AUTHOR=Pereira Rui F. P. , Nunes Sílvia C. , Toquer Guillaume , Cardoso Marita A. , Valente Artur J. M. , Ferro Marta C. , Silva Maria M. , Carlos Luís D. , Ferreira Rute A. S. , de Zea Bermudez Verónica 

TITLE=Novel Highly Luminescent Amine-Functionalized Bridged Silsesquioxanes

JOURNAL=Frontiers in Chemistry

VOLUME=5

YEAR=2018

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2017.00131

DOI=10.3389/fchem.2017.00131

ISSN=2296-2646

ABSTRACT=<p>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 = <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>/ = NH groups (BS-3) and = N<sup>−</sup>/ = NH groups (BS-4), promoted by H<sup>+</sup> and OH<sup>−</sup> ions, respectively, and aided by short amine-amine contacts provided by the onion-like morphology, account for this unique optical behavior.</p>