Novel highly luminescent amine-functionalized bridged silsesquioxanes

Abstract

Amine-functionalized bridged silsesquioxanes (BSs) were synthesized from bis[(3-trimethoxysilyl)propyl] amine via a solvent-mediated route. BS-1 and BS-2 wereobtainedatneutralpHwithsub-andstoichiometricamountsofwater,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 andBS-4formedwhitepowders. Face-to-facestackingofflatorfoldedlamellaeyielded 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+2/=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.