Circularly Polarized Luminescence from Pure and Eu-Doped Trigonal TbPO4·nH2O Nanocrystals.

In this contribution, we describe the preparation, by means of a precipitation reaction from aqueous solution at 40 °C, and the structural characterization of nanocrystalline powders of trigonal Tb1-xEuxPO4·nH2O (with x = 0, 0.005, 0.01, 0.05, and 0.1; n tentatively assigned as 0.67) which crystallize in the two possible P3121 or P3221 enantiomorphic space groups. While the volume of the crystal lattice is not significantly affected by the Tb3+/Eu3+ substitution, the average crystallite size seems to depend on the Eu3+ dopant concentration and ranges from 13 to 30 nm. The desired handedness of the crystals has been induced by using, during the synthesis, one of the two possible enantiomers of tartaric acid (l or d). The analysis of the luminescence excitation and emission spectra, together with the decay kinetics of the 5D4 Tb3+ excited state, suggests the presence of a very efficient Tb3+ → Eu3+ energy transfer process in the Eu3+-doped orthophosphates. Upon excitation of Tb3+ ions at 368 nm, the enantiomorphic powders grown with l- or d-tartaric acid (i.e., l-TbPO4·0.67H2O/d-TbPO4·0.67H2O, l-Tb0.995Eu0.005PO4·0.67H2O/d-Tb0.995Eu0.005PO4·0.67H2O, and l-Tb0.9Eu0.1PO4·0.67H2O/d-Tb0.9Eu0.1PO4·0.67H2O) exhibited mirror circularly polarized luminescence signals in the visible spectral region (in the green and/or in the red).

Circularly Polarized Luminescence from New Heteroleptic Eu(III) and Tb(III) Complexes.

The complexes [Eu(bpcd)(tta)], [Eu(bpcd)(Coum)], and [Tb(bpcd)(Coum)] [tta = 2-thenoyltrifluoroacetyl-acetonate, Coum = 3-acetyl-4-hydroxy-coumarin, and bpcd = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetate] have been synthesized and characterized from photophysical and thermodynamic points of view. The optical and chiroptical properties of these complexes, such as the total luminescence, decay curves of the Ln(III) luminescence, electronic circular dichroism, and circularly polarized luminescence, have been investigated. Interestingly, the number of coordinated solvent (methanol) molecules is sensitive to the nature of the metal ion. This number, estimated by spectroscopy, is >1 for Eu(III)-based complexes and <1 for Tb(III)-based complexes. A possible explanation for this behavior is provided via the study of the minimum energy structure obtained by density functional theory (DFT) calculations on the model complexes of the diamagnetic Y(III) and La(III) counterparts [Y(bpcd)(tta)], [Y(bpcd)(Coum)], and [La(bpcd)(Coum)]. By time-dependent DFT calculations, estimation of donor-acceptor (D-A) distances and of the energy position of the S1 and T1 ligand excited states involved in the antenna effect was possible. These data are useful for rationalizing the different sensitization efficiencies (ηsens) of the antennae toward Eu(III) and Tb(III). The tta ligand is an optimal antenna for sensitizing Eu(III) luminescence, while the Coum ligand sensitizes better Tb(III) luminescence {ϕovl = 55%; ηsens ≥ 55% for the [Tb(bpcd)(Coum)] complex}. Finally, for the [Eu(bpcd)(tta)] complex, a sizable value of glum (0.26) and a good quantum yield (26%) were measured.

Ln(III) Complexes Embedded in Biocompatible PLGA Nanoparticles as Potential Vis-to-NIR Optical Probes.

