Remarkable Luminescence Properties Research Articles

Synthesis and optical properties of red emitting Eu doped CaZrO3 phosphor

Eu3+ activated Ca1−xEuxZrO3 (x=0.01–0.05) phosphor with perovskite structure has been synthesized by sol–gel combustion method. The structure, morphology and optical properties of materials were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometry. The XRD results indicate that crystals of CaZrO3:Eu3+ belongs to orthorhombic perovskite structure. The phosphors can be effectively excited by UV light and the emission spectra results indicate that red luminescence of CaZrO3:Eu3+ due to electric dipole transition 5D0→7F2 at 616nm is dominant. Thus, these prepared phosphors show remarkable luminescent properties which find applications in display devices.

Preparation and bioimaging applications of AIE dye cross-linked luminescent polymeric nanoparticles.

With the ever increasing interest in biomedical applications of luminescent probes, the development of novel luminescent nanoparticles which showed high water dispersibility, strong luminescence and excellent biocompatibility has been extensively pursued. In this work, cross-linked luminescent polymeric nanoparticles based on aggregation induced emission (AIE) dyes were fabricated through combination of free radical polymerization and ring-opening reaction using AIE dye as the fluorogen and linker simultaneously. Our results demonstrated that these AIE dye based cross-inked polymeric nanoparticles showed high water dispersibility, remarkable luminescent properties and excellent biocompatibility, is highly potential for biomedical applications.

Photoluminescent red, green and blue monoliths of new Eu(III), Tb(III) and Y(III) complexes embedded in silica matrix

Large transparent photoluminescent monoliths were prepared by embedding newly synthesized Eu(III), Tb(III) and Y(III) complexes with 2-(1H-1,2,4-Triazol-3-yl)pyridine ligand in silica matrices through a modified sol-gel process. The remarkable luminescent properties of the free complexes were preserved in silica matrix, resulting in red, green and blue monoliths with a shape that may be tailored during the gelation process according to specific applications. Prior to embedment, the complexes prepared at 1/3 metal to ligand ratio were investigated through elemental analysis, thermal analysis, FT-IR, mass and fluorescence spectroscopy while the obtained silica monoliths were supplementary investigated through SEM and fluorescence spectroscopy. The emission peaks are located at 612 nm for the monolithic silica embedded Eu(III) complex, at 542 nm for the monolithic silica embedded Tb(III) complex and at 482 nm respectively for the silica monolith containing the Y(III) complex. Their excellent photoluminescent properties may recommend them as photonic conversion materials in various optoelectronic applications.

Synthesis, structural and optical properties of SrZrO3:Eu3+ phosphor

Eu3+ activated Sr1−xEuxZrO3 (x=0.01−0.04) phosphor with perovskite structure was successfully synthesized by using combustion method. The structure, morphology and optical properties of the material were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometry. The XRD results indicated that crystals of SrZrO3:Eu3+ belongs to tetragonal perovskite system. The phosphor could be effectively excited by UV light and the emission spectra results indicated that reddish-orange luminescence of SrZrO3:Eu3+ due to magnetic dipole transition 5D0→7F1 at 593 nm was dominant. Thus, the prepared phosphor showed remarkable luminescent properties which find applications in field emission display (FED) and plasma display panel (PDP) devices.

The molecular mechanism of dual emission in terpyridine transition metal complexes—ultrafast investigations of photoinduced dynamics

Temperature dependent luminescence experiments are combined with femtosecond time-resolved transient absorption spectroscopy to decipher the photoinduced excited-state relaxation pathway in mononuclear Fe, Ru and Os terpyridine complexes bearing a conjugated chromophore within the ligand framework. The herein presented complexes constitute a class of coordination compounds, which overcome the poor emission properties commonly observed for most terpyridine transition metal complexes. As reported earlier, the complexes reveal dual emission at room temperature stemming from ligand centered and metal-to-ligand charge-transfer states. The molecular mechanism of the room temperature dual luminescence is addressed experimentally in this contribution. The experimental results indicate an ultrafast branching reaction within the excited-state manifold upon photoexcitation of the ligand-centered S(1) state. This branching occurs from a "hot" excited state geometry close to the Franck-Condon point of absorption and within ∼100 fs, i.e. the temporal resolution of our experimental setup. The combination of ultrafast differential absorption experiments and temperature-dependent luminescence data allows not only to draw conclusions about the molecular mechanism underlying the observed dual emission but also to construct quantitative Jablonski diagrams and, thereby, to detail the excited-state topology determining the remarkable luminescence properties of the systems at hand.

