Synthesis, photophysical and electrochemical properties, and biological labelling studies of luminescent cyclometallated iridium(III) bipyridine-aldehyde complexes

We report the synthesis, characterisation, and photophysical and electrochemical properties of a series of luminescent cyclometallated iridium(III) bipyridine-aldehyde complexes [Ir(N-C)₂(bpy-CHO)](PF₆) (HN-C=2-phenylpyridine, Hppy (1); 2-(4-methylphenyl)pyridine, Hmppy (2); 1-phenylpyrazole, Hppz (3); 3-methyl-1-phenylpyrazole, Hmppz (4); 7,8-benzoquinoline, Hbzq (5); 2-phenylquinoline, Hpq (6); bpy-CHO=4-formyl-4^′-methyl-2,2^′-bipyridine). The X-ray crystal structures of complexes 1 and 4 have been determined. On the basis of the photophysical data, the emission of these complexes is assigned to an excited state of predominantly triplet metal-to-ligand charge-transfer (³MLCT) (dπ(Ir) → (bpy-CHO)) character. For complex 6, the excited state is also mixed with substantial (³IL) () (pq⁻) character. The protein bovine serum albumin has been labelled with these complexes to produce luminescent bioconjugates. The photophysical properties of the luminescent conjugates have also been investigated.     

Synthesis and photoluminescence properties of asymmetrical europium(III) complexes involving carbazole, phenanthroline and bathophenanthroline units

Three novel europium complexes, Eu(CCHPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H- carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](1,10-phenanthroline) europium(III), Eu(CCHPD)₃Bath = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](bathophenanthroline) europium(III) and Eu(CPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione](1,10-phenanthroline) europium(III), have been synthesized and characterized (Scheme 1). Involved ligands consist of different chelating and non-chelating units: appended carbazole (Br-Carb), phenanthroline (Phen), bathophenanthroline (Bath) and 1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione (CPD). The luminescence properties show that the carbazole moiety is a better sensitizer for the metal centred (MC) emitting states relative to Phen and Bath. Moreover, its charge-transporting properties make such complexes appealing for their application in electroluminescent devices.     

Supramolecular isomers of lanthanides(III): Synthesis, crystal structures and luminescent properties

Six lanthanide coordination polymers La₂(1,4-BDOA)₂(OX)(H₂O) (1), Ln₂(1,4-BDOA)₂(OX)(H₂O) [Ln = La (2); Ln = Pr (3); Ln = Sm (4); Ln = Eu (5); Ln = Tb (6)], [BDOA = benzene-1,4-dioxydiacetate; OX = oxalate] had been prepared under hydrothermal conditions, which were characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Compounds 1-6 crystallize in a triclinic system, space group ; compounds 1 and 2 are true structural supramolecular isomers based on BDOA ligands constructed from different acid effects; compounds 2-5 are isostructural and exhibit new 3D 12-connected topological networks, which are the same as the topological structure of 6, while 1 shows another 3D 11-connected topological architecture. Furthermore, the luminescent properties of 5 and 6 were studied.     

Synthesis, structures and luminescent properties of new heterobimetallic Zn-4f Schiff base complexes

A series of new 3d-4f heterobimetallic Schiff base complexes of the general formula [Zn(μ-L²)Ln(NO₃)₃(H₂O)_n] (Ln = La 1, Nd 2, Gd 3, Er 4 and Yb 5; n = 1 or 2; H₂L² = N,N′-bis(3-methoxy-5-p-tolylsalicylidene)ethylene-1,2-diamine) are synthesized and characterized. Complexes 1, 2, 4 and 5 are structurally characterized by X-ray crystallography. The photophysical properties of these complexes are also investigated. At room temperature, complexes 1-5 exhibit similar solution absorption and emission spectra in the UV-Vis region. Furthermore, compounds 2, 4 and 5 exhibit solution emission corresponding to the lanthanide(III) ion in the near-infrared region at room temperature. The triplet state emission of the 3d-4f bimetallic complexes without energy transfer is also determined through the photophysical study of complex 3.     

