Multifunctional Platform Based on a Copper(I) Complex and NaYF4:Tm3+,Yb3+ Upconverting Nanoparticles Immobilized into a Polystyrene Matrix: Downshifting and Upconversion Oxygen Sensing.

This work presents an innovative approach to obtain a multifunctional hybrid material operating via combined anti-Stokes (upconversion) and Stokes (downshifting) emissions for oxygen gas sensing and related functionalities. The material is based on a Cu(I) complex exhibiting thermally activated delayed fluorescence emission (TADF) and infrared-to-visible upconverting Tm3+/Yb3+-doped NaYF4 nanoparticles supported in a polystyrene (PS) matrix. Excitation of the hybrid material at 980 nm leads to efficient transfer of Tm3+ emission in the ultraviolet/blue region to the Cu(I) complex and consequently intense green emission (560 nm) of the latter. Additionally, the green emission of the complex can also be directly generated with excitation at 360 nm. Independently of the excitation wavelength, the emission intensity is efficiently suppressed by the presence of molecular oxygen and the quenching rate is properly characterized by the Stern-Volmer plots. The results indicate that the biocompatible hybrid material can be applied as an efficient O2 sensor operating via near-infrared or ultraviolet excitation, unlike most optical oxygen sensors currently available which only work in downshifting mode.

Mesoporous silica nanoparticles incorporated with Ir(III) complexes: From photophysics to photodynamic therapy.

Organically modified mesoporous silica nanoparticles (MSNs) containing Ir complexes (Ir1, Ir2 and Ir3) were successfully synthesized. These Ir-entrapped MCM41-COOH nanoparticles have shown relevant photophysical characteristics including high efficiency in the photoproduction and delivery of singlet oxygen (1O2), which is particularly promising for photodynamic therapy (PDT) applications. In vitro tests have evidenced that complex@MCM41-COOH are able to reduce cell proliferation after 10 min of blue-light irradiation in Hep-G2 liver cancer cells.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices.

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

Visible-Light-Mediated Photodynamic Water Disinfection @ Bimetallic-Doped Hybrid Clay Nanocomposites.

This study reports a new class of photocatalytic hybrid clay nanocomposites prepared from low-cost sources (kaolinite clay and Carica papaya seeds) doped with Zn and Cu salts via a solvothermal process. X-ray diffraction analysis suggests that Cu-doping and Cu/Zn-doping introduce new phases into the crystalline structure of Kaolinite clay, which is linked to the reduced band gap of kaolinite from typically between 4.9 and 8.2 eV to 2.69 eV for Cu-doped and 1.5 eV for Cu/Zn hybrid clay nanocomposites (Nisar, J.; Århammar, C.; Jämstorp, E.; Ahuja, R. Phys. Rev. B 2011, 84, 075120). In the presence of solar light irradiation, Cu- and Cu/Zn-doped nanocomposites facilitate the electron-hole pair separation. This promotes the generation of singlet oxygen which in turn improves the water disinfection efficiencies of these novel nanocomposite materials. The nanocomposite materials were further characterized using high-resolution scanning electron microscopy, fluorimetry, thermogravimetric analysis, and Raman spectroscopy. The breakthrough times of the nanocomposites for a fixed bed mode of disinfection of water contaminated with 2.32 × 107 cfu/mL E. coli ATCC 25922 under solar light irradiation are 25 h for Zn-doped, 30 h for Cu-doped, and 35 h for Cu/Zn-doped nanocomposites. In the presence of multidrug and multimetal resistant strains of E. coli, the breakthrough time decreases significantly. Zn-only doped nanocomposites are not photocatalytically active. In the absence of light, the nanocomposites are still effective in decontaminating water, although less efficient than under solar light irradiation. Electrostatic interaction, metal toxicity, and release of singlet oxygen (only in the Cu-doped and Cu/Zn-doped nanocomposites) are the three disinfection mechanisms by which these nanocomposites disinfect water. A regrowth study indicates the absence of any living E. coli cells in treated water even after 4 days. These data and the long hydraulic times (under gravity) exhibited by these nanocomposites during photodisinfection of water indicate an unusually high potential of these nanocomposites as efficient, affordable, and sustainable point-of-use systems for the disinfection of water in developing countries.

