Sensitized luminescence from lanthanides in d–f bimetallic complexes

Design of a dual Ir-Eu tag for fluorescent visualization and ICP-MS quantification of SIRPα and its host cells

With the expansion of ICP-MS application into the field of bioanalysis, there is an urgent need for novel element tags today. Here, we report the design of a dual-element Ir-Eu tag, opening the door to simultaneous fluorescent imaging and ICP-MS quantification. The ratio of 153Eu/193Ir may serve as a precision control of the labeling process, allowing internal validation of the quantitative results obtained. As for SIRPα and its host cell analysis exemplified here, the Ir-Eu tag demonstrated superior figures of ICP-MS quantification with the LOD (3σ) down to 0.5 (153Eu) and 1.1 (193Ir) pM SIRPα and 220 (153Eu) and 830 (193Ir) RAW264.7 cells more than 130 times more sensitive compared with the LOD (3σ) of 65.2 pM SIRPα at 612 nm using fluorometry. Not limited to these demonstrations, we believe that the design ideas of the dual Ir-Eu tags should be applicable to various cases of bioanalysis when dual optical profiling and ICP-MS quantification are indispensable.

Ratiometric Luminescent Thermometer Based on the Lanthanide Metal-Organic Frameworks by Thermal Curing

The high-performance optical thermometer probes are of great significance in diverse areas; lanthanide metal-organic frameworks (Ln-MOFs) are a promising candidate for luminescence temperature sensing owing to their unique luminescence properties. However, Ln-MOFs have poor maneuverability and stability in complex environments due to the crystallization properties, which then hinder their application scope. In this work, the Tb-MOFs@TGIC composite was successfully prepared using simple covalent crosslinking through uncoordinated -NH₂ or COOH on Tb-MOFs reacting with the epoxy groups on TGIC {Tb-MOFs = [Tb₂(atpt)₃(phen)₂(H₂O)]_n; H₂atpt = 2-aminoterephthalic acid; phen = 1,10-phenanthroline monohydrate}. After curing, the fluorescence properties, quantum yield, lifetime, and thermal stability of Tb-MOFs@TGIC were remarkably enhanced. Meanwhile, the obtained Tb-MOFs@TGIC composites exhibit excellent temperature sensing properties in the low-temperature (S_r = 6.17% K^-1 at 237 K), physiological temperature (S_r = 4.86% K^-1 at 323 K), or high-temperature range (S_r = 3.88% K^-1 at 393 K) with high sensitivity. In the temperature sensing process, the sensing mode of single emission changed into double emission for ratiometric thermometry owing to the back energy transfer (BenT) from Tb-MOFs to TGIC linkers, and the BenT process enhanced with the increase of temperature, which further improved the accuracy and sensitivity of temperature sensing. Most notably, the temperature-sensing Tb-MOFs@TGIC can be easily coated on the surface of polyimide (PI), glass plate, silicon pellet (SI), and poly(tetrafluoroethylene) plate (PTFE) substrates by a simple spraying method, which also exhibited an excellent sensing property, making it applicable for a wider T range measurement. This is the first example of a postsynthetic Ln-MOF hybrid thermometer operative over a wide temperature range including the physiological and high temperature based on back energy transfer.

4f → 3d sensitization: a luminescent EuII-MnII heteronuclear complex with a near-unity quantum yield

A new heteronuclear Eu^II-Mn^II complex [Eu(N2O6)]MnBr4 (N2O6 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) is designed and synthesized, which shows an intense green emission from Mn^II with a near-unity photoluminescence quantum yield. Measurement of excited-state dynamics demonstrated the sensitization process from Eu^II to Mn^II, which represents the first example of f → d molecular sensitization. Due to the large optical absorption cross-section of the Eu^II center, [Eu(N2O6)]MnBr4 shows an emission intensity 7 to 2500 times stronger than that of the Sr^II-Mn^II control complex [Sr(N2O6)]MnBr4 upon the excitation of near ultraviolet to blue light.

