Optical measurements reveal the charge-ordered nature of the insulating state in the chiral molecular conductors ${{\text{[(S,S/R,R)-DM-EDT-TTF]}}_2\mathrm{ClO}}_4$ (DM-Cl) and ${{\text{[(S,S/R,R)-DM-EDT-TTF]}}_2\mathrm{ReO}}_4$ (DM-Re). These enantiopure materials exhibit metallic conductivity at room temperature and a metal-insulator transition upon cooling below ${\mathrm{T}}_{\mathrm{MI}}=40$ and 105 K, respectively. Optical conductivity spectra display a polarization-independent in-plane response, attributed to the hexagonal structure of the conducting DM-EDT-TTF layer, featuring broadband electronic excitations, molecular vibrational modes, and a Drude component in the metallic phase. The gap opening at 150 and $250 {\mathrm{cm}}^{-1}$ for DM-Cl and DM-Re, respectively, signals the transition from a metallic to an insulating state upon cooling. Drude-Lorentz-Fano analysis of the optical spectra yields Hubbard parameters, the intersite Coulomb repulsion $V$ and the bandwidth $W$, supporting the presence of charge order in the insulating phase. Raman spectra of DM-Cl and DM-Re, focusing on charge-sensitive molecular vibrations, further confirm a charge-ordered insulating state with a charge disproportionation of $0.10e$ and $0.13e$, respectively. Strong DM-EDT-TTF molecular modes, activated in optical spectra through coupling with the electronic background, support the presence of lattice frustration.

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• Charge order
• Chirality
• Metal-insulator transition
• Optical conductivity
• Organic electronics
• Infrared spectroscopy
• Raman spectroscopy