Two cadmium-thiocyanate coordination polymers with organic cations: Synthesis, crystal structures and luminescent properties

Two new inorganic-organic hybrid polymers [ClBzQl]₂[Cd(SCN)_3.5Br_0.5]·0.25H₂O (1) and [ClBzMePy][Cd(SCN)₃] (2) (ClBzQl = 1-(4′-Cl-benzyl)quinolinium cation and ClBzMePy = 1-(4′-Cl-benzyl)-2-methylpyridinium cation) have been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Crystal structure analyses show that two polymers belong to the monoclinic space group P2/n (1) and P2₁/c (2) with a = 18.548(2) Å, b = 9.526(1) Å, c = 20.689(2) Å, β = 94.008(1)°, V = 3646.6(5) Å³ for 1, and a = 11.195(2) Å, b = 16.415(3) Å, c = 10.751(2) Å, β = 102.930(3)°, V = 1925.7(7) Å³ for 2. The Cd atom exhibits a distorted octahedral coordination geometry for 1 and 2. For 1, a pair of 1,1-μ-SCN⁻ anions and a pair of 1,3-μ-SCN⁻ anions are alternately bridge adjacent Cd centers to form infinite polymeric chains. For 2, adjacent Cd atoms are linked by three 1,3-μ-SCN⁻ anions to form infinite [Cd(SCN)₃⁻]_∞ polymeric chains. The luminescent properties of the two polymers in the solid state at room temperature were investigated.     

Synthesis, crystal structure and luminescent properties of two cadmium thiocyanate coordination polymers with benzylpyridyl cations

Two luminescent Cd(II) complexes [RBzPy][Cd(SCN)₃] for R = Cl (1) and Br (2) have been synthesized and structurally characterized. The Cd atoms are all N3S3 hexa-coordinated with six bridging SCN⁻ and form infinite [Cd(SCN)₃]_∞ polymeric chains. The layer arrangement of the anionic chains was obtained using the larger halogenated benzylpyridyl cations. The luminescent properties of 1 and 2 in the solid state were investigated.     

Effects of bis(salicylidene)trimethylenediamine and 2,2′-bipyridyl on luminescence and extraction of tris(pivaloyltrifluoroacetonato)Eu(III)

The UV, excitation and luminescence spectra of EuA₃B to be the extracted species as well as the extraction of Eu(III) with pivaloyltrifluoroacetone, HA, and/or Lewis bases, B (2,2′-bipyridyl, bpy, and bis(salicylidene)trimethylenediamine, H₂saltn) into CHCl₃ were measured. The results are summarized: the stability constants of EuA₃bpy and EuA₃H₂saltn complexes are 5.85 ± 0.05 and 2.95 ± 0.06 as , respectively. The present results suggest that because of intramolecular hydrogen bonding, the stability and luminescence of the H₂saltn complex including the quantum yield are smaller than those of the bpy complex. The weaker luminescence is also concerned with the fact that the less stable complexes easily dissociate in solvents to diminish the essential concentration.     

Synthesis,characterization and luminescent properties of lanthanide complexes with an unsymmetrical tripodal ligand

Solid complexes of lanthanide nitrates with an novel unsymmetrical tripodal ligand, butyl‐N,N‐bis[(2′‐benzylaminofomyl)phenoxyl)ethyl]‐amine ( L ) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Sm(III), Eu(III), Tb(III) and Dy(III) nitrate complexes in solid state were also investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of central metal ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis, crystal structures and luminescent properties of zinc and manganese complexes from Demko-Sharpless reaction

