a function of the number of elements, N, in each ring. The diameter of each ring is 5 nm. The top row of images shows the strength of electrostatic coupling (lines between sites). Color of connecting lines indicates the dephasing rate between two sites. Color of circles at each site corresponds to their energies. The bottom row of images shows the average residence time at each site. The average trapping time is the sum of the average residence times at each site.
