In contrast to this, the UV/VIS spectra of isolated silylferrocenes 3-6 indicate decreasing HOMO-LUMO energy gaps. Those spectra were recorded in n-hexane (Figure ). Unsubstituted ferrocene exhibits an absorption band at λ = 441 nm in the visible regime corresponding to the unresolved 1 A1 → 1 E1 and 1 A1 → 1 E2 spin-allowed d-d transitions, explaining the orange color of this compound. Incorporation of dimethylsilyl groups causes a bathochromic shift yielding a color transition from red to purple from heptakis-to decakis(dimethylsilyl)ferrocene. This shift has been observed in previously reported polysilylated ferrocenes as well. However, in the spectra of silylferrocenes 3-6 this band is accompanied by a shoulder which is most pronounced in the spectrum of FeC10DMS10 (6).