The synthesis and crystal structure of two new complexes (Zn and Mn) containing tetrazolyl ligands are described. In situ [2+3] cycloaddition reactions of fipronil, (fipronil = (±)-5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazole-3-carbonitrile) with sodium azide in the presence of ZnCl₂ or MnCl₂ as a Lewis acid (Demko-Sharpless tetrazole synthesis method) under hydrothermal (solvothermal) reaction conditions gave [Zn(L)₂](H₂O)₂] · H₂O, 1 and [Mn(L)₂](H₂O)₂] · H₂O, 2, (HL = (±)-5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazole-3-tetrazole). The central metals in both complexes are six coordinated, which connected by two water molecules, two nitrogen atoms from different tetrazolyl groups and two nitrogen atoms from pyrazolyl rings respectively. Photoluminescence studies reveal that both title complexes exhibit strong blue fluorescent emissions at λ_max = 383 nm for 1 and 411 nm for 2 respectively in the solid state at room temperature.     

Hydrothermal synthesis, crystal structure and physical properties of a new gadolinium phosphite hydrate

A new compound Gd₄(H₂O)₅(HPO₃)₆ (1) was isolated from the reaction of gadolinium chloride GdCl₃ · nH₂O with H₃PO₃ under hydrothermal conditions. The crystal structure was solved by means of single-crystal X-ray diffraction. The structure is composed of parallel gadolinium-oxygen polyhedra chains connected by phosphite ions, and shows three-dimensional (3D) open-framework with eight-membered ring (8MR) channels. The structure is different from its counterpart Eu₂(H₂O)_2.5(PO₃H)₃ due to the effect of lanthanide contraction. The intensive intrinsic UV emission of this compound at λ_max = 312 nm comes from the spin-forbidden ⁶P_7/2 → ⁸S_7/2 f-f transition of the Gd³⁺ ions. No magnetic order was observed for this compound.     

Lipophilic phosphonium-lanthanide compounds with magnetic, luminescent, and tumor targeting properties

Multifunctional phosphonium-lanthanide compounds that simultaneously possess paramagnetism, luminescence, and tumor mitochondrial targeting properties were prepared by use of a facile method. These compounds were fully characterized by use of ¹H, ¹³C, ³¹P NMR, FT-IR, and elemental analyses. The thermal properties of these compounds including melting points and decomposition temperatures were investigated using DSC and TGA analyses. In addition, the paramagnetism, luminescence, and tumor targeting properties of these multifunctional compounds were confirmed by respective use of SQUID, fluorescence, and cell cytotoxicity studies. All compounds exhibited paramagnetism at room temperature, which could provide target delivery of these compounds to parts of the body containing tumor cells using a strong external magnetic field. In addition, these compounds display two major characteristic emissions originating from Dy^3 +, which can be utilized for imaging tumor cells. The IC₅₀ values of these compounds measured against normal breast cell line (Hs578Bst) are significantly greater than those measured against the corresponding carcinoma breast cell line (Hs578T), clearly indicating the selective tumor targeting properties of these compounds. Confocal fluorescence microscopy studies were used to confirm the yellowish-green fluorescence corresponding to the emission of dysprosium thiocyanate anion within cancer cells upon exposure of cancer cell lines such as human pancreatic carcinoma cell line (MIAPaCa-2) and human breast carcinoma (MDA-MB-231) to a solution of these phosphonium-dysprosium compounds.     

Synthesis, structure and blue luminescent properties of a new silver(I) triazolate coordination polymer with 810-a topology

A novel 3D coordination polymer [Ag(dmtrz)] (dmtrz = 3,5-dimethyl-1,2,4-triazole) (1) was prepared under solvothermal condition and structurally characterized. The crystal structure reveals that Ag(I) centers are firstly linked via dmtrz anions to form an infinite 2₁ helix, which is further interconnected to four neighboring anti-parallel helices to form a 3D framework with rare non-interpenetrating 8²10-a topology.     