In this contribution, we present the spectroscopic study of two NIR emitting hydrophobic heteroleptic (R,R)-YbL1(tta) and (R,R)-NdL1(tta) complexes (with tta = 2-thenoyltrifluoroacetonate and L1 = N,N'-bis(2-(8-hydroxyquinolinate)methylidene)-1,2-(R,R or S,S)-cyclohexanediamine), both in methanol solution and embedded in water dispersible and biocompatible poly lactic-co-glycolic acid (PLGA) nanoparticles. Thanks to their absorption properties in a wide range of wavelengths extending from the UV up to the blue and green visible regions, the emission of these complexes can be effectively sensitized using visible radiation, which is much less harmful to tissues and skin than the UV one. The encapsulation of the two Ln(III)-based complexes in PLGA allows us to preserve their nature, making them stable in water and to test their cytotoxicity on two different cell lines, with the aim of using them in the future as potential bioimaging optical probes.

Dynamics of the Energy Transfer Process in Eu(III) Complexes Containing Polydentate Ligands Based on Pyridine, Quinoline, and Isoquinoline as Chromophoric Antennae.

In this work, we investigated from a theoretical point of view the dynamics of the energy transfer process from the ligand to Eu(III) ion for 12 isomeric species originating from six different complexes differing by nature of the ligand and the total charge. The cationic complexes present the general formula [Eu(L)(H2O)2]+ (where L = bpcd2- = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate; bQcd2- = N,N'-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate; and bisoQcd2- = N,N'-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate), while the neutral complexes present the Eu(L)(H2O)2 formula (where L = PyC3A3- = N-picolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetate; QC3A3- = N-quinolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetate; and isoQC3A3- = N-isoquinolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetate). Time-dependent density functional theory (TD-DFT) calculations provided the energy of the ligand excited donor states, distances between donor and acceptor orbitals involved in the energy transfer mechanism (RL), spin-orbit coupling matrix elements, and excited-state reorganization energies. The intramolecular energy transfer (IET) rates for both singlet-triplet intersystem crossing and ligand-to-metal (and vice versa) involving a multitude of ligand and Eu(III) levels and the theoretical overall quantum yields (ϕovl) were calculated (the latter for the first time without the introduction of experimental parameters). This was achieved using a blend of DFT, Judd-Ofelt theory, IET theory, and rate equation modeling. Thanks to this study, for each isomeric species, the most efficient IET process feeding the Eu(III) excited state, its related physical mechanism (exchange interaction), and the reasons for a better or worse overall energy transfer efficiency (ηsens) in the different complexes were determined. The spectroscopically measured ϕovl values are in good agreement with the ones obtained theoretically in this work.

Regreening properties of the soil slow-mobile H2bpcd/Fe3+ complex: Steps forward to the development of a new environmentally friendly Fe fertilizer.

The application of synthetic Fe-chelates stands for the most established agronomical practice to alleviate lime-induced chlorosis, which still constitutes a major agronomic problem. However, the percolation through the soil profile due to the negative charge of the most deployed molecules results in agronomical and environmental problems. H2bpcd/Fe3+ complex features distinctive chemical characteristics, including moderate stability of the Fe(bpcd)+ species (logß ML = 20.86) and a total positive charge, and we studied its behavior in soil and regreening effects on cucumber plants. Soil column experiments have underlined that H2bpcd/Fe3+ is retained in more amounts than EDDHA/Fe3+. The new ligand was not proven to be toxic for the cucumber and maize seedlings. A concentration of 20 µM H2bpcd/Fe3+ attained regreening of Fe-deficient cucumber plants grown in the hydroponic solution supplied with CaCO3, similar to that shown by EDDHA/Fe3+. Experiments with a 2 µM concentration of 57Fe showed that cucumber roots absorbed H2bpcd/57Fe3+ at a slower rate than EDTA/57Fe3+. The high kinetic inertness of H2bpcd/Fe3+ may explain such behavior.

Near Infared Circularly Polarized Luminescence From Water Stable Organic Nanoparticles Containing a Chiral Yb(III) Complex.

