Closer analysis of the MOs and of the character of the electronic excitations shows that the degenerate HOMO in 6 is genuinely nonbonding (with dxy and dx²-y² character) and thus also changes very little (by less than 0.15 eV) upon expanding the Fe-C distances and upon finally adding the DMS substituents. This is consistent with the small effect of the silyl substituents on the redox potentials (see above). The low-lying excitations are out of this HOMO and out of another high-lying occupied MO with predominant metal dz² character. This MO, which is very slightly -antibonding, drops in energy by about 0.25 eV upon bond expansion but goes up by 0.17 eV when adding the DMS substituents, thus staying also almost unchanged overall compared to [FeCp2]. The changes in the band gap and low-lying excitation energies from [FeCp2] to 6 are thus largely due to changes in the virtual MO energies. In particular, the (twofold degenerate) LUMO comes down by 0.47 eV upon bond-lengthening and by another 0.20 eV upon adding the DMS substituents. The LUMO is clearly π-antibonding and becomes less antibonding for the silyl-substituted ferrocenes, thus explaining the bathochromic shifts.