White-Light Emission of Amine-Functionalized Organic/Inorganic Hybrids: Emitting Centers and Recombination Mechanisms

Photoluminescent, transparent and flexible di-ureasil hybrids containing CdSe/ZnS quantum dots

We describe, in this paper, the sol-gel synthesis of di-ureasil based nanocomposites prepared in situ in the presence of organically capped CdSe quantum dots (QDs) or CdSe QDs which have been coated with a ZnS shell. For the latter a new chemical route to coat the CdSe QDs with ZnS shells was investigated and is now reported. The QDs became well dispersed in the final nanocomposites, whose microstructural homogeneity was evaluated by atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses. In order to understand the optical behaviour of di-ureasil containing QDs, a detailed photoluminescent study was undertaken for a selected particle size distribution of ZnS coated CdSe QDs (d∼4.5 nm). Emission quantum yields up to 0.11 were measured in the final nanocomposites that present a huge (between 3 and 6 orders of magnitude) increase in the lifetime of the QDs (relative to that of isolated ones), as a result of energy transfer occurring between the intimately mixed di-ureasil host and the QDs.

Fluorophore-free luminescent organosilica nanoparticles

In this paper, we report the preparation and characterization of fluorophore-free luminescent organosilica nanoparticles (NPs) with sizes varying from 50 to 250 nm. These NPs were synthesized by the Stöber method by incorporating several organosilanes together with the silicate precursor (tetraethyl orthosilicate, TEOS) to the silica matrix. The calcination of these NPs at high temperatures (600 and 700 degrees C) led to fluorescent and phosphorescent properties, which proved to be highly dependent on the initial composition of the silanization mixture and the heating temperature. Further characterization of this material in terms of its structural and optical properties is reported. Although the NPs are not very bright, the lifetime measurements revealed values in the millisecond range, which makes these NPs potentially attractive as luminescent materials and for time-resolved optical spectroscopic studies and bioassays.

Corrosion studies and interfacial bonding of urea/poly(dimethylsiloxane) sol/gel hydrophobic coatings on AA 2024 aluminum alloy

Bis[(ureapropyl)triethoxysilane] bis(propyl)-terminated-polydimethylsiloxane 1000 (PDMSU), an organic-inorganic hybrid, diluted in either EtOH or a mixture of EtOH-PrOH, was used in thin film form (<200 nm) to inhibit the corrosion of AA 2024 alloy. Potentiodynamic, time-dependent cyclovoltammetric measurements and salt spray tests showed that the corrosion inhibition of the latter was 10 times higher than that of the former films. This was correlated with the higher degree of hydrolysis and the formation of more open polyhedral silsesquioxane species (T2) in the bulk heat-treated PDMSU/EtOH-PrOH xerogels (29Si NMR spectra). The structure of the coatings deposited on AA 2024 Al alloy was deduced from the infrared reflection-absorption (IR RA) spectra, which revealed more extensive urea-urea interactions and more efficient silane-Al interface bonding for the PDMSU/EtOH-PrOH coatings with higher corrosion inhibition. Ex situ IR RA potentiodynamic spectroelectrochemical measurements of PDMSU coatings revealed that their degradation did not proceed via the formation of silanol groups and consequent hydration of the coatings but that they decomposed above E(corr) by forming fragments composed of -CH2- segments in an all-trans conformation.

Structural and water-repellent properties of a urea/poly(dimethylsiloxane) sol-gel hybrid and its bonding to cotton fabric

A novel diureapropyltriethoxysilane [bis(aminopropyl)-terminated-poly(dimethylsiloxane) (1000)] (PDMSU) sol-gel hybrid was synthesized and applied on cotton to make it water repellent. Surface-energy values of PDMSU deposited on an aluminum substrate were determined, and the contact angle for water was assessed for impregnated cotton fabrics. The stability of the coatings was determined by repetitive washing, and their degradation was investigated with the help of the infrared attenuated total reflection (ATR) technique. The structure of PDMSU was studied by ATR and 29Si NMR spectroscopy. The results showed the active role of the urea groups in PDMSU/cotton interface bonding, but washing led to the relaxation of the urea-urea associations, as inferred from the appearance of a new amide II band at 1541 cm(-1).

