Macromonomers [RPhSiO 1.5 ] 8,10,12 and [RCH CHSiO 1.5 ] 8,10,12 , where R is a conjugated group, have previously been shown to offer photophysical properties wherein excitation promotes an electron from the HOMO to an excited-state LUMO that sits in the center of the cage and allows communication between all conjugated groups, suggesting 3-D delocalization. In the current work, we explore replacing one conjugated group in [RPhSiO 1.5 ] 8 with either Me or nPr or s i m p l y r e m o v i n g o n e c o r n e r f r o m t h e c a g e , [RPhSiO 1.5 ] 7 (O 0.5 SiMe 3 ) 3 , and examine its effect on any potential LUMO that might form. We report here that such changes seem to have no effect on the existence of a 3-D LUMO-derived delocalization as witnessed by emission redshifts from the R = 4-Me-/4-CN-stilbene moieties essentially identical to those for the original [RPhSiO 1.5 ] 8 macromonomers. Of particular importance is the fact that removing one corner from the cage also has little effect on the photophysics, indeed significantly improving fluorescence emission quantum efficiencies. However, removing most of the conjugated groups on the corner missing cage (from 7 to 2), e.g., [MeStilSiO 1.5 ] 2 [PhSiO 1.5 ] 5 (O 0.5 SiMe 3 ) 3 , eliminates the red-shift, implying the absence of a LUMO inside the cage. This suggests a minimum number of groups are needed to form such a LUMO. Also, for the first time, the radiation patterns for nonlinear, optically induced magnetic scattering at elevated light intensities are reported for these compounds and shown to support the same conclusiona spherical LUMO exists inside the cage.

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, [RStilbeneSiO1.5]8,10,12, [RStilbeneSiO1.5]7[O1.5SiMe/nPr], [RStilbeneSiO1.5]7[O0.5SiMe3]3, [RStilbeneSiO1.5]8[O0.5‑SiMe3]4, and [RStilbeneSiO1.5]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)8OSi­(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 % F4TCNQ supporting excited-state conjugation; suggesting potential as p-type, doped organic/inorganic semiconductors.

Bromination and iodination of title double decker (DD) phenylsilsesquioxane macromonomers occurs at ortho and para positions, respectively, as in PhT8,10,12 cages. Heck cross-coupling with 4-Me/CNstyrene gives the corresponding 4-Me/CNstilbene-substituted cages. All compounds were characterized by FTIR, MALDI-TOF, TGA, NMR and GPC. These compounds show UV–vis absorptions very similar to individual stilbene analogues. However, emission for all macromonomers, except p-MeStil2Ph6DD­(OTMS)4, is redshifted 50–70 nm as seen before in full and partial cages centered LUMOs conjugated to all the stilbene moieties suggesting semiconducting behavior. Cage-centered LUMO formation even occurs in a DD cage where two of four Si–O–Si bridges are broken suggesting that LUMO formation is an extremely common phenomenon. These results are supported by both modeling studies and nonlinear light scattering in which magnetic dipole moments form and scatter light in the cage centers. The exception behaves like p-methylstilbene in both absorption and emission indicating that the onset of semiconducting behavior requires a minimum number of substituents and points to the potential to tailor band gaps and therefore multiple photophysical properties.