The preparation of 4,5-dimethylsilylene- or 4,5-tetramethyldisilylene-bridged 9-silafluorenes was achieved by lithiation of 2,2',6,6'-tetrabromobiphenyls followed by silylation with dichlorodimethylsilane or 1,2-dichloro-1,1,2,2-tetramethyldisilane, respectively. X-ray analysis of the silylene-bridged silafluorene revealed that the molecular framework was perfectly planar and four Si-C(methyl) sigma bonds were completely orthogonal to the plane. Both the silicon atoms and the benzene rings were significantly deformed from the normal tetrahedral and hexagon shapes, respectively. The silicon bridge at the 4,5-positions was found to induce a red shift of the absorption and fluorescence spectra measured in cyclohexane, compared with 9-silafluorenes. It is remarkable that the disilylene-bridged silafluorene emitted blue light (lambda(em)=450 nm) with a large Stokes shift. The emission maxima of the silicon-bridged silafluorenes in thin films were similar to those measured in cyclohexane solution. DFT calculations suggested that introduction of the silicon bridge led to increases in both the HOMO and LUMO levels compared with 9-silafluorene.

Synthesis and X-ray diffraction analysis of 9- and 9,10-tris(trimethylsilyl)silyl (TTMSS)-substituted anthracenes were carried out to disclose that one of the Si–Si σ-bonds in the TTMSS-substituted anthracenes were perpendicular to the aromatic rings. The introduction of the TTMSS groups induced red shift of UV absorption and fluorescence emission maxima as compared with the parent and 9-pentamethyldisilanylated anthracenes. Theoretical calculation suggests LUMO levels of the TTMSS-substituted anthracenes are lowered by σ*–π* orbital interaction.

Treatment of 1,1,3,3-tetrakis(alkylthio)-2-silapropanes with t-BuLi in THF at -40 °C generated 1,1,3,3-tetrakis(alkylthio)-1,3-dilithio-2-silapropanes which reacted with various bifunctional chlorosilanes to give the corresponding 4-to 7-membered polysilacycloalkanes in moderate to good yields. Furthermore, double alkylation of the dilithiated silanes with bis(halomethyl)diorganosilanes or dihaloalkanes was found to proceed smoothly giving rise to 1,4-disilacyclohexanes or silacycloalkanes in good yields, respectively, in THF and an aprotic polar co-solvent such as hexamethylphosphoric triamide (HMPA) or 1,1,3,3-tetramethylurea (TMU). The sulfenyl groups in the cyclized products were smoothly removed by radical reduction with tributyltin hydride.

We prepared 2,3,5,6,7,8-hexasilabicyclo[2.2.2]octan-1-yl-substituted biphenyl, terphenyl, and tolan, and observed that introduction of the polysilacage group into arenes induced bathochromic shifts of absorption maxima and enhancement of molecular extinction coefficients, compared with the parent π-conjugated arenes, in addition to increase in fluorescence quantum yields.