Novel self-protective phosphorescence from crystalline nanoparticles assembled by 3-bromo- and 3-iodo-carbazoles based on halogen–halogen interaction in suspension solutions

The crystalline nanoparticles can be assembled by 3-bromo- and 3-iodo-carbazole (3-BrC and 3-IC) based on the halogen-halogen interaction in suspension aqueous solutions. As the colloid-like suspension was dropped onto film the particles further aggregate as rod-like structures with size of 3 microm in length and 1 microm in width. The halogen-halogen interaction are well proved by single crystal X-ray data, and the data reveal that each bromine atom interacts with the neighboring two, and each iodine atom interacts with the neighboring five and I-I interaction is stronger than that of Br-Br. Both 3-BrC and 3-IC can emit novel self-protective room temperature phosphorescence (RTP) in the range of 480 to near 800 nm at the excitation of 338 nm, and 3-BrC shows additionally the delayed fluorescence emission from 350 to 480 nm, both possessing the charge-transfer character caused by halogenations. RTP decay possesses the bi-exponential property and RTP lifetimes are 3.37, 31.16 ms (with ethanol) and 1.52, 30.83 ms (with THF) for 3-BrC or 3.53, 14.95 ms (with ethanol) and 1.68 ms, 13.74 ms (with THF) for 3-IC, showing " heavier atom ", I, makes intersystem crossing rate k(ISC) from both S1 to T1 and T1 to S(0) faster. For the results, the detection limits of 3-BrC and 3-IC can reach 2.4 x 10(-7) and 9.0 x 10(-8)mol L(-1), respectively, with wider linear range and higher precision compared with other systems.

Local Structure and Near-Infrared Emission Features of Neodymium-Based Amine Functionalized Organic/Inorganic Hybrids

Nd(3+)-based organic/inorganic hybrids have potential application in the field of integrated optics. Attractive sol-gel derived di-urea and di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils and di-urethanesils, respectively) doped with neodymium triflate (Nd(CF(3)SO(3))(3)) were examined by Fourier transform mid-infrared (FT-IR), Raman (FT-Raman), (29)Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and photoluminescence spectroscopies, and small-angle X-ray scattering (SAXS). The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the photoluminescence properties. The main conclusion derived from this study is that the hydrogen-bonded associations formed throughout the materials play a major role in the hybrids nanostructure and photoluminescence properties.

Eu3+ Coordination in an Organic/Inorganic Hybrid Matrix with Methyl End-Capped Short Polyether Chains

Fourier Transform mid-infrared (FT-IR), Fourier Transform Raman (FT-Raman) and photoluminescence spectroscopies and Two-Dimensional (2D) Correlation Spectroscopic Analysis were employed to examine the anionic and cationic local environments in mono-urethanesils doped with europium triflate (Eu(CF(3)SO(3))(3)). The hybrid host framework of these materials is composed of a siliceous backbone bonded through urethane linkages to CH(3)-terminated polymer chains containing about 7 OCH(2)CH(2) units. Samples with infinity >/= n (composition) >/=5 (where n = OCH(2)CH(2)/Eu(3+)) were studied. In terms of ionic association, the level of complexity of these xerogels is very high. In all the compounds the triflate ions exist "free", weakly coordinated and forming cross-link separated ion pairs. At 20 >/= n >/= 5, in addition to all these species contact ion pairs occur. In agreement with these conclusions, photoluminescence establishes the presence of three distinct cation local sites (Eu(3+)/O=C(urethane cross-links), Eu(3+)/O-C-C(polyether chains) and weakly coordinated Eu(3+)/CF(3)SO(3)(-) ionic pairs).