Remarkable Luminescence Properties of Lanthanide Complexes with Asymmetric Dodecahedron Structures

The distorted coordination structures and luminescence properties of novel lanthanide complexes with oxo-linked bidentate phosphane oxide ligands--4,5-bis(diphenylphosphoryl)-9,9-dimethylxanthene (xantpo), 4,5-bis(di-tert-butylphosphoryl)-9,9-dimethylxanthene (tBu-xantpo), and bis[(2-diphenylphosphoryl)phenyl] ether (dpepo)--and low-vibrational frequency hexafluoroacetylacetonato (hfa) ligands are reported. The lanthanide complexes exhibit characteristic square antiprism and trigonal dodecahedron structures with eight-coordinated oxygen atoms. The luminescence properties of these complexes are characterized by their emission quantum yields, emission lifetimes, and their radiative and nonradiative rate constants. Lanthanide complexes with dodecahedron structures offer markedly high emission quantum yields (Eu: 55-72 %, Sm: 2.4-5.0 % in [D(6)]acetone) due to enhancement of the electric dipole transition and suppression of vibrational relaxation. These remarkable luminescence properties are elucidated in terms of their distorted coordination structures.

Role of Boron in the Polymer Chemistry and Photophysical Properties of Difluoroboron−Dibenzoylmethane Polylactide

Difluoroboron β-diketonate−polymer conjugates have remarkable solid-state luminescent properties that are useful in a variety of fields including multiphoton microscopy, cell biology, and tumor hypoxia imaging. Despite the successful applications of these systems, the role of boron in these polymeric materials has not been thoroughly investigated. Here we explore a boron-free model system with dibenzoylmethane chromophores in poly(lactic acid) (PLA) for comparison. The hydroxyl-functionalized aromatic diketone, dibenzoylmethane (dbmOH), is weakly fluorescent in the solid state and nonfluorescent in solution while its difluoroboron complex (BF2dbmOH) is highly emissive in both states. Using dbmOH and BF2dbmOH as initiators, well-defined end-functionalized polylactides, dbmPLA and BF2dbmPLA, were obtained via tin-catalyzed controlled ring-opening polymerization. Boronation of the dbmOH initiator affects the polymerization kinetics and the photophysical properties of the resulting BF2dbmPLA material. Both db...

Self‐Assembly of a Trinuclear Luminescent Europium Complex

Triangular luminescent box: Self-assembly of a new multidentate receptor with europium cations results in the formation of trinuclear discrete complexes. X-ray crystallography shows that nine-coordinate cations are linked by ligands to provide a triangular complex in the solid state and in solution. Despite the coordinated solvent molecules, this topologically unusual complex exhibits remarkable luminescent properties.

Remarkable chiral and luminescent properties of novel Yb(III) and Eu(III) complexes containing BINAPO ligand

Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors ( g = Δ ε ext/ ε max) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN) 3( S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT) 3( S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA) 3( S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN) 3( S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors ( g = Δ ε ext/ ε max) corresponding to the 7F 1 → 5D 0 transition at 590 nm is 0.091 for [Eu(TFN) 3( S-BINAPO)] and for [Yb(hfa) 3( S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the 2F 7/2 → 2F 5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT) 3( S-BINAPO)] and [Eu(TFN) 3( S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on.

N∧C∧N‐Coordinated Platinum(II) Complexes as Phosphorescent Emitters in High‐Performance Organic Light‐Emitting Devices

Abstract A series of terdentate cyclometallated PtII complexes with remarkable luminescence properties are used as new phosphorescence‐emitting dopants in a blended host matrix as the emitting layer, resulting in very high electroluminescence efficiencies. Because of the high phosphorescence quantum yields of these Pt complexes and the efficient energy transfer from both singlet and triplet excited states of the host to the emitting guest, external electroluminescence quantum efficiencies as high as 4–16 % photons per carrier and luminous efficiencies of 15–40 cd A–1 are achieved. Moreover, these high efficiency values were maintained over a four‐decade current intensity span with no significant roll‐off. Tuning of the electroluminescence spectra from the yellow to the green‐bluish region of the chromaticity diagram is obtained simply by changing the substituents at the central 5‐position of the cyclometallating ligand.