Lanthanide(III)-Cu4 I4 Organic Framework Scintillators Sensitized by Cluster-Based Antenna for High-Resolution X-ray Imaging

Scintillator-based X-ray imaging has attracted great attention from industrial quality inspection and security to medical diagnostics. Herein, a series of lanthanide(III)-Cu₄ I₄ heterometallic organic frameworks (Ln-Cu₄ I₄ MOFs)-based X-ray scintillators are developed by rationally assembling X-ray absorption centers ([Cu₄ I₄ ] clusters) and luminescent chromophores (Ln(III) ions) in a specific manner. Under X-ray irradiation, the heavy inorganic units ([Cu₄ I₄ ] clusters) absorb the X-ray energy to populate triplet excitons via halide-to-ligand charge transfer (XLCT) combined with the metal-to-ligand charge-transfer (MLCT) state (defined as the X/MLCT state), and then the ³ X/MLCT excited state sensitizes Tb³⁺ for intense X-ray-excited luminescence via excitation energy transfer. The obtained Tb-Cu₄ I₄ MOF scintillators exhibit high resistance to humidity and radiation, excellent linear response to X-ray dose rate, and high X-ray relative light yield of 29 379 ± 3000 photons MeV^-1 . The relative light yield of Tb-Cu₄ I₄ MOFs is ≈3 times higher than that of the control Tb(III) complex. X-ray imaging tests show that the Tb-Cu₄ I₄ MOFs-based flexible scintillator film exhibits a high spatial resolution of 12.6 lp mm^-1 . These findings not only provide a promising design strategy to develop lanthanide-MOF-based scintillators with excellent scintillation performance, but also exhibit high-resolution X-ray imaging for biological specimens and electronic chips.

Enhancing the Luminescence of Eu(III) Complexes with the Ruthenocene Organometallic Unit as Ancillary Ligand

Five novel Eu(III)-β-diketonate complexes containing ruthenocene ancillary ligands (1,1'-bis(diphenylphosphoryl)ruthenocene─RcBPO) were synthesized and characterized. The coordination compounds presented the general formula [Eu(β-dik)₃(RcBPO)], where β-dik stands for 2-thenoyltrifluoroacetonate (tta), 3-benzoyl-1,1,1-trifluoroacetone (btf), 2-dibenzoylmethanate (dbm), 2-acetyl-1,3-indandionate (aind), and 2-benzoyl-1,3-indandionate (bind), and RcBPO stands for 1,1'-bis(diphenylphosphoryl)ruthenocene. The [Eu(aind)₃(RcBPO)] complex crystallizes in a monoclinic Cc non-centrosymmetric space group with the europium site environment, assuming a bicapped trigonal prism coordination polyhedron with the symmetry point group close to C_2v. Photoluminescent properties for the solid-state samples were described in terms of excitation, emission, lifetime decay curves, and intrinsic and overall quantum yields. The replacement of the two coordinated H₂O molecules by the RcBPO ancillary ligand leads to great enhancements of the overall quantum yields (Q_Eu^L), with the minimum increment by a factor of 5 for the case of [Eu(btf)₃(RcBPO)] and the maximum enhancement of 270 times for the case of the [Eu(dbm)₃(RcBPO)] complex. In addition, theoretical calculations were carried out to model the spectroscopic properties of the investigated compounds. To obtain theoretical Judd-Ofelt parameters (Ω_λ, λ = 2, 4, and 6) and intramolecular energy transfer rates, the JOYSpectra web platform was employed using the structure obtained from density functional theory calculations. Hence, a rate equation model provided theoretical overall quantum yields, which are in great agreement with measured data.

Heteroleptic mer-[Cr(N∩N∩N)(CN)3] complexes: synthetic challenge, structural characterization and photophysical properties

The substitution of three water molecules around trivalent chromium in CrBr₃·6H₂O with the tridentate 2,2′:6′,2′′-terpyridine (tpy), N,N′-dimethyl-N,N′-di(pyridine-2-yl)pyridine-2,6-diamine (ddpd) or 2,6-di(quinolin-8-yl)pyridine (dqp) ligands gives the heteroleptic mer-[Cr(L)Br₃] complexes. Stepwise treatments with Ag(CF₃SO₃) and KCN under microwave irradiations provide mer-[Cr(L)(CN)₃] in moderate yields. According to their X-ray crystal structures, the associated six-coordinate meridional [CrN₃C₃] chromophores increasingly deviate from a pseudo-octahedral arrangement according to L = ddpd ≈ dpq ≪ tpy; a trend in line with the replacement of six-membered with five-membered chelate rings around Cr^III. Room-temperature ligand-centered UV-excitation at 18 170 cm⁻¹ (λ_exc = 350 nm), followed by energy transfer and intersystem crossing eventually yield microsecond metal-centered Cr(²E → ⁴A₂) phosphorescence in the red to near infrared domain 13 150–12 650 cm⁻¹ (760 ≤ λ_em ≤ 790 nm). Decreasing the temperature to liquid nitrogen (77 K) extends the emission lifetimes to reach the millisecond regime with a record of 4.02 ms for mer-[Cr(dqp)(CN)₃] in frozen acetonitrile.