Multimetallic compounds containing cyclometalated Ir(III) units: Synthesis, structure, electrochemistry and photophysical properties

The reaction of the cyclometalated Ir^III dimer [{(ppy)₂Ir}₂(μ-Cl)₂] (ppyH = 2-phenylpyridine) with silver triflate followed by a multidentate ligand [1,4-bis[3-(2-pyridyl)pyrazolylmethyl]benzene (bppb), 1,3,5-tri[3-(2-pyridyl)pyrazolylmethyl]-2,4,6-trimethylbenzene (tppb), 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2-chloro-4,6-bis(dipyridin-2-ylamino)-1,3,5-triazine (cddt) or 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (tdat)] afforded di- or trinuclear compounds: [{Ir(ppy)₂}₂(μ-bppb)](OTf)₂ (1), [{Ir(ppy)₂}₃(μ-tppb)](OTf)₃ (2), [{Ir(ppy)₂}₂(μ-tptz-OH)](OTf) (3), [{Ir(ppy)₂}₂(μ-cddt)](OTf)₂ (4) and [{Ir(ppy)₂}₂(μ-tdat)](OTf)₂ (5). All of these compounds contain cationic metal cores with corresponding triflate counter anions. The molecular structures of 1-4 reveal that the structural feature of the Ir(ppy)₂ center of the starting precursor is conserved in the products. Also, because of the nature of the ligands, there is virtually no electronic communication between the Ir^III centers except in 3 where a ring hydroxylation at the triazine carbon atom is effected upon metalation. Compounds 1-5 are robust in solution where they retain their structural integrity. The UV-Vis and emission spectra of 1-5 compounds are very similar to each other with the exception of 3 which seems to possess a different electronic structure. All the compounds are luminescent at room temperature. The emission bands indicate significant contribution from ³LC. Increase in the number of ‘Ir(ppy)₂’ units does not have any effect on emission color.     

New chelate complexes of trivalent Y and lanthanides (Eu, Ho, Yb) with a triazene N-oxide: Synthesis, structural characterization and luminescence properties

Deprotonated 3-(4-nitrophenyl)-1-phenyltriazene N-oxide reacts with YCl₃·6H₂O and LnCl₃·6H₂O (Ln = Eu, Ho, Yb) to give the monoclinic chelate complexes [Y{O₂N(C₆H₄)NNN(O)Ph}₄](Et₃NH)·H₂O (1) (Ph = C₆H₅; Et = C₂H₅) and [Ln^III{O₂N(C₆H₄)NNN(O)Ph}₄](Et₃NH)·H₂O·{CH₃OH∗} {Ln^III = Eu (2), Ho (3), Yb∗ (4), in which the metal centers present a square antiprismatic configuration. As already observed for hydrated ammonium complexes of triazene-oxides ligands with (C₆H₄)−NO₂ groups, multiple, effective O···H and N···H interactions hold the species in supramolecular 3D assemblies. The optical and the luminescent properties of the triazene-oxide europium complex 2 are also presented and fully discussed.     

Excited state properties of lanthanide complexes: Beyond ff states

Generally, metal-centered ff states dominate the discussion of the excited state properties of lanthanide complexes. In particular, the luminescence properties of Eu(III) and Tb(III) compounds have been studied in great detail for many decades. However, other types of excited states such as MC fd, MLCT, LMCT, MMCT and IL are also of interest. In this context, we have recently examined the excited state behavior of selected Ce(III), Ce(IV), Eu(II) and Gd(III) complexes which are luminescent and/or photoreactive.     

Synthesis,optical properties and cytotoxicity of meso-heteroatom substituted IR-786 analogs

Eight near-infrared heptamethine cyanines have been successfully synthesized based on IR 786 with oxygen, sulfur and amine moieties at the central position. These dyes show diverse optical properties resulting from different substitutions. Particularly, the heptamethine dyes with amine moieties have larger Stokes shifts and higher quantum yields of fluorescence. We also investigated these dyes for tumor cell cytotoxicity using cell viability and in vitro proliferation assays. Two of the compounds showed high cytotoxicity against PC-3 cancer cells.     

