Unconventional Conjugation via vinylMeSi(O-)2 Siloxane Bridges May Imbue Semiconducting Properties in [vinyl(Me)SiO(PhSiO1.5)8OSi(Me)vinyl-Ar] Double-Decker Copolymers

A number of groups have invested considerable time synthesizing double-decker silsesquioxane (DD SQ) copolymers; however, to our knowledge, no one has sought to explore through-chain electronic communication between DD SQs via conjugated co-monomers. We recently demonstrated that stilbene derivatives of simple DD cages exhibit properties commensurate with formation of cage centered lowest unoccupied molecular orbitals (LUMOs), equivalent to LUMOs found in complete/incomplete SQ cages, [RStilbeneSiO(1.5)](8,10,12), [RStilbeneSiO(1.5)](7)[O1.5SiMe/nPr], [RStilbeneSiO(1.5)](7)[O0.5SiMe3](3), [RStilbeneSiO(1.5)](8)[O-0.5-SiMe3](4), and [RStilbeneSiO(1.5)](8)[OSiMe2](2). Such LUMOs support the existence of 3D excited-state conjugation in these cages. We describe here Heck catalyzed copolymerization of vinyl(Me)SiO(PhSiO1.5)(8)OSi(Me)vinyl (vinylDDvinyl) with X-Ar-X, where X = Br or I and X-Ar-X = 1,4-dihalobenzene, 4,4'dibromo-1,1'-biphenyl, 4,4 ''-dibromo-p-terphenyl, 4,4'-dibromo-trans-stilbene, 2,5-dibromothiophene, 5,5'-dibromo-2,2'-bithiophene, 2,5-dibromothieno[3,2-b]thiophene, and 2,7-dibromo-9,9-dimethylfluorene. Coincidentally model analogs were synthesized from vinylMeSi(OMe)(2). All compounds were characterized in detail by gel permeation chromatography (GPC), matrix-assisted laser desorption/ionization-time-of-flight, thermogravimetric analysis, nuclear magnetic resonance, Fourier transfer infrared spectroscopy, ultraviolet-visible spectroscopy, photoluminescence spectrometry, and two-photon absorption (2PA) spectroscopy. Modeling of HOMO-LUMO energy levels of related compounds with R = Me rather than Ph was also explored. In the current systems, we again see apparent conjugation in excited states, as previously observed, as indicated by 50-120 nm red shifts in emission from the corresponding model silane compounds. These results suggest unexpected semiconducting behavior via vinylMeSi(O-)(2) (siloxane) bridges between DD cages in polymers. The thiophene, bithiophene, and thienothiophene copolymers display integer charge transfer behavior on doping with 10 mol % F(4)TCNQ supporting excited-state conjugation; suggesting potential as p-type, doped organic/inorganic semiconductors.