Photophysical Properties of Ir(III) Complexes Immobilized in MCM-41 via Templated Synthesis.

In the search for understanding and improving the luminescence of optical materials based on Ir(III) complexes, three [Ir(C∧N)2(dnbp)]+ (dnbp = 4,4'-dinonyl-2,2'-bipyridine) emitters were immobilized in MCM-41 mesoporous nanoparticles. By taking advantage of the amphiphilic nature of [Ir(C∧N)2(dnbp)]+, the complexes were mixed with an appropriate surfactant and the resulting micelles served as templates for the synthesis of mesoporous silica host materials in a one-step sol-gel route. The MCM-encapsulated [Ir(C∧N)2(dnbp)]+ complexes present intense emissions with prominent rigidochromic spectral changes that are substantially less affected by O2 as compared to methanolic solutions, with a thousand-fold decrease in quenching rate constants. These photophysical results points to a possible suitability of Ir(III)-complex-MCM-41 host-guest systems for possible future optoelectronic devices, rigidity optical sensors, or biological markers in different colors.

Host-guest luminescent materials based on highly emissive species loaded into versatile sol-gel hosts.

Sol-gel chemistry has been extensively employed to produce several classes of materials (e.g. nanoparticles, thin films, fibers, gels, glasses and ceramic powders) with desired easily-controllable morphological, crystallographic and mechanical properties. In particular, the methodology can be explored for the development of optical supramolecular materials with interesting properties for light-emitting devices, chemical and biological sensing, biomarking and targeting, among many others. To this end, the strategies usually adopted consist of embedding a luminescent guest species into normally non-emissive sol-gel host materials, resulting in optical systems that preserve both the guest's photophysical characteristics and the host's mechanical and morphological properties. This concise review provides insights into the development of promising new host-guest optical materials based on versatile sol-gel hosts (i.e. mesoporous MCM-41 nanoparticles, mesoporous sodium-aluminosilicate glasses and other mesoporous matrices for sensors) and highly luminescent guests (i.e. organic dyes, d6 complexes and lanthanide complexes), mostly focusing on the findings from our group and similar findings in the literature of the past decade.

Reaching Biocompatibility with Nanoclays: Eliminating the Cytotoxicity of Ir(III) Complexes.

Cyclometalated IrIII complexes are promising candidates for biomedical applications but high cytotoxicity limits their use as imaging and sensing agents. We herein introduce the use of Laponite as carrier for triplet-emitting cyclometalated IrIII complexes. Laponite is a versatile nanoplatform because of its biocompatibility, dispersion stability and large surface area that readily adsorbs functional nonpolar and cationic molecules. These inorganic-organic hybrid nanomaterials mask cytotoxicity, show efficient cell uptake and increase luminescent properties and photostability. By camouflaging intrinsic cytotoxicity, this simple method potentially extends the palette of available imaging and sensing dyes to any metal-organic complexes, especially those that are usually cytotoxic.

Photophysical dynamics of the efficient emission and photosensitization of [Ir(pqi)2(NN)]+ complexes.

The photophysical dynamics of three complexes in the highly-emissive [Ir(pqi)2(NN)]+ series were investigated aiming at unique photophysical features and applications in light-emitting and singlet oxygen sensitizing research fields. Rational elucidation and Franck-Condon analyses of the observed emission spectra in nitrile solutions at 298 and 77 K reveal the true emissive nature of the lowest-lying triplet excited state (T1), consisting of a hybrid 3MLCT/LCIr(pqi)→pqi state. Emissive deactivations from T1 occur mainly by very intense, yellow-orange phosphorescence with high quantum yields and radiative rates. The emission nature experimentally verified is corroborated by theoretical calculations (TD-DFT), with T1 arising from a mixing of several transitions induced by the spin-orbit coupling, majorly ascribed to 3MLCT/LCIr(pqi)→pqi and increasing contributions of 3MLCT/LLCTIr(pqi)→NN. The microsecond-lived emission of T1 is rapidly quenched by molecular oxygen, with an efficient generation of singlet oxygen. Our findings show that the photophysics of [Ir(pqi)2(NN)][PF6] complexes is suitable for many applications, from the active layer of electroluminescent devices to photosensitizers for photodynamic therapy and theranostics.

