Abstract
Amine-functionalized bridged silsesquioxanes (BSs) were synthesized from bis[(3-trimethoxysilyl)propyl] amine via a solvent-mediated route. BS-1 and BS-2 were obtained at neutral pH with sub- and stoichiometric amounts of water, respectively, and high tetrahydrofuran content. BS-3 was prepared with hyperstoichiometric water concentration, high tetrahydrofuran content, and hydrochloric acid. BS-4 was synthesized with hyperstoichiometric water concentration, high ethanol content, and sodium hydroxide. BS-1 and BS-2 were produced as transparent films, whereas BS-3 and BS-4 formed white powders. Face-to-face stacking of flat or folded lamellae yielded quasi-hydrophobic platelets with emission quantum yields of 0.05 ± 0.01 (BS-1 and BS-2) or superhydrophilic onion-like nanoparticles with exciting emission quantum yields of 0.38 ± 0.03 (BS-3) and 0.33 ± 0.04 (BS-4), respectively. The latter two values are the largest ever reported for amine-functionalized siloxane-based hybrids lacking aromatic groups. Fast Grotthus proton hopping between = / = NH groups (BS-3) and = N−/ = NH groups (BS-4), promoted by H+ and OH− ions, respectively, and aided by short amine-amine contacts provided by the onion-like morphology, account for this unique optical behavior.
Highlights
Bridged and non-bridged organosilanes [(RO)3-Si–R’–Si(OR)3 and R’–Si(OR)3, respectively] are key precursors for the development of bridged silsesquioxanes (BSs) and non-bridged silsesquioxanes (NBSs), respectively
The 13C Cross Polarization (CP)/Magic Angle Spinning (MAS) and 29Si MAS NMR spectra of the BS-1, BS-2, BS-3, and BS-4 hybrids are reproduced in Figures 2A,B, respectively, and assigned in Table 1 (Park et al, 2010)
We propose that in the very early stages of the synthesis mechanism of BS-1 the addition of ethanol, water and THF to bis[(3-trimethoxysilyl)propyl] amine (BTMSPA) resulted in the formation of an organobis(silanetriol) compound (A, Figure 8)
Summary
Bridged and non-bridged organosilanes [(RO)3-Si–R’–Si(OR) and R’–Si(OR), respectively] are key precursors for the development of bridged silsesquioxanes (BSs) and non-bridged silsesquioxanes (NBSs), respectively. If prepared by the sol-gel process solely, BSs are obtained as transparent amorphous xerogels. Ordered BSs with hierarchical nanostructures and well-defined morphologies at the macroscopic scale may be produced, if the sol-gel method. Luminescent Amine-Functionalized Bridged Silsesquioxanes is combined with self-assembly routes (Loy and Shea, 1995; Moreau et al, 2001; Lerouge et al, 2006; Shimojima and Kuroda, 2006). In the latter case, two approaches are possible: structuring may be achieved either in the absence or in the presence of structure directing agents (self-directed assembly or templateassisted self-assembly, respectively)
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