Impact of ligand-centered excited states on luminescence sensitization in Pr3+ complexes with ß-diketones.

In this study, two novel Pr3+ complexes with different 1,3-diketonate ligands were synthesized and investigated. To study the effect of the ancillary ligand on the energy transfer mechanisms in the complexes, a phenanthroline ligand was introduced. To take into account the influence of the ligand environment composed of different ligands on the energy transfer and relaxation processes, we compared the synthesized compounds with a similar complex containing the phenanthroline ligand. The spectroscopic studies in the visible and near-infrared spectral regions were supplemented with DFT and TD-DFT calculations. We found two ligand-to-ligand charge transfer (LLCT) states, with one state corresponding to energy transfer between 1,3-diketones and the other - to energy transfer from the 1,3-diketone to the phenanthroline motif. It was demonstrated that optical excitation via the latter channel leads to a fourfold increase in the luminescence quantum yield as compared with excitation via the π-π∗ transitions in 1,3-diketones. Moreover, both LLCT states provide sensitization of the Pr3+ luminescence involving the 3P0 and 3P1 levels.

Effect of ancillary ligands on visible and NIR luminescence of Sm3+ß-diketonate complexes.

Two new Sm3+ complexes with pyrazolic ß-diketones bearing a CF3 group acting as main ligands and with 2,2'-bipyridine or 1,10-phenanthroline being the ancillary ligand were studied, and their energy level structure was established. Stark splitting observed in the photoluminescence spectra of the complexes points to their non-cubic symmetry, confirmed by the calculated Judd-Ofelt intensity parameters. Internal quantum yields obtained for the compounds by the Judd-Ofelt calculations were of the order of 5.5%, whereas the measured external quantum yields were 0.75% and 1.5% for Sm3+ complexes involving 2,2'-bipyridine and 1,10-phenanthroline ancillary ligands, respectively, with the corresponding sensitization efficiencies calculated as 0.16 and 0.26. It was demonstrated that replacing the 1,10-phenanthroline ancillary ligand with 2,2'-bipyridine provides an increase in the intensity of 650 nm emission of the Sm3+ complexes, with the branching ratio reaching 55%. Intensive emission of the studied complexes at 650 nm offers hope for their use as spectrally pure red emitters.

Luminescence properties of pyrazolic 1,3-diketone Ho3+ complex with 1,10-phenanthroline.

We performed spectroscopic investigations of a novel tris(1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)propane-1,3-dionato)(1,10-phenanthroline) holmium (III) complex. It was demonstrated that bonding the corresponding ligand environment to Ho3+ results in sensitization of the luminescence of the complex. The luminescence decay of the complex exhibits a biexponential behaviour. The short-lived component is attributed to the fluorescence of the ligand, whereas the long-lived component is connected with the Ho3+ emission. Using fluorescence lifetime imaging, it was shown that there is a single type of emission sites in the studied complex. Based on the results of the optical measurements, the energy diagram for the investigated Ho3+ complex was developed. It was shown that the energy transfer from the excited triplet level of the ligand environment to the 5F5 level of Ho3+ is responsible for the emission of the ion in the complex.

BODIPY dyes with thienyl- and dithienylthio-substituents - synthesis, redox and fluorescent properties.

8-Phenyl- and 8-(4-nitrophenyl)-BODIPYs with thien-2-ylthio- and (2,2'-dithien-5-yl)-thio-substitution at the 3,5-positions were synthesized. 2-Thienylthio derivatives were obtained using two different sequences, i.e., via nucleophilic substitution in the corresponding 1,9-dichlorodipyrromethenes, followed by BODIPY formation and via the same reaction using 3,5-dichloro-BODIPY dyes. The "dipyrromethene route" was observed to result in better overall yields. All the dyes were characterized by UV-Vis and fluorescence spectroscopy as well as cyclic voltammetry (CVA) studies. The UV-Vis spectra exhibited slight dependence on the thiophene chain length. The thienylthio derivatives fluoresce with modest quantum yields; conversely, no fluorescence has been detected for their dithienylthio counterparts. 8-Phenyl-3,5-di(thien-2-ylthio)-BODIPY was characterized by X-ray crystallography, which showed the layered arrangement of the molecules. The thienyl fragments of different molecules in the same layer form pairs alike H-aggregates, whereas the BODIPYs moieties in the different layers are arranged in a J-aggregate fashion. Solid fluorescence was observed for these crystals with a broad emission from 600 nm to longer than 850 nm. The CVA results correspond to those for known substituted BODIPYs except for the unusually high current observed for the oxidation process of the dithienyl derivatives with respect to the reduction process. This finding indicates oxidative film deposition.

Synthesis of novel lanthanide acylpyrazolonato ligands with long aliphatic chains and immobilization of the Tb complex on the surface of silica pre-modified via hydrophobic interactions.

Five new complexes Ln(Q(C17))3(H2O)(Solv) (Ln = Y, Solv = H2O, Ln = Tb, Dy, Sm or Eu, Solv = EtOH) were synthesized with the acylpyrazolonato ligand Q(C17) bearing a long aliphatic C17H35 chain in the acyl moiety, and the crystal structure of Y(Q(C17))3(H2O)2 shows the three aliphatic chains from the coordinated ligands positioned in the same direction, affording plane layers built by Y(Q(C17))3(H2O)2 molecules connected through H-bonding interactions. The layers are stitched to each other like in "hook & loop" tapes. Luminescence of complexes was determined and the complex Tb(Q(C17))3(H2O)(EtOH) was immobilized on the surface of silica preprocessed using a C17H35CONH(CH2)3Si(OEt)3 reagent via hydrophobic interactions of long aliphatic chains. Luminescent properties and micromorphology of the obtained hybrid particles and hybrid films were investigated. Intensive green emission of the complex retains after grafting onto the silica surface. Inclusion of the complex on the surface of silica materials occurs as separate molecules, after the disruption of the H-bonding network present in the crystalline phase of the pure terbium sample.