Biological labelling reagents and probes derived from luminescent transition metal polypyridine complexes

Fluorescence of new o-carborane compounds with different fluorophores: can it be tuned?

Two sets of o-carborane derivatives incorporating fluorene and anthracene fragments as fluorophore groups have been successfully synthesized and characterized, and their photophysical properties studied. The first set, comprising fluorene-containing carboranes 6-9, was prepared by catalyzed hydrosilylation reactions of ethynylfluorene with appropriate carboranylsilanes. The compound 1-[(9,9-dioctyl-fluorene-2-yl)ethynyl]carborane (11) was synthesized by the reaction of 9,9-dioctyl-2-ethynylfluorene and decaborane (B10H14). Furthermore, reactions of the lithium salt of 11 with 1 equivalent of 4-(chloromethyl)styrene or 9-(chloromethyl)anthracene yielded compounds 12 and 13. Members of the second set of derivatives, comprising anthracene-containing carboranes, were synthesized by reactions of monolithium or dilithium salts of 1-Me-1,2-C2B10H11, 1-Ph-1,2-C2B10H11, and 1,2-C2B10H12 with 1 or 2 equivalents of 9-(chloromethyl)anthracene, respectively, to produce compounds 14-16. In addition, 2 equivalents of the monolithium salts of 1-Me-1,2-C2B10H11 (Me-o-carborane) and 1-Ph-1,2-C2B10H11 (Ph-o-carborane) were reacted with 9,10-bis(chloromethyl)anthracene to produce compounds 17 and 18, respectively. Fluorene derivatives 6-9 exhibit moderate fluorescence quantum yields (32-44 %), whereas 11-13, in which the fluorophore is bonded to the Ccluster (Cc), show very low emission intensity (6 %) or complete fluorescence quenching. The anthracenyl derivatives containing the Me-o-carborane moiety exhibit notably high fluorescence emissions, with ϕF = 82 and 94 %, whereas their Ph-o-carborane analogues are not fluorescent at all. For these compounds, we have observed a correlation between the Cc-Cc bond length and the fluorescence intensity in CH2Cl2 solution, comparable to that observed for previously reported styrene-containing carboranes. Thus, our hypothesis is that for systems of this type the fluorescence may be tuned and even predicted by changing the substituent on the adjacent Cc.

Modulation of the organelle specificity in Re(i) tetrazolato complexes leads to labeling of lipid droplets

Neutral Re(i) tetrazolato complexes exhibit labeling of lipid droplets with high specificity.

Photophysical behaviour of cyclometalated iridium(III) complexes with phosphino(terthiophene) ligands

Six new Ir(III) complexes containing the 3'-phosphino-2,2':5',2''-terthiophene (PT3) ligand in three different coordination modes are reported. The electronic properties of the complexes are characterized by cyclic voltammetry, absorption, emission and time-resolved transient absorption spectroscopies and DFT/TDDFT calculations. The electrochemical and photophysical behaviour of the complexes was found to be dominated by the PT3 ligand. For the complexes in which the PT3 ligand is coordinated in a bidentate P,S or P,C mode, the lowest energy absorption band is attributed to π-π* PT3 localized transitions consistent with observations from DFT calculations. Emission quantum yields are low in all cases (<0.07) and emission lifetimes are short (<50 ns). Intersystem crossing leads to a long-lived triplet state ((3)L) also localized on the PT3 group. In the complex where the PT3 ligand is coordinated only via the phosphine, TDDFT calculations suggest that there is some MLCT (and Cl-PT3 CT) character in the lowest energy transition.

Phosphorescent imaging of living cells using a cyclometalated iridium (III) complex

A cell permeable cyclometalated iridium(III) complex has been developed as a phosphorescent probe for cell imaging. The iridium(III) solvato complex [Ir(phq)₂(H₂O]₂)] preferentially stains the cytoplasm of both live and dead cells with a bright luminescence.

Syntheses, crystal structure and luminescent properties of cadmium complexes based on 2,6-bis(1-phenylbenzimidazol-2-yl)pyridine

Two cadmium complexes, Cd(bpbp)Cl(2) (complex 1) and [Cd(bpbp)(2)](ClO(4))(2) (complex 2), based on 2,6-bis(1-phenylbenzimidazol-2-yl)pyridine (bpbp), were synthesized and characterized by X-ray single crystal structure analyses. For complex 1: crystal system, monoclinic, space group, C2/c, a=27.427(3)Å, b=13.4495(15)Å, c=14.8381(17)Å, β=106.635(2)°, V=5244.4(10)Å(3), Z=8. It is a neutral complex. The Cd(II) ion distorted trigonal bipyramidal geometry is five-coordinated by three nitrogen atoms from ligand (bpbp) and two chlorine ions. For complex 2: crystal system, triclinic, space group, P-1, a=13.4791(15)Å, b=13.8506(16)Å, c=16.5839(19)Å, α=94.202(2)°, β=106.948(2)°, γ=94.872(2)°, V=2935.3(6)Å(3), Z=2. It is an ionic complex. The Cd(II) ion octahedral geometry is six-coordinated by six nitrogen atoms from two ligand (bpbp). Both complexes emit blue luminescence with emission peaks at 420 and 430 nm in solid state and with emission peaks at 415 and 425 nm in DMF solution. In complex 1 absorption spectra, there is not only the free ligand absorption peak at 310 nm, but also shows strong Cd-Cl charge transfer peak at 350 nm in DMF solution.

