3-D Molecular Mixtures of Catalytically Functionalized [vinylSiO1.5]10/[vinylSiO1.5]12. Photophysical Characterization of Second Generation Derivatives

Fluoride ion catalyzed rearrangement of -[vinylSiO(1.5)](n)-oligomers and polymers in THF (tetrahydrofuran) provides essentially quantitative conversion to mixtures of the three dimensional (3-D) cage compounds [vinylSiO(1.5)](10) and [vinylSiO(1.5)](12) with small amounts of the [vinylSiO(1.5)](14) cage. These mixtures are easily transformed into their respective styrenyl analogs by metathesis with p-R-styrene to give 100% conversion to the Generation 1 (GEN1) compounds [p-R-styrenyl-SiO1.5](10/12). The R = Br compounds are then easily modified by Heck coupling with p-R-styrene in >90% yields and approximate to 100% conversion to the Generation 2 (GEN2) compounds [p-R-stilbenevinylSiO(1.5)](10/12). These studies were designed to map structure-photophysical properties in these 3-D molecules with the goal of finding replacements for C-60 and C-70 electron acceptor compounds currently in use in most hybrid organic photovoltaics. Photophysical characterization indicates that the GEN2 compounds have average band gaps that are slightly smaller than their T-8 analogs. However, the C6F5 derivative offers blue-shifted absorption with a very red-shifted emission in contrast to the blue emission shift that was expected coincident with the absorption blue shift. Initial cyclic voltammetry studies suggest that the GEN2 C6F5 derivative has HOMO-LUMO energies that may, through further modification, provide energy levels that meet our target objectives. In addition, solvent studies targeting absorption and emission behavior find emission behavior in poor solvents for R = H, Me, MeO that suggests some form of aggregation. This aggregation red shifts emission, perhaps arising from partial interdigitation of p-R-stilbenevinyl groups. Because these molecules are 3-D, moieties opposite the points of interdigitation emit as they do in good solvents, leading to emissions that broadened greatly. Furthermore, because we have previously observed what appears to be 3-D conjugation in the excited state, these results suggest the potential to promote charge transport in three dimensions perhaps similar to C-60/C-70. Alternately, these same materials may serve as novel emitters for light emitting diodes.