Functionalizing the Mesoporous Silica Shell of Upconversion Nanoparticles To Enhance Bacterial Targeting and Killing via Photosensitizer-Induced Antimicrobial Photodynamic Therapy.

Core-shell nanoparticles operating by infrared-to-visible energy upconversion (UCNPs) have been proposed as theranostic carriers for photosensitizers to increase deep-tissue penetration of photodynamic therapy against tumors and bacterial infections. Herein we present a series of core-shell mesoporous silica-coated NaYF4:Yb:Er UCNPs (mSiO2@UCNP) with different surface functionalizations to enhance bacterial targeting and loaded with the hydrophobic photosensitizer SiPc (silicon 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine dihydroxide) to boost the bactericidal effect against Gram-positive and Gram-negative bacteria upon near-infrared irradiation. Förster resonance energy transfer (FRET) from the UCNP core to loaded SiPc was facilitated, while its efficiency depended on UCNP shell functionalization, which influences the SiPc penetration depth into the mesoporous silica, constituting a convenient tool to modify FRET intensity. Functionalized UCNPs displayed dark toxicity toward Gram-negative E. coli of up to 5 orders of magnitude, while Gram-positive S. aureus viability was not decreased in the dark, offering practical means for discriminating between the two bacterial strains. Directly exciting SiPc on the UNCP led to complete eradication of E. coli and a drastic decrease of colony-forming units of S. aureus of up to 7 orders of magnitude. With this study, we demonstrate strategies to potentiate antimicrobial photodynamic therapy on nanoparticular structures that can lead to next-generation photosensitizing systems based on UCNPs to help encounter and eradicate resistant bacteria, as well as for theranostics and future in vivo applications.

New complexes of Cu(II) with dipicolinate and pyridyl-based ligands: An experimental and DFT approach.

The three novel mononuclear copper(II) complexes with dipicolinate and pyridyl-based ligands [Cu(dipic)(L)(OH2)] (L=4-picoline, vinylpyridine, 4-styrylpyridine; dipic2-=dipicolinate) were afforded and structurally characterized. X-ray diffraction studies accounted for slight distorted square-pyramidal structures in which the dianion dipic2- acts as a tridentate ligand in a mer-fashion, the N-donor species occupy an in-plane position, and a water molecule was detected apically coordinated. To assess the effect of the nature of the pyridyl-substituent (para position) on electronic properties, other complexes were also synthesized: [Cu(dipic)(py)(OH2)], [{Cu(dipic)(OH2)}2(µ-pyz)] and [{Cu(dipic)(OH2)}(µ-pypy){Cu(dipic)}] (py=pyridine, pyz=pyrazine, pypy=(E)-1,2-bis(pyridine-4-yl)ethane). Absorptive behavior in the UV-VIS region was studied in solution and in the solid state (reflectance measurements). Additionally, geometry and population analyses were conducted by means of DFT calculations. Electronic UV-VIS spectra were simulated for both dinuclear complexes in the framework of the TD-DFT methodology to assign the origin of the absorption bands.

The polynuclear complex Cu4I4py4 loaded in mesoporous silica: photophysics, theoretical investigation, and highly sensitive oxygen sensing application.

The polynuclear complex Cu4I4py4 has been largely studied in solution and in the powder form due to its interesting luminescent properties, which are largely dependent on temperature and pressure. In this work, we present the synthesis of the complex and its wet impregnation in a mesoporous silica host obtained by sol-gel methodology. For optimized loadings, the well-dispersed guest molecules exhibit strong interaction with molecular oxygen, resulting in a significant quenching of the luminescence. The process is highly reversible with a Stern-Volmer constant of Ksv = 33.8, which is the largest value found in the literature for similar complexes in the solid state, suggesting that the new material is a promising candidate for high sensitivity oxygen sensing. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations reveal a weak intermolecular interaction between the two guest complexes in the excited state, suggesting the formation of an excited state complex (excimer). The assumption of a triplet excimer formation is confirmed by temperature- and concentration-dependent experiments, which provides a new way to explain the giant Stokes shift observed for the guest complex in different media.

