Our objectives are to provide a comprehensive review solely concerning the synthesis and chemistries of polyhedral phenylsilsesquioxanes. The review covers the basic efforts to synthesize and characterize the compounds [PhSiO 1.5 ] 8 , [PhSiO 1.5 ] 10 , and [PhSiO 1.5 ] 12 . Thereafter, we discuss general methods of functionalizing these compounds with emphasis on electrophilic substitution to produce, for example, [NO 2 PhSiO 1.

A set of stilbene-substituted octasilicates [p-RStil(x)Ph(8-x)SiO(1.5)](8) (R = H, Me, MeO, Cl, NMe(2) and x = 5.3-8) and [o-MeStilSiO(1.5)](8) were prepared. Model compounds were also prepared including the corner and half cages: [p-MeStilSi(OEt)(3)], [p-Me(2)NStilSi(OSiMe(3))(3)], and [p-Me(2)NStilSi(O)(OSiMe)](4). These compounds were characterized by MALDI-TOF, TGA, FTIR, and (1)H 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 T(d(5%)) > 400 degrees 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-MeStilSiO(1.5)](8), which exhibits an absorption spectrum blue-shifted from trans-stilbene. However, the partial cages show emissions that are red-shifted by approximately 20 nm, as found for stilbene-siloxane macrocycles, suggesting some interaction of the silicon center(s) with the stilbene pi* orbital in both the corner and half cages. In contrast, the emission spectra of the full cages show red-shifts of 60-100 nm. These large red-shifts are supported by density functional theoretical calculations and proposed to result from interactions of the stilbene pi* orbitals with a LUMO centered within the cage that has 4A(1) symmetry and involves contributions from all Si and oxygen atoms and the organic substituents. Given that this LUMO has 3-D symmetry, it appears that all of the stilbene units interact in the excited state, consistent with theoretical results, which show an increased red-shift with an increase in the functionalization of a single corner to functionalization of all eight corners with stilbene. In the case of the Me(2)N- derivatives, this interaction is primarily a charge-transfer interaction, as witnessed by the influence of solvent polarity on the emission behavior. More importantly, the two-photon absorption behavior is 2-3 times greater on a per p-Me(2)Nstilbene basis for the full cage than for the corner or half cages. Similar observations were made for p-NH(2)stilbenevinyl(8)OS cages, where the greater conjugation lengths led to even greater red-shifts (120 nm) and two-photon absorption cross sections. Cathodoluminescence studies done on [p-MeStilSiO(1.5)](8) or [p-MeStilOS](8) powders exhibit essentially the same emissions as seen in solution at high dilution. Given that only the emissions are greatly red-shifted in these molecules, whereas the ground-state UV-vis absorptions are not changed from trans-stilbene, except for the ortho derivative, which is blue-shifted 10 nm. It appears that the interactions are only in the excited state. Theoretical results show that the HOMO and LUMO states are always the pi and pi* states on the stilbene, which show very weak shifts with increasing degrees of functionalization, consistent with the small chan...

The cubic symmetry of octafunctional octaphenylsilsesquioxanes [ROPS, (RC6H4SiO(1.5))8] coupled with a 1 nm diameter offers exceptional potential to assemble materials in three dimensions with perfect control of periodicity and the potential to tailor global properties at nanometer length scales. OPS itself is very inert and insoluble and can only be functionalized via electrophilic reactions with difficulty and with poor substitutional selectivity. However, functionalized OPS products are robust and highly soluble, offering easy purification and processing. In contrast to previous studies, we report here that OPS reacts with ICl at sub-ambient temperatures to provide (following recrystallization) [p-IC6H4SiO(1.5)]8, or I8OPS, in good yields and with excellent selectivity: >99% mono-iodo substitution with >93% para substitution as determined by H2O2/F- cleavage of the Si-C bonds to produce iodophenols. I8OPS in turn can be functionalized using conventional catalytic coupling reactions to provide sets of >93% para-substituted, functionalized compounds (alkynes, alkenes, aryl amines, phosphonates, aryl amines, polyaromatics, etc.), suggesting the potential to develop diverse nano-building blocks for the assembly of a wide variety of materials, some with novel photonic, electronic, and structural properties.

We describe the synthesis and characterization of the homologous p-iodophenylsilsesquioxanes (SQs) [p-I-C(6)H(4)SiO(1.5)](n) (n = 8, 10, 12) via ICl-promoted iodination (-40 to -60 degrees C) with overall yields of 80-90% and > 95% para selectivity following recrystallization. Characterization by NMR, FTIR, TGA, and single-crystal X-ray diffraction are reported and compared to data previously published for I(8)OPS. Coincidentally, we report a new synthesis of the elusive pentagonal decaphenyl SQ (dPS) [C(6)H(4)SiO(1.5)](10) and its characterization by NMR and single-crystal X-ray studies. These unique macromolecules possess equivalent chemical functionality but varying symmetries (cubic, pentagonal, and D(2d) dodecahedral), offering the potential to develop homologous series of functionalized star and dendrimer compounds with quite different core geometries and thereby providing the potential to greatly vary structure-property relationships in derivative compounds and nanocomposites made therefrom. We find that all three compounds decompose on heating to approximately 400 degrees C/N(2) with loss of I(2) to form robust, microporous materials with BET surface areas of 500-700 m(2)/g, pore volumes of 0.25-0.31 cm(3)/g, average pore widths of 8 A, and oxidative stabilities > or = 500 degrees C and with solid-phase morphologies varying from crystalline to mostly amorphous, as indicated by powder XRD and SEM studies. These latter findings point to important symmetry effects relating directly to packing in the crystalline phase prior to thermolysis.

Poly(bromooctaphenylsilsesquioxane)s (Br x OPS) are easily synthesized from octaphenylsilsesquioxane (OPS) via bromination with Br2/Fe in dichloromethane. For Br:OPS ratios less than 8:1, singly brominated products are obtained with 65−70% para substitution, 25−20% meta substitution and the remainder ortho. Higher ratios provide dibrominated products up to Br16OPS. Surprisingly, the disubstitution pattern is completely different with 80% 2,5 substitution (meta and ortho to Si), indicating extensive rearrangement with addition of the second bromine. Br x OPS bromo functionality is readily transformed via low temperature catalytic coupling reactions with para-substituted styrenes, tetraphenylborate, methyl methacrylate, or toluidine into the corresponding fully substituted p-stilbenes, p-biphenyls, methyl cinnamates, and diarylamines. The p-stilbenes offer unusually large red shifts and order of magnitude increases on photoluminescence quantum efficiencies over stilbene itself. Methyl methacrylate addition provides a mechanism for forming cross-linkable films and can be used in conjunction with the other functionalization reactions. Reactions with phenylacetylenes occur with concomitant formation of vinyl bromides, which appear to react further, adding second acetylene groups. The fact that each phenyl group occupies a different octant in Cartesian space, for Br≤ 8OPS primarily para, offers the opportunity to create novel eight branched, highly conjugated cores of value in their own right but also of value as three-dimensional, eight or 16 branched, aromatic cores for the synthesis of dendrimer-like and/or hyperbranched molecules.