Fine-tuning the luminescent properties of metal-chelating 8-hydroxyquinolines through amido substituents in 5-position

New series of 5-substituted-8-hydroxyquinolines HL_n (1-6) bearing aliphatic or aromatic amido groups were synthesised. The chelating ability of these ligands toward the zinc(II) ion was tested and the photophysical characterisation of the resulting complexes (ZnL_n)₂ · 2H₂O (7-12) is reported and compared to those of the uncomplexed ligands. The photophysical data of 1-6 revealed interesting differences between aliphatic (1-3) and aromatic (4-6) amido-substituted species which, however, are no longer evident upon metal complexation. In fact while the ligands 1-3 showed a very high quantum yield (2, λ_em=470 nm; Φ=0.22) higher than that of the unsubstituted HQ compound, the ligands 4-6 displayed low quantum yield, similar to that of the complexes 7-12, which was in turn lower than that of ZnQ₂·2H₂O. The behaviour of these compounds is discussed with particular reference to the possibility of controlling the photophysical properties of such compounds through selective modification of the amido substituents.     

Synthesis and luminescent properties of the first series of lanthanide complexes based on sebacate and 2,5-pyridinedicarboxylate

By using 2,5-pyridinedicarboxylate and sebacate as rigid and flexible mixed carboxylate linkers, five new 3D lanthanide complexes, [Ln(seb)_0.5(2,5-pydc)(H₂O)] (Ln = Eu (1), Nd (2), Sm (3), Pr (4) and Tb (5), H₂pydc = 2,5-pyridinedicarboxylic acid, H₂seb = sebacate acid) with macroporous structures, have been synthesized. Complexes 1-5 were characterized by elemental analysis, ICP spectrometer and IR spectroscopy. In particular, the structures of 1-3 were further determined by single-crystal X-ray diffraction. Structural analyses reveal that complexes 1-3 have intricate 3D frameworks, which are constructed by 2,5-pyridinedicarboxylate and sebacate ligands. In addition, the thermogravimetric analysis of 1-3 and photoluminescent properties of 1 and 5 are also discussed in detail.     

Synthesis, crystal structures and luminescent properties of manganese and zinc complexes with in situ ligand formation of 3-amino-4-(5-tetrazolyl)-1H-pyrazole

Three metal-organic frameworks, [Mn(HL)(N₃)] (1), [Mn(HL)Cl(H₂O)] (2) and [Zn₂(L)₂(H₂O)] (3) where H₂L = 3-amino-4-(5-tetrazolyl)-1H-pyrazole, have been yielded through in situ hydrothermal reactions of manganese(II) or zinc(II) salts, NaN₃ and 3-amino-4-cyano-1H-pyrazole (HACP). The crystal structure analysis reveals that 1-3 have different dense 3D frameworks with Schläfli symbols of {3·4²·5²·6}{3²·4³·5⁴·6⁶} for 1 which is an unprecedented (4,6)-connected framework, {4·12²}2{4²·12⁴} for 2 which is a typical sqc519 structure, and {4²·6}2{4⁴·6²·8⁸·10} for 3 which is a typical ant/anatase structure, respectively. The ligand takes three different coordination modes in 1-3 as 3- or 4-connector. In addition, the photoluminescence of complex 3 was studied in solid state at room temperature, together with its thermal analysis.     

Synthesis, structural characterization and luminescence studies of a novel europium(III) complex [Eu(DBM)3(TPTZ)] (DBM: dibenzoylmethanate; TPTZ: 2,4,6-tri(2-pyridyl)-1,3,5-triazine)

A novel Eu(III) complex featuring three dibenzoylmethanate (DBM) ligands and a Lewis base ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) was synthesized. This novel complex was characterized by ¹H NMR, FAB-MS, and elemental analyses. The structure of the complex was established by single crystal X-ray diffraction. The nonacoordinate europium ion features six oxygen atoms of the three DBM ligands and three nitrogen atoms from the TPTZ ligand, forming a distorted monocapped square antiprism. Spectroscopic studies revealed that the electronic absorption of the complex is essentially ligand-based, while the emission is characteristic of a Eu(III) ion. It is concluded that the metal-centered red emission is promoted by the ligand-assisted energy transfer, namely the antenna effects.