We report the first example of very efficient NIR Circularly Polarized Luminescence (CPL) (around 970 nm) in water, obtained thanks to the combined use of a chiral Yb complex and of poly lactic-co-glycolic acid (PLGA) nanoparticles. [YbL(tta)2 ]CH3 COO (L=N, N'-bis(2-pyridylmethylidene)-1,2-(R,R+S,S) cyclohexanediamine and tta=2-thenoyltrifluoroacetonate) shows good CPL in organic solvents, because the tta ligands efficiently sensitize Yb NIR luminescence and the readily prepared chiral ligand L endows the complex with the necessary dissymmetry. PLGA nanoparticles incorporate the complex and protect the metal ion from the intrusion of solvent molecules, while ensuring biocompatibility, water solubility and stability to the complex. Hydrophilic NIR-CPL optical probes can find applications in the field of NIR-CPL bio-assays.

Systematic Analysis of the Crystal Chemistry and Eu3+ Spectroscopy along the Series of Double Perovskites Ca2LnSbO6 (Ln = La, Eu, Gd, Lu, and Y).

Eu3+ (1 mol %)-doped Ca2LnSbO6 (replacing Ln3+; Ln = Lu, Y, Gd, and La) and Ca2EuSbO6 were synthesized and structurally characterized by means of X-ray powder diffraction. The Eu3+ luminescence spectroscopy of the doped samples and of Ca2EuSbO6 has been carefully investigated upon collection of the excitation/emission spectra and luminescence decay curves of the main excited states. Surprisingly, apart from the dominant red emission from 5D0, all the doped samples show an uncommon blue and green emission contribution from 5DJ (J = 1, 2, and 3). This is made possible thanks to both multiphonon and cross-relaxation mechanism inefficiencies. However, the emission from 5D3 is more efficient and the decay kinetics of the 5DJ (J = 0, 1, and 2) levels is slower in the case of Y- and Lu-based doped samples. This evidence can find a possible explanation in the crystal chemistry of this family of double perovskites: our structural investigation suggests an uneven distribution of the Eu3+ dopant ions in Ca2YSbO6 and Ca2LuSbO6 hosts of the general A2BB'O6 formula. The luminescent center is mainly located in the A crystal site, and on average, the Eu-Eu distances are longer than in the case of the Gd- and La-based matrix. These longer distances can further reduce the efficiency of the cross-relaxation mechanism and, consequently, the radiative transitions are more efficient. The slower depopulation of Eu3+ 5D2 and 5D1 levels in Ca2YSbO6 and Ca2LuSbO6 hosts is reflected in the longer rise observed in the 5D1 and 5D0 decay curves, respectively. Finally, in Ca2EuSbO6, the high Eu3+ concentration gives rise to an efficient cross-relaxation within the subset of the lanthanide ions so that no emission from 5DJ (J = 1, 2, and 3) is possible and the 5D0 decay kinetics is faster than for the doped samples.

Isoquinoline-based Eu(iii) luminescent probes for citrate sensing in complex matrix.

A neutral Eu(iii) complex containing the S,S enantiomer of isoQC3A3- ligand (isoQC3A3- = N-isoquinolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) was synthesized and characterized. The complex was spectroscopically investigated and the results compared with those obtained for the similar bis-anionic ligand bisoQcd2- (bisoQcd2- = N,N'-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate). Both Eu(iii)-complexes show similar binding constants upon titration with the main analytes contained in interstitial extracellular fluid (i.e. hydrogen carbonate, serum albumin and citrate). However, the analyte affinity is accompanied by different enhancements of the Eu(iii) intrinsic quantum yield (QY). Structures and hydration numbers of the complexes are determined by luminescence decay measurements and DFT calculations. The QYs as well as the binding constants of the individual adducts of the complexes with hydrogen carbonate, bovine serum albumin (BSA) and citrate are determined. The study of the Eu(iii) emission upon the systematic variation of one analyte in a complex mixture has been carried out to predict the performance of the luminescent sensor in conditions close to the real extracellular environment. Both Eu(iii) complexes can detect citrate at extracellular concentrations up to 500 µM, even at millimolar concentrations of the other interfering species. In the case of the Eu(bisoQcd)OTf complex, an increase of 23% of the Eu(iii) luminescence intensity at 615 nm upon addition of 0.3 mM of citrate was recorded. This feature makes the latter complex a viable probe for luminescence analysis of citrate in a complex matrix.