Structural models for yttrium aluminium borate laser glasses: NMR and EPR studies of the system (Y2O3)(0.2)-(Al2O3)x-(B2O3)(0.8-x).

The structure of laser glasses in the system (Y(2)O(3))(0.2){(Al(2)O(3))(x))(B(2)O(3))(0.8-x)} (0.15 ≤ x ≤ 0.40) has been investigated by means of (11)B, (27)Al, and (89)Y solid state NMR as well as electron spin echo envelope modulation (ESEEM) of Yb-doped samples. The latter technique has been applied for the first time to an aluminoborate glass system. (11)B magic-angle spinning (MAS)-NMR spectra reveal that, while the majority of the boron atoms are three-coordinated over the entire composition region, the fraction of three-coordinated boron atoms increases significantly with increasing x. Charge balance considerations as well as (11)B NMR lineshape analyses suggest that the dominant borate species are predominantly singly charged metaborate (BO(2/2)O(-)), doubly charged pyroborate (BO(1/2)(O(-))(2)), and (at x = 0.40) triply charged orthoborate groups. As x increases along this series, the average anionic charge per trigonal borate group increases from 1.38 to 2.91. (27)Al MAS-NMR spectra show that the alumina species are present in the coordination states four, five and six, and the fraction of four-coordinated Al increases markedly with increasing x. All of the Al coordination states are in intimate contact with both the three- and the four-coordinate boron species and vice versa, as indicated by (11)B/(27)Al rotational echo double resonance (REDOR) data. These results are consistent with the formation of a homogeneous, non-segregated glass structure. (89)Y solid state NMR spectra show a significant chemical shift trend, reflecting that the second coordination sphere becomes increasingly "aluminate-like" with increasing x. This conclusion is supported by electron spin echo envelope modulation (ESEEM) data of Yb-doped glasses, which indicate that both borate and aluminate species participate in the medium range structure of the rare-earth ions, consistent with a random spatial distribution of the glass components.

Structural ordering in Cd(x)Pb(1-x)F2 alloys: a combined molecular dynamics and solid state NMR study.

Molecular dynamics (MD) simulations of binary Cd(x)Pb(1-x)F(2) alloys have been carried out, using a two-body Buckingham interaction potential, leading to a correct description of structural properties as a function of composition and pointing towards an understanding of the eutectic phenomenon. The simulation data can be analyzed in terms of five local fluorine environments Q((n)) (4> or =n> or =0), where n is the number of Pb nearest-neighbor environments. The results suggest a highly nonstatistical population distribution, suggesting an intrinsic phase segregation tendency in the undercooled melt, during the cooling process. This prediction has been tested experimentally for six representative compositions (0.2< or =x< or =0.7) on the basis of high-resolution (19)F solid state NMR data, revealing important similarities between theory and experiment. While the NMR data confirm that the population distribution is, indeed, nonstatistical for all compositions, the results are only found to be consistent with an intrinsic segregation tendency of PbF(2)-rich domains. This tendency manifests itself in substatistical populations of Q((3)) units, resulting in preferred Q((2)) and Q((4)) formations.

Excited-state absorption and 1064-nm end-pumped laser emission of Nd:YVO4 single-crystal fiber grown by laser-heated pedestal growth.

We present an investigation of the excited-state absorption and laser emission of a 1.0-at. %-Nd3+-doped YVO4 single-crystal fiber grown by the low-cost and versatile laser-heated pedestal growth technique. Efficient laser emission at 1064 nm was achieved when the fiber was pumped, in an end-pump cavity, by a Ti:sapphire laser at 808 nm. A continuous-wave threshold of 10 mW was observed with an efficiency of 42% with respect to the absorbed pump power and the maximum output power of 200 mW. These results are excellent when compared with those of a commercial bulk crystal adapted to the same cavity (48% efficiency, 250-mW maximum output power). Thus the fibers are characterized as strong candidates for the construction of compact lasers that can also be pumped by low-cost diode lasers.