The heteroleptic mer-[Cr(L)(CN)₃] (L = tpy, ddpd, dqp) complexes with their C_2v-symmetrical [CrC₃N₃] luminescent chromophores represent the missing links between pseudo-octahedral [CrN₆] and [CrC₆] units found in their well-known homoleptic parents.

Magnetic and Luminescence Properties of 8-Coordinate Holmium(III) Complexes Containing 4,4,4-Trifluoro-1-Phenyl- and 1-(Naphthalen-2-yl)-1,3-Butanedionates

A new series of mononuclear Ho³⁺ complexes derived from the β-diketonate anions: 4,4,4-trifluoro-1-phenyl-1,3-butanedioneate (btfa⁻) and 4,4,4-trifuoro-1-(naphthalen-2-yl)-1,3-butanedionate (ntfa⁻) have been synthesized, [Ho(btfa)₃(H₂O)₂] (1a), [Ho(ntfa)₃(MeOH)₂] (1b), (1), [Ho(btfa)₃(phen)] (2), [Ho(btfa)₃(bipy)] (3), [Ho(btfa)₃(di-^tbubipy)] (4), [Ho(ntfa)₃(Me₂bipy)] (5), and [Ho(ntfa)₃(bipy)] (6), where phen is 1,10-phenantroline, bipy is 2,2′-bipyridyl, di-^tbubipy is 4,4′-di-tert-butyl-2,2′-bipyridyl, and Me₂bipy is 4,4′-dimethyl-2,2′-bipyridyl. These compounds have been characterized by elemental microanalysis and infrared spectroscopy as well as single-crystal X-ray difraction for 2–6. The central Ho³⁺ ions in these compounds display coordination number 8. The luminescence-emission properties of the pyridyl adducts 2–6 display a strong characteristic band in the visible region at 661 nm and a series of bands in the NIR region (excitation wavelengths (λ_ex) of 367 nm for 2–4 and 380 nm for 5 and 6). The magnetic properties of the complexes revealed magnetically uncoupled Ho³⁺ compounds with no field-induced, single-molecule magnet (SMMs).

Metal-Based Linear Light Upconversion Implemented in Molecular Complexes: Challenges and Perspectives

The piling up of low-energy photons to produce light beams of higher energies while exploiting the nonlinear optical response of matter was conceived theoretically around 1930 and demonstrated 30 years later with the help of the first coherent ruby lasers. The vanishingly small efficacy of the associated light-upconversion process was rapidly overcome by the implementation of powerful successive absorptions of two photons using linear optics in materials that possess real intermediate excited states working as relays. In these systems, the key point requires a favorable competition between the rate constant of the excited-state absorption (ESA) and the relaxation rate of the intermediate excited state, the lifetime of which should be thus maximized. Chemists and physicists therefore selected long-lived intermediate excited states found (i) in trivalent lanthanide cations doped into ionic solids or into nanoparticles (^2S+1L_J spectroscopic levels) or (ii) in polyaromatic molecules (triplet states) as the logical activators for designing light upconverters using linear optics. Their global efficiency has been stepwise optimized during the past five decades by using indirect intermolecular sensitization mechanisms (energy transfer upconversion = ETU) combined with large absorption cross sections.The induction of light-upconversion operating in a single discrete entity at the molecular level is limited to metal-based units and remained a challenge for a long time because coordination complexes possess high-frequency oscillators incompatible with the existence of (i) scales of accessible excited relays with long lifetimes and (ii) final high-energy emissive levels with noticeable intrinsic quantum yields. In contrast to intermolecular energy transfer processes operating in metal-based doped solids, which require statistical models, the combination of sensitizers and activators within the same molecule limits energy transfers to easily tunable intramolecular processes with first-order kinetic rate constants. Their successful programming in a trinuclear CrErCr complex in 2011 led to the first detectable near-infrared to green light upconversion induced in a molecular unit under reasonable excitation intensity. The subsequent progress in the modeling and understanding of the key factors controlling metal-based light upconversion operating in molecular complexes led to a burst of various designs exploiting different mechanisms, excited-state absorption (ESA), energy transfer upconversion (ETU), cooperative luminescence (CL), and cooperative upconversion (CU), which are discussed in this Account.