Templated-Construction of Hollow MoS2 Architectures with Improved Photoresponses.

Despite the outstanding optoelectronic properties of MoS2 and its analogues, synthesis of such materials with desired features including fewer layers, arbitrary hollow structures, and particularly specifically customized morphologies, via inorganic reactions has always been challenging. Herein, using predesigned lanthanide-doped upconversion luminescent materials (e.g., NaYF4:Ln) as templates, arbitrary MoS2 hollow structures with precisely defined morphologies, widely variable dimensions, and very small shell thickness (≈2.5 nm) are readily constructed. Most importantly, integration of the near-infrared-responsive template significantly improves the photoresponse of up to 600 fold in device made of NaYF4:Yb/Er@MoS2 compared with that of MoS2 nanosheets under 980 nm laser illumination. Multichannel optoelectronic device is further fabricated by simply changing luminescent ions in the template, e.g., NaYF4:Er@MoS2, operating at 1532 nm light excitation with a 276-fold photoresponse enhancement. The simple chemistry, easy operation, high reliability, variable morphologies, and wide universality represent the most important advantages of this novel strategy that has not been accessed before.

Effect of the Heteroaromatic Antenna on the Binding of Chiral Eu(III) Complexes to Bovine Serum Albumin.

The cationic enantiopure (R,R) and luminescent Eu(III) complex [Eu(bisoQcd)(H2O)2] OTf (with bisoQcd = N,N'-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate and OTf = triflate) was synthesized and characterized. At physiological pH, the 1:1 [Eu(bisoQcd)(H2O)2]+ species, possessing two water molecules in the inner coordination sphere, is largely dominant. The interaction with bovine serum albumin (BSA) was studied by means of several experimental techniques, such as luminescence spectroscopy, isothermal titration calorimetry (ITC), molecular docking (MD), and molecular dynamics simulations (MDS). In this direction, a ligand competition study was also performed by using three clinically established drugs (i.e., ibuprofen, warfarin, and digitoxin). The nature of this interaction is strongly affected by the type of the involved heteroaromatic antenna in the Eu(III) complexes. In fact, the presence of isoquinoline rings drives the corresponding complex toward the protein superficial area containing the tryptophan residue 134 (Trp134). As the main consequence, the metal center undergoes the loss of one water molecule upon interaction with the side chain of a glutamic acid residue. On the other hand, the similar complex containing pyridine rings ([Eu(bpcd)(H2O)2]Cl with bpcd = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate) interacts more weakly with the protein in a different superficial cavity, without losing the coordinated water molecules.

Effect of the Counterion on Circularly Polarized Luminescence of Europium(III) and Samarium(III) Complexes.

Each enantiopure europium(III) and samarium(III) nitrate and triflate complex of the ligand L, with L = N,N'-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine ([LnL(tta)2]·NO3 and [LnL(tta)2(H2O)]·CF3SO3, where tta = 2-thenoyltrifluoroacetylacetonate) has been synthesized and characterized from a spectroscopic point of view, using a chiroptical technique such as electronic circular dichroism (ECD) and circularly polarized luminescence (CPL). In all cases, both ligands are capable of sensitizing the luminescence of both metal ions upon absorption of light around 280 and 350 nm. Despite small differences in the total luminescence (TL) and ECD spectra, the CPL activity of the complexes is strongly influenced by a concurrent effect of the solvent and counterion. This particularly applies to europium(III) complexes where the CPL spectra in acetonitrile can be described as a weighed linear combination of the CPL spectra in dichloromethane and methanol, which show nearly opposite signatures when their ligand stereochemistries are the same. This phenomenon could be related to the presence of equilibria interconverting solvated, anion-coordinated complexes and isomers differing by the relative orientation of the tta ligands. The difference between some bond lengths (M-N bonds, in particular) in the different species could be at the basis of such an unusual CPL activity.

