23 research outputs found
Self-structuring of lamellar bridged silsesquioxanes with long side spacers
Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(11)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si- (CH(2))(10)-Y(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) Cm materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils), an indication that the longer side chains in the former materials adopt gauche conformations. It has also allowed us to demonstrate for the first time that the emission features of the urea-related component of the emission of alkylene-based BSs depend critically on the length of the side spacers
Upconverting Nanoparticles Working As Primary Thermometers In Different Media
In
the past decade, noninvasive luminescent thermometry has become
popular due to the limitations of traditional contact thermometers
to operate at scales below 100 μm, as required by current demands
in disparate areas. Generally, the calibration procedure requires
an independent measurement of the temperature to convert the thermometric
parameter (usually an intensity ratio) to temperature. A new calibration
procedure is necessary whenever the thermometer operates in a different
medium. However, recording multiple calibrations is a time-consuming
task, and not always possible to perform, e.g., in living cells and
in electronic devices. Typically, a unique calibration relation is
assumed to be valid, independent of the medium, which is a bottleneck
of the secondary luminescent thermometers developed up to now. Here
we report a straightforward method to predict the temperature calibration
curve of any upconverting thermometer based on two thermally coupled
electronic levels independently of the medium, demonstrating that
these systems are intrinsically primary thermometers. SrF<sub>2</sub>:Yb/Er powder and water suspended nanoparticles were used as an illustrative
example
Metal-Free Highly Luminescent Silica Nanoparticles
Stable, cost-effective, brightly luminescent, and metal-free
organosilica
nanoparticles (NPs) were prepared using the Stöber method without
any thermal treatment above 318 K. The white-light photoluminescence
results from a convolution of the emission originated in the NH<sub>2</sub> groups of the organosilane and oxygen defects in the silica
network. The time-resolved emission spectra are red-shifted, relative
to those acquired in the steady-state regime, pointing out that the
NPs emission is governed by donor–acceptor (D<i>–</i>A) recombination mechanisms. Moreover, the increase of the corresponding
lifetime values with the monitored wavelength further supports that
the emission is governed by a recombination mechanism typical of a
D<i>–</i>A pair attributed to an exceptionally broad
inhomogeneous distribution of the emitting centers peculiar to silica-based
NPs. These NPs exhibit the highest emission quantum yield value (0.15
± 0.02) reported so far for organosilica biolabels without activator
metals. Moreover, the emission spectra and the quantum yield values
are quite stable over time showing no significant aging effects after
exposure to the ambient environment for more than 1 year, stressing
the potential of these NPs as metal-free biolabels
Photoluminescent Thermometer Based on a Phase-Transition Lanthanide Silicate with Unusual Structural Disorder
The hydrothermal synthesis of the
novel Na[LnSiO<sub>4</sub>] (Ln
= Gd, Eu, Tb) disordered orthorhombic system is reported. At 100 K,
and above, these materials are best described in the centrosymmetric
orthorhombic <i>Pnma</i> space group. At lower temperatures
(structure solved at 30 K) the unit cell changes to body-centered
with <i>Imma</i> symmetry. The materials exhibit unique
photophysical properties, arising from both, this phase transformation,
and the disorder of the Ln<sup>3+</sup> ions, located at a site with <i>D</i><sub><i>2d</i></sub> point symmetry. Na[(Gd<sub>0.8</sub>Eu<sub>0.1</sub>Tb<sub>0.1</sub>)SiO<sub>4</sub>] is an
unprecedented case of a luminescent ratiometric thermometer based
on a very stable silicate matrix. Moreover, it is the first example
of an optical thermometer whose performance (viz., excellent sensitivity
at cryogenic temperatures <100 K) is determined mainly by a structural
transition, opening up new opportunities for designing such devices
Deciphering Density Fluctuations in the Hydration Water of Brownian Nanoparticles via Upconversion Thermometry
We investigate the intricate relationship among temperature,
pH,
and Brownian velocity in a range of differently sized upconversion
nanoparticles (UCNPs) dispersed in water. These UCNPs, acting as nanorulers,
offer insights into assessing the relative proportion of high-density
and low-density liquid in the surrounding hydration water. The study
reveals a size-dependent reduction in the onset temperature of liquid-water
fluctuations, indicating an augmented presence of high-density liquid
domains at the nanoparticle surfaces. The observed upper-temperature
threshold is consistent with a hypothetical phase diagram of water,
validating the two-state model. Moreover, an increase in pH disrupts
the organization of water molecules, similar to external pressure
effects, allowing simulation of the effects of temperature and pressure
on hydrogen bonding networks. The findings underscore the significance
of the surface of suspended nanoparticles for understanding high-
to low-density liquid fluctuations and water behavior at charged interfaces
Ratiometric Nanothermometer Based on an Emissive Ln<sup>3+</sup>-Organic Framework