Novel Lanthanide (III) Complexes Derived from an Imidazole-Biphenyl-Carboxylate Ligand: Synthesis, Structure and Luminescence Properties

A series of neutral mononuclear lanthanide complexes [Ln(HL)₂(NO₃)₃] (Ln = La, Ce, Nd, Eu, Gd, Dy, Ho) with rigid bidentate ligand, HL (4'-(1H-imidazol-1-yl)biphenyl-4-carboxylic acid) were synthesized under solvothermal conditions. The coordination compounds have been characterized by infrared spectroscopy, thermogravimetry, powder X-ray diffraction and elemental analysis. According to X-ray diffraction, all the complexes are a series of isostructural compounds crystallized in the P2/n monoclinic space group. Additionally, solid-state luminescence measurements of all complexes show that [Eu(HL)₂(NO₃)₃] complex displays the characteristic emission peaks of Eu(III) ion at 593, 597, 615, and 651 nm.

Stepwise Increase of NdIII -Based Phosphorescence by AIE-Active Sensitizer: Broadening the AIPE Family from Transition Metals to Discrete Near-Infrared Lanthanide Complexes*

We designed two near-infrared (NIR) lanthanide complexes [(L)₂ -Nd(NO₃ )₃ ] (L=TPE₂ -BPY for 1, TPE-BPY for 2) by employing aggregation-induced emission (AIE)-active tetraphenylethylene (TPE) derivatives as sensitizers, which possessed matched energy to Nd^III , prevented competitive deactivation under aggregation, even shifted the excitation window toward 600 nm by twisted intramolecular charge transfer. Furthermore, benefiting from the 4 f electron shielding effect and antenna effect, the enhanced excitation energies of the AIE-active sensitizers by structural rigidification transferred into the inert Nd^III excited state through ³ LMCT, affording the first aggregation-induced phosphorescence enhancement (AIPE)-active discrete NIR-emitting lanthanide complexes. As 1 equipped with more AIE-active TPE than 2, L→Nd energy transfer efficiency in the former was higher than that in the latter under the same conditions. Consequently, the crystal of 1 exhibited one of the longest lifetimes (9.69 μs) among Nd^III -based complexes containing C-H bonds.

Accessing Lanthanide-to-Lanthanide Energy Transfer in a Family of Site-Resolved [LnIII LnIII '] Heterodimetallic Complexes

The ligand H₃ L (6-[3-oxo-3-(2-hydroxyphenyl)propionyl]pyridine-2-carboxylic acid), which exhibits two different coordination pockets, has been exploited to engender and study energy transfer (ET) in two dinuclear [Ln^III Ln^III '] analogues of interest, [EuYb] and [NdYb]. Their structural and physical properties have been compared with newly synthesised analogues featuring no possible ET ([EuLu], [NdLu], and [GdYb]) and with the corresponding homometallic [EuEu] and [NdNd] analogues, which have been previously reported. Photophysical data suggest that ET between Eu^III and Yb^III does not occur to a significant extent, whereas emission from Yb^III originates from sensitisation of the ligand. In contrast, energy migration seems to be occurring between the two Nd^III centres in [NdNd], as well as in [NdYb], in which Yb^III luminescence is thus, in part, sensitised by ET from Nd. This study shows the versatility of this molecular platform to further the investigation of lanthanide-to-lanthanide ET phenomena in defined molecular systems.

