Photoluminescence of Bridged Silsesquioxanes Containing Urea or Urethane Groups with Nanostructures Generated by the Competition between the Rates of Self-Assembly of Organic Domains and the Inorganic Polycondensation

Abstract

The aim of this study was to investigate the changes produced in the nanostructures and the photoluminescence spectra of bridged silsesquioxanes containing urea or urethane groups, by varying the relative rates between the self-assembly of organic domains and the inorganic polycondensation. Precursors of the bridged silsesquioxanes were 4,4‘-[1,3-phenylenebis(1-methylethylidene)]bis(aniline) and 4,4‘-isopropylidenediphenol, end-capped with 3-isocyanatopropyltriethoxysilane. The inorganic polycondensation was produced using either high or low formic acid concentrations, leading to transparent films with different nanostructures as revealed by FTIR, SAXS, and 29Si NMR spectra. For the bridged silsesquioxanes containing urea groups the self-assembly of organic domains was much faster than the inorganic polycondensation for both formic acid concentrations. However, the arrangement was more regular and the short-range order higher when the rate of inorganic polycondensation was lower. The photoluminescence spectra of the most ordered structures revealed the presence of two main processes: radiative recombinations in inorganic clusters and photoinduced proton-transfer generating NH2 + and N- defects and their subsequent radiative recombination. In the less-ordered urea-bridged silsesquioxanes a third process was present assigned to a photoinduced proton transfer in H-bonds exhibiting a broad range of strengths. For urethane-bridged silsesquioxanes the driving force for the self-assembly of organic bridges was lower than for urea-bridged silsesquioxanes. When the synthesis was performed with a high formic acid concentration, self-assembled structures were not produced. Instead, large inorganic domains composed of small inorganic clusters were generated. Self-assembly of organic domains took place only when employing low polycondensation rates. For both materials the photoluminescence was mainly due to radiative processes within inorganic clusters and varied significantly with their state of aggregation.

Luminescence Enhancement after Adding Stoppers to Europium(III) Nanozeolite L

“…[39] This means that no obvious hydrolysis occurs during the sonication procedure. The bands at 1556 and 1462 cm À1 belong to the imidazole ring of 1.…”

Tuning the Photoluminescence of Silsesquioxanes with Short Substituted Urea Bridges

“…[1][2][3][4][5][6][7][8][9][10][11][12] In particular, materials bearing urea groups in the organic bridge have received considerable attention in recent years due to their white light photoluminescence (PL). [13][14][15][16][17][18][19][20] Photoluminescent ureabridged silsesquioxanes are usually synthesized by the carboxylic acid solvolysis of the corresponding precursors containing terminal trialkoxysilyl groups. [16,18] In this process condensation reactions can be carried out in the absence of water, [21][22][23] leading to hybrid materials exhibiting high PL quantum yields.…”

Fast Synthesis of Nanostructured Microspheres of a Bridged Silsesquioxane via Ultrasound‐Assisted Sol–Gel Processing

“…In the case of selfassembled bridged silsesquioxanes, this characteristic distance is frequently found to be equal to the length of the organic bridges. [15,47] In our system, the appearance of diffraction patterns in the range of 0.14-1.1 Å À1 is indicative of the existence of some degree of organization at the molecular level.…”

“…Strong hydrogen bonds as those formed among urea groups, alone or combined with aromatic p-stacking or hydrophobic interactions produce a variety of self-assembled structures. [15][16][17][18][19][20][21] Recently, well-defined spherical micro and nanoparticles have attracted great attention since they have many applications in advanced technologies. Different techniques for preparing these particles at nano and micro scales, via oil/water solvent evaporation method, [22] vigorous stirring of the precursors for long periods, [23,24] among others, have been reported.…”