TDDFT studies on the chiroptical properties of a chiral inorganic polythioanion Möbius strip

Abstract

The electronic circular dichroism (ECD) spectra of chiral inorganic polythioanion Möbius strip [(Mo₂S₂O₂)₄(OH)₆(C₄O₄) (Mo₂O₈)]⁴⁻ (1a) and its 1e- and 2e-reduced forms were investigated by using the time-dependent density functional theory (TDDFT) method. The simulated UV spectra of 1a agree well with the experimental spectra, confirming that the CAM-B3LYP hybrid functional can accurately predict the excitation energies of a polythioanion. The shapes of the ECD bands for the reduced forms are similar to that of 1a, while the rotatory strengths clearly increase with the additional electrons. The peaks in the ECD spectra of 1a are mainly assigned to the charge transfer from the {C₄O₄} unit and S atoms to the Mo and terminal oxygen (O_t) atoms. The {C₄O₄} unit is the main chiroptical chromophore. For the reduced forms, the charge transfer from S atoms to Mo atoms significantly increases with the additional electrons. It is reasonable to assume that the transfer of chirality from the {C₄O₄} unit to the {Mo₂S₂O₂} unit is generated during the reduction process.