Influence of a Lanthanide Ion on the Ni Site of a Heterobimetallic 3d-4f Mabiq Complex

This work presents the synthesis and characterization of a 3d-4f bimetallic complex based on the redox-active macrocyclic biquinazoline ligand, Mabiq. The mixed Yb-Ni complex, [(Cp*)₂Yb(Mabiq)Ni]BArF (3), was synthesized upon reaction of [Ni^II(Mabiq)]BArF (2) with (Cp*)₂Yb^II(OEt₂). The molecular structures of 3 and its sister complex, [(Cp*)₂Yb(Mabiq)Ni][(Cp*)₂Yb(OTf)₂] (1), confirmed the presence of a Yb(III) center and a reduced Ni-Mabiq unit. Spectroscopy (absorption and NMR), cyclic voltammetry, and magnetic susceptibility studies were employed to analyze the electronic structure of 3, which is best described by the [(Cp*)₂Yb^III(Mabiq^•)Ni^II]⁺ formulation. Notably, the ligand-centered radical is delocalized over both the diketiminate and bipyrimidine units of the Mabiq ligand. The magnetic susceptibility and variable temperature NMR studies for 3 denote coupling between the Ni-Mabiq site and the peripheral Yb center-previously unobserved in 3d-3d Mabiq complexes. The complex nature of the exchange interactions is highlighted by the multiconfigurational ground state for 3, comprising nearly degenerate singlet and triplet states.

Effect of the aromatic substituent on the para-position of pyridine-bis(oxazoline) sensitizers on the emission efficiency of their EuIII and TbIII complexes

Two efficient lanthanide ion sensitizers 2,6-bis(oxazoline)-4-phenyl-pyridine (PyboxPh, 1) and 2,6-bis(oxazoline)-4-thiophen-2-yl-pyridine (Pybox2Th, 2) were synthesized. 1 crystallizes in the monoclinic space group P21/c with cell parameters a = 16.3794(4) Å, b = 7.2856(2) Å, c = 11.7073(3) Å, β = 97.229(1)° and V = 1385.97(6) Å3. 2 crystallizes in the monoclinic space group P21/n with cell parameters a = 5.9472(2), b = 16.0747(6), c = 14.3716(5) Å, β = 93.503(1)° and V = 1371.35(8) Å3. Photophysical characterization of 1 shows that its triplet state energy is located at 22 250 cm-1 and efficient energy transfer is observed for EuIII and TbIII. Solutions of [Ln(PyboxPh)3]3+ in dichloromethane display an emission efficiency of 37.2% for Ln[double bond, length as m-dash]Eu and 24.0% for Ln[double bond, length as m-dash]Tb. The excited state lifetimes for EuIII and TbIII are 2.227 ms and 723 μs, respectively. The triplet state energy of 2 is located at 19 280 cm-1 and is therefore too low to efficiently sensitize TbIII emission. However, the sensitization of EuIII is effective, with an emission quantum yield of 14.5% and an excited state lifetime of 714 μs. This shows that the derivatization of the chelator is strongly influenced by the aromatic substituents on the para-position of the pyridine ring. New isostructural 1 : 1 complexes of PyboxPh with EuIII (3) and TbIII (4) were also isolated and crystallize in the triclinic space group P1[combining macron] with cell parameters a = 9.1845(2) Å, b = 10.3327(2) Å, c = 11.9654(2) Å, α = 98.419(1)°, β = 108.109(1)°, γ = 91.791(1)°, V = 1064.08(4) Å3 and a = 7.8052(1) Å, b = 11.8910(1) Å, c = 14.2668(2) Å, α = 72.557(1)°, β = 86.355(1)°, γ = 77.223(1)°, V = 1231.95(3) Å3, respectively.

Near-IR to Near-IR Upconversion Luminescence in Molecular Chromium Ytterbium Salts

Upconversion photoluminescence in hetero-oligonuclear metal complex architectures featuring organic ligands is an interesting but still rarely observed phenomenon, despite its great potential from a basic research and application perspective. In this context, a new photonic material consisting of molecular chromium(III) and ytterbium(III) complex ions was developed that exhibits excitation-power density-dependent cooperative sensitization of the chromium-centered 2 E/2 T1 phosphorescence at approximately 775 nm after excitation of the ytterbium band 2 F7/2 →2 F5/2 at approximately 980 nm in the solid state at ambient temperature. The upconversion process is insensitive to atmospheric oxygen and can be observed in the presence of water molecules in the crystal lattice.

