Photophysical Properties of Functionalized Double Decker Phenylsilsesquioxane Macromonomers: [PhSiO_1.5]₈[OSiMe₂]₂ and [PhSiO_1.5]₈[O_0.5SiMe₃]₄. Cage-Centered Lowest Unoccupied Molecular Orbitals Form Even When Two Cage Edge Bridges Are Removed, Verified by Modeling and Ultrafast Magnetic Light Scattering Experiments

Abstract

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.

Conjugated Copolymers That Shouldn't Be

“…Our initial presumption was that these compounds should represent the limiting case where not only is there no 3D cage, but there are also two vinyl(Me/Ph)Si(O-) 2 bridges per cage in any oligomers/ polymers we might synthesize. Contrary to our original thoughts, the resulting compounds actually offer emission further red-shifted than any analogous compounds previously studied, [1][2][3][4][5][6][7]9] seeming to imply conjugation and semiconducting behavior where there should be none. In the following sections, we begin by characterizing a set of ladder copolymers and thereafter assess their photophysical properties.…”

“…[1][2][3][4][5] We recently extended this concept of excited-state 3D conjugation to sets of incomplete and modified cages including corner-missing T 8 , [R'Stilbene-SiO 1.5 ] 7 [O 1.5 SiMe/nPr], [R'StilbeneSiO 1.5 ] 7 [O 0.5 SiMe 3 ] 3 , [6] and newly developed double decker (DD) [R'StilbeneSiO 1.5 ] 8 -[OSiMe 2 ] 2 and [R'StilbeneSiO 1.5 ] 8 [O 0.5 SiMe 3 ] 4 . [7] Recent efforts on double decker SQs follow two parallel paths in their development exploring either molecular or macromolecular hybrid materials. [8] In the latter area, we recently synthesized a series of DD SQ based oligomers and polymers {vinyl(Me)Si(O 0.5 ) 2 [PhSiO 1.5 ] 8 (O 0.5 ) 2 Si(Me)vinyl-Ar, vinyl-DDvinyl-Ar} that unexpectedly exhibit conjugation that appears to involve two vinyl(Me)Si(O-) 2 bridges evidenced by significant emission red-shifts from corresponding model compounds.…”

Conjugated Copolymers That Shouldn't Be

“…Our initial presumption was that these compounds should represent the limiting case where not only is there no 3D cage, but there are also two vinyl(Me/Ph)Si(O‐) 2 bridges per cage in any oligomers/polymers we might synthesize. Contrary to our original thoughts, the resulting compounds actually offer emission further red‐shifted than any analogous compounds previously studied, [1–7, 9] seeming to imply conjugation and semiconducting behavior where there should be none . In the following sections, we begin by characterizing a set of ladder copolymers and thereafter assess their photophysical properties.…”

“…offer photophysical properties not at all reflective of organic decorated silicas but commensurate with cage centered LUMOs [1–5] . We recently extended this concept of excited‐state 3D conjugation to sets of incomplete and modified cages including corner‐missing T 8 , [R′StilbeneSiO 1.5 ] 7 [O 1.5 SiMe/nPr], [R′StilbeneSiO 1.5 ] 7 [O 0.5 SiMe 3 ] 3 , [6] and newly developed double decker (DD) [R′StilbeneSiO 1.5 ] 8 [OSiMe 2 ] 2 and [R′StilbeneSiO 1.5 ] 8 [O 0.5 SiMe 3 ] 4 [7] . Recent efforts on double decker SQs follow two parallel paths in their development exploring either molecular or macromolecular hybrid materials [8] .…”

Constructing 3D Interconnected Si/SiOx/C Nanorings from Polyhedral Oligomeric Silsesquioxane

“…), [ 10–12 ] endowing POSS with organic/inorganic properties. [ 13 ] POSS have been extensively reported as nanofiller and modifier to improve the mechanical properties and the thermal stability of polymeric materials. [ 14–16 ] Zhang et al.…”