Synthesis and Photophysical Properties of Stilbeneoctasilsesquioxanes. Emission Behavior Coupled with Theoretical Modeling Studies Suggest a 3-D Excited State Involving the Silica Core

A set of stilbene-substituted octasilicates [p-RStilxPh8−xSiO1.5]8 (R = H, Me, MeO, Cl, NMe2 and x = 5.3−8) and [o-MeStilSiO1.5]8 were prepared. Model compounds were also prepared including the corner and half cages: [p-MeStilSi(OEt)3], [p-Me2NStilSi(OSiMe3)3], and [p-Me2NStilSi(O)(OSiMe)]4. These compounds were characterized by MALDI-TOF, TGA, FTIR, and 1H NMR techniques. Their photophysical properties were characterized by UV−vis, two-photon absorption, and cathodoluminescence spectroscopy (on solid powders), including studies on the effects of solvent polarity and changes in concentration. These molecules are typically soluble, easily purified, and robust, showing Td(5%) > 400 °C in air. The full and partial cages all show UV−vis absorption spectra (in THF) identical to the spectrum of trans-stilbene, except for [o-MeStilSiO1.5]8, which exhibits an absorption spectrum blue-shifted from trans-stilbene. However, the partial cages show emissions that are red-shifted by ∼20 nm, as found for stilbene−siloxa...