Isocyanate Insertion into a La-P Phosphide Bond: A Versatile Route to Phosphaureate-Bridged Heterobimetallic Lanthanide-Coinage-Metal Complexes

A new route to heterobimetallic lanthanide-coinage-metal complexes is disclosed. The selective insertion of organic substrates such as phenyl iso(thio)cyanate into the La-P bond of the primary phosphido complex (PN)2La(PHMes) (1) (with PN- = (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide) yields the phospha(thio)ureate complexes (PN)2La(OC(NPh)(PHMes)) (2) and (PN)2La(SC(NPh)(PHMes)) (3) with retention of the PH protons. Subsequent deprotonation of the phosphaureate complex 2 with potassium hexamethyldisilazide (KHMDS, K[N(SiMe3)2]) leads to the polymeric complex [K{(PN)2La(OC(NPh)(PMes))}]n (4). Complex 4 was found to be an excellent precursor for salt metathesis reactions with copper(I) and gold(I) chlorides supported by an N-heterocyclic carbene (NHC, 5 and 6) or a cyclic alkyl amino carbene (CAAC, 7 and 8). This resulted in the unprecedented formation of heterobimetallic lanthanum-coinage-metal complexes, containing the first example of a μ,κ2(O,N):κ1(P)-phosphaureate bridging ligand. For an alternative route to complex 8 a direct protonolysis protocol between a new basic gold(I) precursor, namely (MeCAAC)Au(HMDS), and 2 was also investigated. The complexes have been characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray crystallography (except for 8).

White light emission from a green cyclometalated platinum(ii) terpyridylphenylacetylide upon titration with Zn(ii) and Eu(iii )

The cyclometalated Pt(ii) acetylide derivative with a 1,3-bis(N-octyl-benzimidazol-2-yl)benzene (N^C^N) ligand and a free terpyridine (TPY) receptor has been successfully synthesized and characterized. X-ray crystallography shows its inefficient conjugation degree between the [(N^C^N)Pt] and TPY planes. This bifunctional complex shows an enhanced 1MLCT/LLCT absorption band (ε = 3.30 × 104 dm3 mol-1 cm-1) centered at λmax = 365 nm, and the well-resolved vibronic-structured 3MLCT/LLCT emission bands (Φ = 0.08, τ = 3.43 μs) in the range of ca. 475-700 nm. Consecutive titrations show that added Zn2+ and Eu(HFA)3 bond to its free TPY receptor with 1 : 2 and 1 : 1 stoichiometry to form the heterotrinuclear Pt-Zn-Pt (Ka = 3.48 × 104 mol-1 dm3) and heterodinuclear Pt-Eu (Ka = 1.73 × 104 mol-1 dm3) complexes, respectively. A sensitizing effect of Zn2+ on the TPY unit, and the incomplete d → f energy transfer from the [(N^C^N)Pt(ii)] antenna donor to the Eu(iii) center with maximum efficiency of 51.8% are observed. Using an in situ mixed titration strategy, the R/G/B emission triads consisted of red [(TPY)Eu(HFA)3] and green [(N^C^N)Pt(ii)] dual phosphorescence and blue [(TPY)Zn(TPY)] fluorescence, which can be well balanced to realize the white-light-emission with CIE coordinates (x = 0.36, y = 0.36) by precisely controlling the molar ratio (9 : 1 : 2) of the parent complexes, Eu(HFA)3 and Zn(ClO4)2.

Luminescent lanthanide metal-organic framework nanoprobes: from fundamentals to bioapplications

Metal-organic frameworks (MOFs), a unique type of porous material characterized by high porosity, large internal surface area and remarkable structural tunability, have emerged as very attractive functional materials for a variety of applications. As a promising subclass of MOFs, lanthanide metal-organic frameworks (Ln-MOFs) integrate the unique advantages of MOFs and the intrinsic features of lanthanide ions, such as sharp emission bands, long luminescent lifetimes, large Stokes shifts, high color purity and high resistance to photobleaching. In this minireview, we provide a brief overview of the most recent advances in luminescent Ln-MOF nanoprobes, which covers from their chemical and physical fundamentals to bioapplications, including their synthetic strategies, optical properties and promising bioapplications in biodetection, bioimaging and therapy. Finally, some of the most important emerging trends and future efforts toward this rapidly evolving field are also envisioned.

Monitoring Fe(II) Spin-State Equilibria via Eu(III) Luminescence in Molecular Complexes: Dream or Reality?