Eu(iii) and Tb(iii) complexes of 6-fold coordinating ligands showing high affinity for the hydrogen carbonate ion: a spectroscopic and thermodynamic study.

In the present contribution, four classes of Ln(iii) complexes (Ln = Eu and Tb) have been synthesized and characterized in aqueous solution. They differ by charge, Ln(bpcd)+ [bpcd2- = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate] and Ln(bQcd)+ (bQcd2- = N,N'-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate) being positively charged and Ln(PyC3A) (PyC3A3- = N-picolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) and Ln(QC3A) (QC3A3- = N-quinolyl-N,N',N'-trans-l,2-cyclohexylenediaminetriacetate) being neutral. Combined DFT, spectrophotometric and potentiometric studies reveal the presence, under physiological conditions (pH 7.4), of a couple of equally and highly stable isomers differing by the stereochemistry of the ligands (trans-N,N and trans-O,O for bpcd2- and bQcd2-; trans-O,O and trans-N,O for PyC3A3- and QC3A3-). Their high log ß values (9.97 < log ß < 15.68), the presence of an efficient antenna effect and the strong increase of the Ln(iii) luminescence intensity as a function of the hydrogen carbonate concentration in physiological solution, render these complexes as very promising optical probes for a selective detection of HCO3-in cellulo or in extracellular fluid. This particularly applies to the cationic Eu(bpcd)+, Tb(bpcd)+ and Eu(bQcd)+ complexes, which are capable of guesting up to two hydrogen carbonate anions in the inner coordination sphere of the metal ion, so that they show an unprecedented affinity towards HCO3- (log K for the formation of the adduct in the 4.6-5.9 range).

Circularly Polarized Luminescence from an Eu(III) Complex Based on 2-Thenoyltrifluoroacetyl-acetonate and a Tetradentate Chiral Ligand.

A new chiral complex {[EuL(tta)2(H2O)]CF3SO3; L = N, N'-bis(2-pyridylmethylidene)-1,2-( R, R + S, S)-cyclohexanediamine; tta = 2-thenoyltrifluoroacetyl-acetonate} has been synthesized and characterized from a structural and spectroscopic point of view. The molecular structure in the solid state shows the presence of one chiral L, two tta, and one water molecules bound to the metal center. L and tta molecules can efficiently harvest and transfer to Eu(III) the UV light absorbed in the 250-400 nm range. The forced electric-dipole 5D0 → 7F2 emission band dominates the Eu(III) emission spectra recorded in the solid state and in solution of acetonitrile or methanol and the calculated intrinsic quantum yield of the metal ion is around 40-50%. The light emitted by the enantiopure complex shows a sizable degree of polarization with a maximum value of the emission dissymmetry factor ( glum) equal to 0.2 in methanol solution. If compared with the complex in the solid state or in acetonitrile solution, then the first coordination sphere of Eu(III) when the complex is dissolved in methanol is characterized by the presence of one CH3OH molecule instead of water. This fact is related to different Eu(III) CPL signatures in the two solvents.

Disorder-Induced Breaking of the Local Inversion Symmetry in Rhombohedral Pyrochlores M2La3Sb3O14 (M = Mg or Ca): A Structural and Spectroscopic Investigation.

