To explain these findings, density functional theory (DFT) calculations were performed, comparing unsubstituted ferrocene, [FeCp2], with the persilylated derivative (6) (ωB97X-D/def2-TZVPP(D)//r 2 SCAN-3c level, see ESI for details). For [FeCp2] the expected D5h symmetric minimum is found, with the usual D5d transition state for rotation of the Cp ligands (at a free energy of about 5 kJ/mol, consistent with the well-known free rotation in solution ). Time-dependent DFT calculations of the lowest excitation energies give a band at λ = 461 nm, for a 1 A1 → 1 E1 transition (in D5 notation) and two additional bands at λ = 351 nm and 512 nm, arising from the second 1 A1 → 1 E1 and the formally forbidden 1 A1 → 1 E2 transitions, respectively (ESI, Figure ). The overall spectrum agrees very well with the experimentally determined spectrum. It is likely that the closeness of the two lowest excitation energies and the similar intensities (when also considering contributions from the D5d transition state) lead to a broadening of the peak, without a clearly discernible shoulder.