The modulation of light emission by Fe(II) spin-crossover processes in multifunctional materials has recently attracted major interest for the indirect and noninvasive monitoring of magnetic information storage. In order to approach this goal at the molecular level, three segmental ligand strands, L4-L6, were reacted with stoichiometric mixtures of divalent d-block cations (M(II) = Fe(II) or Zn(II)) and trivalent lanthanides (Ln(III) = La(III) or Eu(III)) in acetonitrile to give C₃-symmetrical dinuclear triple-stranded helical [LnM(Lk)₃]⁵⁺ cations, which can be crystallized with noncoordinating counter-anions. The divalent metal M(II) is six-coordinate in the pseudo-octahedral sites produced by the facial wrapping of the three didentate binding units, the ligand field of which induces variable Fe(II) spin-state properties in [LnFe(L4)₃]⁵⁺ (strictly high-spin), [LnFe(L5)₃]⁵⁺ (spin-crossover (SCO) around room temperature), and [LnFe(L6)₃]⁵⁺ (SCO at very low temperature). The introduction of the photophysically active Eu(III) probe in [EuFe(Lk)₃]⁵⁺ results in europium-centered luminescence modulated by variable intramolecular Eu(III) → Fe(II) energy-transfer processes. The kinetic analysis implies Eu(III) → Fe(II) quenching efficiencies close to 100% for the low-spin configuration and greater than 95% for the high-spin state. Consequently, the sensitivity of indirect luminescence detection of Fe(II) spin crossover is limited by the resulting weak Eu(III)-centered emission intensities, but the dependence of the luminescence on the temperature unambiguously demonstrates the potential of indirect lanthanide-based spin-state monitoring at the molecular scale.

Near-infrared/visible-emitting nanosilica modified with silylated Ru(II) and Ln(III) complexes

Three luminescent silica-based nanohybrids were fabricated by grafting of silylated Ru(II) and Nd/Yb(III) complexes onto mesoporous silica nanoparticles obtained by microemulsion method. The prepared nanohybrids were characterized by Fourier transform-Raman spectroscopy, solid state-nuclear magnetic resonance, high resolution-transmission electron microscopy and scanning and transmission electron microscopy techniques. The chemical integrity and the grafting of all complexes inside MSNs nanopores as well as a good distribution of metal complexes onto MSNs surface were achieved for all nanohybrids. Photophysical results revealed that by monitoring the excitation on Ru(II) moieties from SiO ₂ -RuNd and SiO ₂ -RuYb nanohybrids, the sensitization of NIR-emitting Nd/Yb(III) ions were successfully detected via energy transfer processes. Energy transfer rates (k _EnT) of 0.20 × 10⁷ and 0.11 × 10⁷ s^-1 and efficiencies of energy transfer (η _EnT) of 40% and 27.5% were obtained for SiO ₂ -RuNd and SiO ₂ -RuYb nanohybrids, respectively. These results confirm the preparation of promising dual (near-infrared/visible)-emitting silica-based nanohybrids as new nanotools for applications as nanosensores and nanomarkers.

Luminescent Ir(iii)–Ln(iii) coordination polymers showing slow magnetization relaxation

Two structural types of iridium(iii)–lanthanide(iii) coordination polymers, single-chain Ir2Ln and double-chain Ir4Ln2 (Ln = Gd, Dy, Er, and Yb), have been prepared. SMM behaviour and NIR luminescence were observed for the Ir–Er and Ir–Yb systems.

Wheel-like 6 luminescent lanthanide complexes covering the visible and near-infrared domains

Luminescence properties of wheel-like lanthanide complexes.

Heteronuclear d-d and d-f Ru(ii)/M complexes [M = Gd(iii), Yb(iii), Nd(iii), Zn(ii) or Mn(ii)] of ligands combining phenanthroline and aminocarboxylate binding sites: combined relaxivity, cell imaging and photophysical studies

