σ–σ * conjugation Across Si─O─Si Bonds

Abstract Polysiloxanes and silsesquioxanes (SQs) are known to be insulating materials. We describe here polysiloxane copolymers where this is not the case. Thus,Me 2 VinylSi─O─SiMe 2 Vinyl/Br‐Ar‐Br copolymers exhibit conjugation via Si─O─Si bonds contrary to the widespread understanding that such linkages must be insulating. Here we describe the synthesis, characterization, and photophysical properties of [‐VinylSiMe 2 OMe 2 SiVinyl‐Ar]x copolymers; Ar = phenyl, terphenyl, stilbene, thiophene, etc. Con‐jugation is evidenced by redshifted emission λ max of copolymers vs model compounds, [(MeO) 2 SiMeVinyl‐Ar‐VinylMeSi(OMe) 2 ], electron transfer to F4TCNQ and MW (DP) depend‐ent emission red‐shifts (smaller bandgaps with increasing DP). Theoretical calculations targeting electronic structure, absorbance/emission λ max of model com‐pounds vs oligomers support conjugation via π‐dπ * orbital interactions. In the ground state, model compounds offer Si─O─Si bond angles of ≈110° on average. In the copolymers, bond angles change in the ground state averaging ≈ 140 ° and in the excited state approach 150 ° much closer to planarity, a result of conjugation. Here SiOSi bonds facilitate intersystem charge transfer (ICT) as seen in carbon based polymers. Thus, i.e, ICT in VySiOSiVycoPh likely leads to a much larger Stokes shift (≈115 nm) than in the silane model. Our findings provide the first detailed photophys‐ical studies of conjugation in polysiloxane‐chromophore copolymers.