Di-amidosils with tunable structure, morphology and emission quantum yield: the role of hydrogen bonding

Abstract

Tailoring of the structure (from amorphous to highly ordered lamellar), morphology (from a homogenous texture to fibers, microparticles, seaweeds- and desert rose-like shapes) and photoluminescence features of five di-amide crossed-linked decyl/siloxanes (di-amidosils, d-A(10)) was achieved via sol-gel chemistry and self-assembly from a single precursor through a fine control of the reaction conditions (water content, catalyst presence/type (HCl or NaOH)/concentration and co-solvent presence/type (ethanol or DMSO)). All the hybrids analyzed are multi-wavelength emitters under UV/visible excitation. Irrespective of the degree of order of the materials, the highest emission quantum yield values (ca. 013 +/- 0.01 excited at 400 nm) were found in samples synthesized in the presence of a catalyst. Comparison of the present data with those reported by our group for a shorter chain di-amidosil and for mono-amidosils revealed that in the amidosils the emission quantum yield is intimately associated with the degree of order of the amide-amide hydrogen-bonded network. This enabled us to establish for the first time a rational and straightforward way of predicting grosso modo the magnitude of the emission quantum yield of an amidosil hybrid prior to measurements, which requires simply the analysis of the amide I band of the FT-IR spectrum. This correlation opens the way to exciting new prospects for the design of new luminescent organic-inorganic hybrids with enhanced properties.