Luminescent thermometers working at the nanoscale with high spatial resolution, where the conventional methods are ineffective, have emerged over the last couple of years as a very active field of research. Lanthanide-based materials are among the most versatile thermal probes used in luminescent nanothermometers. Here, nanorods of metal organic framework Tb<sub>0.99</sub>Eu<sub>0.01</sub>(BDC)<sub>1.5</sub>(H<sub>2</sub>O)<sub>2</sub> (BDC = 1-4-benzendicarboxylate) have been prepared by the reverse microemulsion technique and characterized and their photoluminescence properties studied from room temperature to 318 K. Aqueous suspensions of these nanoparticles display an excellent performance as ratiometric luminescent nanothermometers in the physiological temperature (300–320 K) range
Photoluminescent Lanthanide-Organic Framework Based on a Tetraphosphonic Acid Linker
A new
metal–organic framework based on the highly flexible
tetraphosphonic acid linker hexamethylenediamine-<i>N,N,N</i>′<i>,N</i>′-tetrakis(methylphosphonic acid)
(H<sub>8</sub>htp) is reported. [Ln<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>(H<sub>6</sub>htp)(H<sub>2</sub>O)<sub>4</sub>]·10H<sub>2</sub>O [Ln<sup>3+</sup>= Eu<sup>3+</sup> (<b>1</b>), Sm<sup>3+</sup> (<b>2</b>), and Gd<sup>3+</sup> (<b>3</b>)]
was readily obtained by microwave heating at moderate temperatures
(80 °C) and low reaction time (15 min). The reaction was carried
out in aqueous medium and, because of the high flexibility of the
organic linker, sulfuric acid was added in small quantities. This
acid delays the coordination process and blocks access of the phosphonic
acid groups by coordinating the sulfate anion to the metal center,
leading to the formation of a compact 3D network. Sulfuric acid further
proved to be crucial for the formation of the materials because the
use of different acids led to either no precipitation or amorphous
compounds. When compared to the only known and reported material based
on the same building blocks, this approach allowed us to significantly
reduce the reaction time to just 15 min with an immediate crystal
formation (compared to the 2 months reported). Crystals were obtained
with sizes suitable for single-crystal X-ray diffraction analysis
for <b>1</b>. Materials consist of a 3D network with the metal
centers forming a close packed layer, being interconnected by the
organic linker, forming cavities which are filled with solvent water
molecules. Topologically, <b>1</b>–<b>3</b> are
binodal networks with a 4,8-connectivity and a Schäfli point
symbol of {4<sup>12</sup>·6<sup>12</sup>·8<sup>4</sup>}{4<sup>6</sup>}<sub>2</sub>. This topology is unusual for MOFs, especially
for phosphonic acid based linkers, resembling the known mineral fluorite.
The photoluminescence properties of <b>1</b> were studied showing
an emission lifetime of 0.43 ± 0.01 ms and 0.57 ± 0.01 at
297 and 13 K, respectively
Deciphering Density Fluctuations in the Hydration Water of Brownian Nanoparticles via Upconversion Thermometry
We investigate the intricate relationship among temperature,
pH,
and Brownian velocity in a range of differently sized upconversion
nanoparticles (UCNPs) dispersed in water. These UCNPs, acting as nanorulers,
offer insights into assessing the relative proportion of high-density
and low-density liquid in the surrounding hydration water. The study
reveals a size-dependent reduction in the onset temperature of liquid-water
fluctuations, indicating an augmented presence of high-density liquid
domains at the nanoparticle surfaces. The observed upper-temperature
threshold is consistent with a hypothetical phase diagram of water,
validating the two-state model. Moreover, an increase in pH disrupts
the organization of water molecules, similar to external pressure
effects, allowing simulation of the effects of temperature and pressure
on hydrogen bonding networks. The findings underscore the significance
of the surface of suspended nanoparticles for understanding high-
to low-density liquid fluctuations and water behavior at charged interfaces
Lamellar Salt-Doped Hybrids with Two Reversible Order/Disorder Phase Transitions
A lamellar bilayer hierarchically
structured amide cross-linked
alkyl/siloxane hybrid matrix (mono-amidosil, m-A(14)) was doped with
a wide concentration range of potassium triflate (KCF<sub>3</sub>SO<sub>3</sub>), magnesium triflate (Mg(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>), and europium triflate (Eu(CF<sub>3</sub>SO<sub>3</sub>)<sub>3</sub>). In the K<sup>+</sup>-, Mg<sup>2+</sup>-, and Eu<sup>3+</sup>-based samples with <i>n</i> ≥ 5, 20, and 60 (where <i>n</i> is the molar ratio of amide CO groups per cation),
respectively, the original lamellar structure of m-A(14) coexists
with a new lamellar phase with lower interlamellar distance. The texture
of the mono-amidosils doped with K<sup>+</sup>, Mg<sup>2+</sup>, and
Eu<sup>3+</sup> ions mimics cabbage leaves, foliated schist, and sea
sponges, respectively. In the three series of materials, the cations
bond to the oxygen atoms of the amide carbonyl groups. The amide–amide
hydrogen-bonded array of m-A(14) is less perturbed by the inclusion
of KCF<sub>3</sub>SO<sub>3</sub> and Mg(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> than by the incorporation of Eu(CF<sub>3</sub>SO<sub>3</sub>)<sub>3</sub>. The degree of ionic association is low for <i>n</i> ≥ 20. The cations coordinate to the oxygen atoms
of the triflate ions, forming contact ion pairs at higher salt content.
In the Mg(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>- and Eu(CF<sub>3</sub>SO<sub>3</sub>)<sub>3</sub>-containing materials with <i>n</i> = 5 and 10, respectively, crystalline salt is formed.
The structural changes undergone by the alkyl chains of selected mono-amidosils
in a heating/cooling cycle are reversible, are time-independent, and
exhibit two distinct hysteresis domains, one associated with the order/disorder
phase transition of the original lamellar bilayer structure of m-A(14)
and the second one associated with the order/disorder phase transition
of the new lamellar bilayer structure formed in the presence of the
salts