On Sub-Sevenfold Symmetries in LH2 Stacked Ring Scaffolds: A Quantum Optical Perspective

Abstract

Using a closed quantum optical coupled-dipole model, we investigate why sub-sevenfold symmetries are likely absent in the stacked-ring scaffolds of light-harvesting 2 (LH2) complexes in purple photosynthetic bacteria.

Figures (2)

• Figure 1: Collective energy shift $(\Omega^n_m)$ for different angular momentum eigenmode $m$ in LH2 ring geometries having ninefold ($C_9$) (a), eightfold ($C_8$) (c) and sevenfold ($C_7$) (e) symmetries. An example schematic of stacked LH2 scaffold with $C_9$ symmetry is being displayed in the inset of the panel (b), with top ring $R_1$ and bottom ring $R_2$. The energy band separation ($\Delta \Omega_m = (\Omega^2_{m} - \Omega^3_{m})/\Gamma_0$) for mode $m =-1$ with variable transition wavelength $\lambda$ for the optical dipoles of $R_2$ are plotted for $C_9$(b), $C_8$(d) and $C_7$(f) symmetry (keeping the ring-size unaltered). The minimum band separation (denoted via the vertical lines) hints for the photo-activity of the optical dipole in ring $R_2$, where the ring $R_1$ has all 800 nm dipoles and the respective $\Gamma_0 \sim 25.7$ MHz. Required geometric parameters for simulation are taken from Ref. montemayor:jpcb:2018 (for panels (a),(b)) and Ref. pal:njp:2025 (for panels (c)-(f)), respectively.
• Figure 2: (a) Collective energy shift $(\Omega^n_m/\Gamma_0)$ for assumed sixfold $C_6$ symmetries with angular momentum quantum number $m$. Table-\ref{['tab1']} illustrates the geometric parameters in use for this assumed geometry. The energy band separation, i.e., $\Delta \Omega_{-1} = (\Omega^2_{-1} - \Omega^3_{-1})/\Gamma_0$, for variable transition wavelength $\lambda$ corresponding the optical dipole of bottom ring $R_2$ are plotted for $C_6$(b) symmetry (all other parameters are fixed). The smallest band separation are being denoted via the vertical lines in panel (b). Top ring $R_1$ has all 800 nm dipoles.