A detailed investigation of the overall crystal structure, and in particular of the local structure around the cations in M2La3Sb3O14 (M = Mg, Ca) was accomplished using X-ray diffraction, steady state luminescence spectroscopy and decay kinetics, and state of the art density functional calculations. The computational tool was also used to investigate the structure of Mn2La3Sb3O14. The Eu3+ dopant ion was employed as an optical probe of the local symmetry at the cationic sites. The use of these complementary techniques shows that the antimonates under investigation belong to the rhombohedral pyrochlore family with space group R3̅ m (No. 166), but while Mg2La3Sb3O14 and Mn2La3Sb3O14 show an ordered cationic configuration, the Ca2+ and La3+ of Ca2La3Sb3O14 are disordered because of their similar ionic radii. In both the Mg- and the Ca-based compounds, the Eu3+ ions formally occupy centrosymmetric sites, but in the case of Ca2La3Sb3O14 the presence of disorder in the outer coordination spheres removes the local inversion symmetry in these sites. This has a strong influence on the Eu3+ luminescence spectrum and on the radiative decay rate of the 5D0 emitting level.

Vanadium(v) oxoanions in basic water solution: a simple oxidative system for the one pot selective conversion of l-proline to pyrroline-2-carboxylate.

The unprecedented, direct chemical oxidation of l-proline to pyrroline-2-carboxylate was achieved in water (pH 9-10) by means of NH4VO3/NH3 or V2O5/MOH (K = Na, K), and the anion was fully characterized as ammonium or alkaline metal salts. Quantitative yield and higher atom economy performance were achieved with the latter system, the alkaline salts being more stable than the ammonium one. Different mixed valence V(iv)/V(v) compounds precipitated from the reaction mixtures depending on the nature of the employed base. A possible reaction mechanism is proposed according to DFT calculations. The analogous reaction of trans-4-hydroxy-l-proline with NH4VO3/NH3 afforded pyrrole-2-carboxylic acid in 81% yield, while sarcosine underwent prevalent decomposition under similar experimental conditions. Instead, no reaction was observed with primary (glycine, l-alanine, l-phenylalanine) and tertiary α-amino acids (N,N-dimethyl-l-phenylalanine, N,N-dimethylglycine).

Strongly Circularly Polarized Emission from Water-Soluble Eu(III)- and Tb(III)-Based Complexes: A Structural and Spectroscopic Study.

Water-soluble Eu(III) and Tb(III) complexes with N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (H2bpcd) have been synthesized and characterized in their racemic and enantiopure forms. The ligand has been designed to bind Ln(III) ions, providing a dissymmetric environment able to solicit strong chiroptical features while at the same time leaving a few coordination sites available for engaging further ancillary ligands. Potentiometric studies show that Ln(III) complexes have a relatively good stability and that at pH 7 the [Ln(bpcd)]+ species is largely dominant. DFT calculations carried out on the (S,S)-[Y(bpcd)(H2O)5]+ complexes (the closed-shell equivalents of [Eu(bpcd)(H2O)5]+ and [Tb(bpcd)(H2O)5]+) indicate that the two trans-O,O and trans-Npy,Npy configurations are equally stable in solution and present two coordinated water molecules. This is in agreement with the hydration number ∼2.6 determined by luminescence lifetime measurements on Tb(III) and Eu(III) complexes. A detailed optical and chiroptical spectroscopic characterization has been carried out and reveals that the complexes display an efficient luminescence in the visible spectral range accompanied by a strong CPL activity. A value for glum (around 0.1 on the top of the 546 nm band) for the Tb-based complex has been found. This is one of the highest glum values measured up to now for chiral Tb complexes. These results suggest that in principle Tb(bpcd)Cl is suitable to be employed as a CPL bioprobe for relevant analytes in aqueous media.

Synthesis of a highly reactive form of WO2Cl2, its conversion into nanocrystalline mono-hydrated WO3 and coordination compounds with tetramethylurea.