Determination of the relative ligand-binding strengths in heteroleptic Ir(III) complexes by ESI-Q-TOF tandem mass spectrometry

An electrospray ionization quadrupole time-of-flight mass spectrometer has been utilized to investigate the relative ligand-binding strengths in a series of heteroleptic-charged iridium(III) complexes of the general formula [(C^N)(2) Ir(III) (S-tpy)](PF(6) ) by using variable collision energies. Collision-induced dissociation experiments were performed in order to study the stability of the Ir(III) complexes that are, for instance, suitable phosphors in light-emitting electrochemical cells. The ratio of signal intensities belonging to the fragment and the undissociated complex depends on the collision energy applied for the tandem mass spectra (MS/MS) analysis. By defining the threshold collision energy and the point of complete complex dissociation, it is possible to estimate the relative complex stabilities depending on the nature of the coordinated ligands [i.e. type of cyclometalating ligand (C^N), substituents on the S-shaped terpyridine (S-tpy)]. The collision energy values differed as a function of the coordination sphere of the Ir(III) centers.

Synthesis and characterization of new fluorescent styrene-containing carborane derivatives: the singular quenching role of a phenyl substituent

A set of neutral and anionic carborane derivatives in which the styrenyl fragment is introduced as a fluorophore group has been successfully synthesized and characterized. The reaction of the monolithium salts of 1-Ph-1,2-C(2)B(10)H(11), 1-Me-1,2-C(2)B(10)H(11) and 1,2-C(2)B(10)H(12) with one equivalent of 4-vinylbenzyl chloride leads to the formation of compounds 1-3, whereas the reaction of the dilithium salt of 1,2-C(2)B(10)H(12) with two equivalents of 4-vinylbenzyl chloride gives disubstituted compound 4. The closo clusters were degraded using the classical method, KOH in EtOH, to afford the corresponding nido species, which were isolated as tetramethylammonium salts. The crystal structure of the four closo compounds 1-4 were analyzed by X-ray diffraction. All compounds, except 1, display emission properties, with quantum yields dependent on the nature of the cluster (closo or nido) and the substituent on the second C(cluster) atom. In general, closo compounds 2-4 exhibit high fluorescence emission, whereas the presence of a nido cluster produces a decrease of the emission intensity. The presence of a phenyl group bonded to the C(cluster) results in an excellent electron-acceptor unit that produces a quenching of the fluorescence. DFT calculations have confirmed the charge-separation state in 1 to explain the quenching of the fluorescence and the key role of the carboranyl fragment in this luminescent process.

Synthesis, properties, and live-cell imaging studies of luminescent cyclometalated iridium(III) polypyridine complexes containing two or three biotin pendants

Three luminescent cyclometalated iridium(III) bis-biotin complexes [Ir(N(wedge)C)(2)(N(wedge)N)](PF(6)) (HN(wedge)C = 2-(4-(N-(6-(biotinamido)hexyl)aminomethyl)phenyl)pyridine, HppyC6B, N(wedge)N = 2,2'-bipyridine, bpy (1); HN(wedge)C = 2-phenylpyridine, Hppy, N(wedge)N = 4,4'-bis((2-(biotinamido)ethyl)aminocarbonyl)-2,2'-bipyridine, bpyC2B2 (2); HN(wedge)C = Hppy, N(wedge)N = 4,4'-bis((2-((6-(biotinamido)hexanoyl)amino)ethyl)aminocarbonyl)-2,2'-bipyridine, bpyC2C6B2 (3)) and one tris-biotin complex [Ir(ppyC6B)(2)(bpyC6B)](PF(6)) (bpyC6B = 4-((6-(biotinamido)hexyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine) (4) have been synthesized and characterized. The biotin-free complex [Ir(ppy)(2)(bpyC4)](PF(6)) (bpyC4 = 4,4'-bis(n-butylaminocarbonyl)-2,2'-bipyridine) (5) has also been prepared for comparison studies. Upon photoexcitation, all the complexes displayed intense and long-lived greenish-yellow to red triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi (Ir) --> pi*(N(wedge)N)) emission in fluid solutions at room temperature and in low-temperature glass. Cyclic voltammetric studies revealed iridium(IV/III) oxidation at about +1.21 to + 1.29 V and diimine-based reductions at about -1.07 to -1.39 V versus SCE. The interactions of the bis-biotin and tris-biotin complexes with avidin have been studied by 4'-hydroxyazobenzene-2-carboxylic acid (HABA) assays, emission titrations, and dissociation assays. The possibility of these complexes as cross-linkers for avidin has been examined by microscopy studies using avidin-conjugated green fluororescent microspheres and size-exclusion HPLC analysis. Utilization of these luminescent iridium(III) biotin complexes in signal amplification has been demonstrated using avidin-coated nonfluorescent microspheres and complex 3 as an example. Additionally, the lipophilicity of all the complexes has been determined by reversed-phase HPLC. The cytotoxicity of these iridium(III) complexes toward the human cervix epithelioid carcinoma (HeLa) cell line has been evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assays. Furthermore, the cellular uptake of the complexes has been examined by ICP-MS, laser-scanning confocal microscopy, and flow cytometry.

Excellent photostability of phosphorescent nanoparticles and their application as a color converter in light emitting diodes

The phosphorescent Ir(III) complexes were modified by allylation and consecutive hydrosilylation, and covalently incorporated into the silica nanoparticles by hydrolysis and condensation reaction with TEOS. These nanoparticles showed an excellent photochemical and thermal stability, and a very high luminescent efficiency due to the blocking of O(2) quenching and suppression of energy transfer through the amorphous silica solid solution. The limited mobility of complexes in the silica matrix also resulted in a decrease in the vibration relaxation and restrained the nonradiative decay. It is expected that these photostable and very efficient phosphorescent nanoparticles can be used in various fields ranging from nanobiotechnology to nanoengineering materials, where long-term stability with the high luminescent efficiency is required. As an example of the use of excellent photostability, a preliminary test result in which they are used as a color converter in a light emitting diode (LED) is also discussed.