Coupling Photoluminescence and Ionic Conduction Properties Using the Different Coordination Sites of Ureasil-Polyether Hybrid Materials

In this article, we demonstrate that each functional group of ureasil organic-inorganic hybrid (OIH) materials can act as a specific coordination site for a given active guest species, hence allowing the possibility of combining different functional properties. To illustrate this concept, the sol-gel process was used to produce diurea cross-linked siloxane-polyethylene oxide (U-PEO) and siloxane-polypropylene oxide (U-PPO) hybrid host frameworks with similar molecular weights (1900 and 2000 g mol^-1 for PEO and PPO, respectively), with Li⁺ and Eu³⁺ as active guest ions providing ionic conduction and photoluminescence (PL) properties, respectively. Comparison of Fourier transform infrared spectra and small-angle X-ray scattering results for single-doped (using Li⁺ or Eu³⁺) and co-doped (using Li⁺ and Eu³⁺) U-PEO and U-PPO hosts showed that in every case, there was specific coordination of Eu³⁺ by the carbonyl group of the urea bridge and of Li⁺ by ether-type oxygen of the PEO and PPO chains. Optical analyses demonstrated that loading with Li⁺ did not affect the luminescence properties of the Eu³⁺-loaded OIH. Although loading with Eu³⁺ had a small effect on ionic transport, co-doping with Li⁺ ions ensured macroscopic ion-conduction of the transparent and luminescent hybrid material. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional devices. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional polyelectrolytes applied in the field of dual luminescent devices such as photoelectrochromic smart windows.

Delocalization of electronic states in graphene oxide stabilised mesoporous silica nanoparticles revealed using photoluminescence

Mesoporous silica aerogel obtained through a sol–gel process when surface treated with 2-D graphene oxide sheets reveals many fascinating features particularly, leading to multiple coordination complexes based on amide linkages.

Lanthanide-DTPA grafted silica nanoparticles as bimodal-imaging contrast agents

The design and synthesis of a combined MRI-optical probe for bio-imaging are reported. The materials studied join the properties of lanthanide (Ln(3+)) complexes and nanoparticles (NPs), offering an excellent solution for bimodal imaging. The hybrid SiO(2)@APS/DTPA:Gd:Ln (Ln = Eu(3+) or Tb(3+)) (APS: 3-aminopropyltriethoxysilane, DTPA: diethylenetriamine pentaacetic acid) system increases the payload of the active magnetic centre (Gd(3+)) and introduces a Ln(3+) long-life excited state (Eu(3+): 0.35 ± 0.02 ms, Tb(3+): 1.87 ± 0.02 ms), with resistance to photobleaching and sharp emission bands. The Eu(3+) ions reside in a single low-symmetry site. Although the photoluminescence emission is not influenced by the simultaneous presence of Gd(3+) and Eu(3+), a moderate r(1) increase and a larger enhancement of r(2) are observed, particularly at high fields, due to susceptibility effects on r(2). The presence of Tb(3+) instead of Eu(3+) further raises r(1) but decreases r(2). These values are constant over a wide (5-13) pH range, indicating the paramagnetic NPs stability and absence of leaching. The uptake of NPs by living cells is fast and results in an intensity increase in the T(1)-weighted MRI images. The optical properties of the NPs in cellular pellets are also studied, confirming their potential as bimodal imaging agents.

Synthesis, crystal structure and luminescence properties of one inorganic-organic hybrid compound [FTMA]2[Co(NCS)4] (FTMA = ferrocenylmethyltrimethylammonium cation)

A new inorganic-organic hybrid compound [FTMA](2)[Co(NCS)(4)] (FTMA = ferrocenylmethyltrimethylammonium cation) has been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Co(II) atom has a distorted tetrahedral environment with four N atoms of four NCS(-) anions. In the solid state there are C-H⋯π interactions between adjacent ferrocenyl cations, which generate one-dimensional (1-D) supramolecular chain, and C-H⋯S hydrogen bonds between [FTMA](+) cations and cobalt thiocyanate anions. The title compound shows strong purple fluorescence emission in the solid state at room temperature.

Photoluminescence as Complementary Evidence for Short-Range Order in Ionic Silica Nanoparticle Networks

Recently we published the synthesis of new hybrid materials, ionic silica nanoparticles networks (ISNN), made of silica nanoparticles covalently connected by organic bridging ligands containing imidazolium units owing to a "click-chemistry-like" reaction. Among other techniques small-angle X-ray scattering (SAXS) experiments were carried out to get a better picture of the network extension. It turned out that the short-range order in ISNN materials was strongly influenced by the rigidity of the bridging ligand, while the position of the short-range order peaks confirmed the successful linking of the bridging ligands. The photoluminescence experiments reported in this communication revealed strongly enhanced emission in the hybrid material in comparison with neat imidazolium salts. Moreover the shift of the emission maximum toward longer wavelengths, obtained when varying the aromatic ring content of the bridging ligand, suggested the existence of strong π-π stacking in the hybrid material. Experiments revealed a stronger luminescence in those samples exhibiting the higher extent of short-range order in SAXS.

Lanthanide-containing light-emitting organic-inorganic hybrids: a bet on the future

Interest in lanthanide-containing organic-inorganic hybrids has grown considerably during the last decade, with the concomitant fabrication of materials with tunable attributes offering modulated properties. The potential of these materials relies on exploiting the synergy between the intrinsic characteristics of sol-gel derived hosts (highly controlled purity, versatile shaping and patterning, excellent optical quality, easy control of the refractive index, photosensitivity, encapsulation of large amounts of isolated emitting centers protected by the host) and the luminescence features of trivalent lanthanide ions (high luminescence quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, ligand-dependent luminescence sensitization). Promising applications may be envisaged, such as light-emitting devices, active waveguides in the visible and near-IR spectral regions, active coatings, and bio-medical actuators and sensors, opening up exciting directions in materials science and related technologies with significant implications in the integration, miniaturization, and multifunctionalization of devices. This review provides an overview of the latest advances in Ln(3+)-containing siloxane-based hybrids, with emphasis on the different possible synthetic strategies, photoluminescence features, empirical determination.