A new form of WO2Cl2 was obtained by modification of a literature procedure. Both the newly prepared WO2Cl2 and the commercial yellow WO2Cl2 exhibited an orthorhombic structure (powder X-ray diffraction, P-XRD), and their air exposure at room temperature afforded light green and lemon yellow WO3·H2O (orthorhombic phase), respectively. These materials were characterized by P-XRD, high-resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (S-TEM). The analyses revealed the nanocrystalline nature of light green WO3·H2O, and the prevalent amorphism of lemon yellow WO3·H2O. The reactions of grey WO2Cl2 with one and two equivalents of tetramethylurea (tmu), in CH2Cl2 at room temperature, led to the isolation of the trinuclear complex [WO2Cl2(tmu)]3, 1 (45% yield), and the mononuclear one WO2Cl2(tmu)2, 2 (64%), respectively. Compounds 1 and 2 were fully characterized by analytical and spectroscopic methods, single crystal X-ray diffraction (SC-XRD) and DFT calculations.

Synthesis of Nanocrystalline TiOF2 Embedded in a Carbonaceous Matrix from TiF4 and D-Fructose.

Nanostructured titanium oxide difluoride embedded in a matrix of amorphous carbon was synthesized by pyrolysis of D-fructose in the presence of titanium tetrafluoride (optimal Ti/fructose molar ratio = 5.5), both in the solid state at ca. 150 °C and in suspension of 1,2-dichloroethane at reflux temperature. The resulting solid materials were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and elemental analysis. In every case, PXRD and TEM data indicated the presence of an unique crystalline phase (TiOF2) embedded in a light matrix (amorphous carbon). The average crystal size of the powder can be regulated by varying the reaction time.

Tuning of the sensing properties of luminescent Eu(3+) complexes towards the nitrate anion.

A new family of imine-based ligands containing pyridine or furan as an aromatic donating ring [N,N'-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine, L1; N,N'-bis(2-furanylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine, L2 and N,N'-bis(2-thienylmethylidene)-1,2-(R,S)-cyclohexanediamine, L3] has been prepared in high yield by means of an easy synthetic protocol. Their trifluoromethansulphonate (CF3SO3(-), OTf(-)) Eu(iii) complexes have been employed for luminescence sensing of the NO3(-) anion in an anhydrous acetonitrile solution. Spectrophotometric titrations have been carried out to define the speciation in the solution and study the formation of ternary species occurring with the addition of NO3(-) anions. The sensing response towards this anion is strongly dependent on the nature of the ligand, the stoichiometry of the complexes and their concentration.

Structural, optical and sensing properties of novel Eu(III) complexes with furan- and pyridine-based ligands.

A new family of imine and amine-based racemic ligands containing furan or pyridine as an aromatic donating ring [N,N'-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine, L1; N,N'-bis(2-furanylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine, L2; N,N'-bis(2-pyridylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine, L3; and N,N'-bis(2-furanylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine, L4] and their trifluoromethanesulphonate (CF3SO3(−), OTf(−)) and nitrate Eu(III) complexes is studied in acetonitrile (AN) solution. The stoichiometry and stabilities of the formed complexes are obtained by means of spectrophotometric titrations: when Eu(III) triflate is used as a starting salt, two mononuclear species (1:1 and 1:2) are detected, while only the 1:1 complex is observed when the nitrate salt is employed. The stability of these complexes, as well as the geometry of their Eu(III) environment, is significantly dependent on the nature of the ligand employed (imine or amine, furan or pyridine-based). DFT calculations show that all donor atoms are coordinated to the metal ion in the 1:1 EuL(L = L1­L4) species and suggest that the higher stability of the complexes with L1 and L2 with respect to L3 and L4 is mostly due to the higher degree of preorganization of the former species. The optical response of the imine-based L1 and L2 Eu complexes, produced by NO3(−) coordination, has been studied in order to assess their application as sensing devices. With both ligands, an increase of the emission intensity on the addition of the nitrate ion is observed. This is higher for the EuL2 complex and underlines the important role of the nature of the heteroaromatic ring. Finally, it is worth noting that an efficient energy transfer process from the ligand to the metal is present in the case of the 1:1 triflate Eu(III) complex with the ligand L1.