Metal Effect on the Supramolecular Structure, Photophysics, and Acid−Base Character of Trinuclear Pyrazolato Coinage Metal Complexes

Varying the coinage metal in cyclic trinuclear pyrazolate complexes is found to significantly affect the solid-state packing, photophysics, and acid-base properties. The three isoleptic compounds used in this study are [[3,5-(CF3)2Pz]M]3 with M = Cu, Ag, and Au (i.e., Cu3, Ag3, and Au3, respectively). They form isomorphous crystals and exist as trimers featuring nine-membered M3N6 rings with linear two-coordinate metal sites. On the basis of the M-N distances, the covalent radii of two-coordinate Cu(I), Ag(I), and Au(I) were estimated as 1.11, 1.34, and 1.25 angstroms, respectively. The cyclic [[3,5-(CF3)2Pz]M]3 complexes pack as infinite chains of trimers with a greater number of pairwise intertrimer M...M interactions upon proceeding to heavier coinage metals. However, the intertrimer distances are conspicuously short in Ag3 (3.204 angstroms) versus Au3 (3.885 angstroms) or Cu3 (3.813 angstroms) despite the significantly larger covalent radius of Ag(I). Remarkable luminescence properties are found for the three M3 complexes, as manifested by the appearance of multiple unstructured phosphorescence bands whose colors and lifetimes change qualitatively upon varying the coinage metal and temperature. The multiple emissions are assigned to different phosphorescent excimeric states that exhibit enhanced M...M bonding relative to the ground state. The startling luminescence thermochromic changes in crystals of each compound are related to relaxation between the different phosphorescent excimers. The trend in the lowest energy phosphorescence band follows the relative triplet energy of the three M(I) atomic ions. DFT calculations indicate that [[3,5-(R)2Pz]M]3 trimers with R = H or Me are bases with the relative basicity order Ag << Cu < Au while fluorination (R = CF3) renders even the Au trimer acidic. These predictions were substantiated experimentally by the isolation of the first acid-base adduct, [[Au3]2:toluene]infinity, in which a trinuclear Au(I) complex acts as an acid.

An alternative route to highly luminescent platinum(II) complexes: cyclometalation with N=C=N-coordinating dipyridylbenzene ligands.

The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N=C=N-coordinating ligand cyclometalated at C2 of the benzene ring ([PtL(1)Cl]), have been investigated, together with those of two new 5-substituted analogues [PtL(2)Cl] and [PtL(3)Cl] [HL(2) = methyl-3,5-di(2-pyridyl)benzoate; HL(3) = 3,5-di(2-pyridyl)toluene]. All three complexes are intense emitters in degassed solution at 298 K (lambda(max) 480-580 nm; phi(lum) = 0.60, 0.58, and 0.68 in CH(2)Cl(2)), displaying highly structured emission spectra in dilute solution, with lifetimes in the microsecond range (7.2, 8.0, and 7.8 micros). On the basis of the very small Stokes shift, the highly structured profiles, and the relatively long lifetimes, the emission is attributed to an excited state of primarily (3)pi-pi character. At concentrations >1 x 10(-)(5) M, structureless excimer emission centered at ca. 700 nm is observed. The X-ray crystal structure of [PtL(2)Cl] is also reported.

Synthesis of novel macrocyclic lanthanide chelates derived from bis-pyrazolylpyridine.

[structure: see text] New macrocyclic chelates based on bis-pyrazolylpyridine and diethylenetriaminepentaacetic acid are synthesized, and the remarkable luminescence properties of their lanthanide chelates are reported.

Photochemistry of copper(I) complexes

Copper(I) complexes with simple inorganic ligands having no acceptor orbitais of low energy ( e.g. Cl −, Br −, I −, and NH 3) are characterized by CTTS photochemistry. UV excitation of halocuprates(I) in aqueous solutions leads to the formation of a hydrated electron, which undergoes competitive recombination and scavenging reactions. The mechanism of the whole photoinduced redox process in these systems is rather medium-dependent and involves the formation and decay of hydride intermediates. Cyano (as pseudohalo) as well as mixed-ligand cyano-halo complexes of Cu(I) show similar photoredox features, demonstrating the dominance of CTTS reactivity. On the basis of their very remarkable luminescence properties, however, CTTS (or metal-centered 3d 94s 1) excited states of these coordination compounds can decay via formation of emissive intermediates, which also eject an electron. This route is interpreted by an exciplex mechanism, which apparently plays an important role in the photoinduced charge-transfer properties of the homo- and heteroleptic halocuprates(I). Cluster complexes of the type Cu 4X 4L 4 (X − = halide, L = organic amine) show remarkably rich photophysics. Multiple emissions have been observed, but excited-state assignments are somewhat ambiguous. The photochemistry of these materials has yet to be extensively studied, although some bimolecular redox reactions have been reported. Copper(I) complexes with polypyridine ligands are featured by MLCT reactivity. Formation of an exdplex (but non-emissive) via quenching of these excited states is also an essential reaction of these compounds. Differing from the CTTS character, however, they undergo photoinduced electron transfer only by means of direct redox quenching. Two-photon photochemistry is also shown by these complexes. MLCT excited states of other cationic copper(I) complexes have been involved in both intra- and inter-molecular reactions via oxidative quenching. Photocatalytic applications of Cu(I) coordination com- pounds are also demonstrated.