Molecules with perfect cubic symmetry as nanobuilding blocks for 3-D assemblies. Elaboration of octavinylsilsesquioxane. Unusual luminescence shifts may indicate extended conjugation involving the silsesquioxane core

Richard Laine

S. Sulaiman, A. Bhaskar, J. Zhang, R. Guda, T. G III, and R.M. Laine (2008)

Chem Mater., 20:5563 – 5573.

The objectives of this work are to demonstrate facile routes to 3-D star materials with octa- and hexadecafunctionality to provide new nanoconstruction tools for the synthesis of new types of stars, dendrimers, and hyperbranched molecules or for the assembly of novel nanocomposites. A further objective is to identify novel properties inherent in the resulting new compounds. Octavinylsilsesquioxane (OVS, [VinylSiO1.5]8) with perfect 3-D or cubic symmetry is elaborated through metathesis with substituted styrenes to produce a series of RStyrenylOS compounds. The p-BrStyrenylOS compound is then further reacted with other sets of p-substituted styrenes via Heck coupling to produce a set of R′VinylStilbeneOS compounds. The R′ = NH2 compound is then reacted with 3,5-dibromo or dinitrobenzoyl chloride to produce hexadecafunctional 3-D stars. These synthetic methods provide perfect single core and then core−shell 3-D stars including in the third generation branch points such that these molecules can be used for the synthesis of new dendrimers or hyperbranched molecules. Further, the first sets of materials are fully conjugated. Investigation of the UV−vis absorption, photoluminescence, and two-photon absorption properties of the R′VinylStilbeneOS compounds, especially where R′ = NH2, reveals exceptional red-shifts (120 nm), charge-transfer behavior, and excellent two-photon absorption properties that may suggest that the silica core serves the role of electron acceptor in the system and interacts equally with all eight organic moieties. This observation may imply 3-D conjugation through the core.

silsesquioxanes, photophysical property