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From the ESR spectra of anion radicals of bis(4-biphenylyl)dimethylsilane and 4,4′-bis(4-biphenylyldimethylsilyl)biphenyl, the delocalization of spin density is inferred. The bridging SiMe2-groups separate practically independent π-systems. The rate of electron transfer between biphenyl sub-units is less than ∼ 106 sec−1 at 223 K.

The zero-field splitting parameters D and E, or D, were measured by electron spin spectroscopy for the triplet states of bis(4-biphenylyl)dimethylsilane, 4,4′-bis-(4-biphenylyldimethylsilyl)biphenyl, 1,2-diphenyltetramethyldisilane, several monosilanes, bis(4-biphenylyl)methane, 4,4′-bis(4-phenylbenzyl)biphenyl, and dimethyldiphenylmethane. The zero-field splitting values of compounds having biphenyl subunits bridged with either SiMe2- or CH2-groups, compared with those of mono- and disubstituted biphenyls, show that the triplet electrons are localized mainly on one biphenyl group in each of the bridged compounds on the time scale of the ESR observations.

For the compounds C 6 H 5 C 6 H 4 YC 6 H 4 C 6 H 5 and C 6 H 5 C 6 H 4 YC 6 H 4 C 6 H 4 YC 6 H 4 C 6 H 5 where Y is either Si(CH 3 ) 2  or CH 2 , reduction potentials and p -band positions are reported. These data as well as the UV data for several phenyl derivatives are consistent with silicon blocking, to a large extent, conjugation (little or no through conjugation) of biphenyl moieties separated by Si(CH 3 ) 2 groups.