A ligand skeleton combining a 1,10-phenanthroline (phen) binding site and one or two heptadentate N3O4 aminocarboxylate binding sites, connected via alkyne spacers to the phen C3 or C3/C8 positions, has been used to prepare a range of heteronuclear Ru·M and Ru·M2 complexes which have been evaluated for their cell imaging, relaxivity, and photophysical properties. In all cases the phen unit is bound to a {Ru(bipy)2}2+ unit to give a phosphorescent {Ru(bipy)2(phen)}2+ luminophore, and the pendant aminocarboxylate sites are occupied by a secondary metal ion M which is either a lanthanide [Gd(iii), Nd(iii), Yb(iii)] or another d-block ion [Zn(ii), Mn(ii)]. When M = Gd(iii) or Mn(ii) these ions provide the complexes with a high relaxivity for water; in the case of Ru·Gd and Ru·Gd2 the combination of high water relaxivity and 3MLCT phosphorescence from the Ru(ii) unit provides the possibility of two different types of imaging modality in a single molecular probe. In the case of Ru·Mn and Ru·Mn2 the Ru(ii)-based phosphorescence is substantially reduced compared to the control complexes Ru·Zn and Ru·Zn2 due to the quenching effect of the Mn(ii) centres. Ultrafast transient absorption spectroscopy studies on Ru·Mn (and Ru·Zn as a non-quenched control) reveal the occurrence of fast (<1 ns) PET in Ru·Mn, from the Mn(ii) ion to the Ru(ii)-based 3MLCT state, i.e. MnII-(phen˙-)-RuIII → MnIII-(phen˙-)-RuII; the resulting MnIII-(phen˙-) state decays with τ ≈ 5 ns and is non-luminescent. This occurs in conformers when an ET pathway is facilitated by a planar, conjugated bridging ligand conformation connecting the two units across the alkyne bridge but does not occur in conformers where the two units are electronically decoupled by a twisted conformation of the bridging ligand. Computational studies (DFT) on Ru·Mn confirmed both the occurrence of the PET quenching pathway and its dependence on molecular conformation. In the complexes Ru·Ln and Ru·Ln2 (Ln = Nd, Yb), sensitised near-infrared luminescence from Nd(iii) or Yb(iii) is observed following photoinduced energy-transfer from the Ru(ii) core, with Ru → Nd energy-transfer being faster than Ru → Yb energy-transfer due to the higher density of energy-accepting states on Nd(iii).

Luminescent nanohybrids based on silica and silylated Ru(II)-Yb(III) heterobinuclear complex: new tools for biological media analysis

Lanthanide (Ln) complexes emitting in the near-infrared (NIR) region have fostered great interest as upcoming optical tags owing to their high spatial and temporal resolution emission as well deeper light penetration in biological tissues for non-invasive monitoring. For use in live-cell imaging, lanthanide complexes with long-wavelength absorption and good brightness are especially critical. Light-harvesting ligands of Ln complexes are typically excited in the ultraviolet region, which in turn trigger simultaneously autofluorescence and long-exposition damage of living systems. The association of d-metalloligands rather than organic chromophores enables the excitation of NIR-emitting Ln complex occurs in the visible region. Taking advantage of the long-lived excited states and intense absorption band in the ultraviolet (UV) to NIR region of Ru(II), we successfully design a dual-emitting (in the visible and NIR region) d-f heterobinuclear complex based on Ru(II) metalloligand and Yb(III) complex. In addition, we developed luminescent nanohybrids by grafting of Ru(II)-Yb(III) heterobinuclear complexes containing silylated ligands on the surface of mesoporous and dense silica matrix. The nanomarkers were successfully applied for imaging of murine melanoma B16-F10 and neonatal human dermal fibroblast HDFn cell cultures by one-photon or two-photon absorption using laser scanning confocal microscopy. Great cellular uptake, low cytotoxicity and the possibility to achieve visible and NIR emission via two-photons excitation show that the nanohybrids are remarkable markers for in vitro and a potential tool for in vivo applications.

Nanoscale fluorescent metal-organic framework composites as a logic platform for potential diagnosis of asthma

Asthma is a common chronic disorder, and the decreased hydrogen sulfide (H₂S) production in the lung has been considered as an early detection biomarker for asthma. However, the detection of H₂S in biological systems remains a challenge; because it requires the designed sensors to have the following features: nanoscale size, good biocompatibility, real-time detection, high selectivity/sensitivity, and good water stability. Here, we propose the potential of using nanoscale fluorescent metal-organic framework (MOF) composites Eu³⁺/Ag⁺@UiO-66-(COOH)₂ (hereafter denoted as EAUC) as a logic platform for tentative diagnosis of asthma by detecting the biomarker H₂S. This INHIBIT logic gate based on Eu³⁺@UiO-66-(COOH)₂ (EUC) can be produced by choosing Ag⁺ and H₂S as inputs and by monitoring the fluorescent signal (I₆₁₅) as an output. Our fluorescent studies indicate that the EAUC exhibits excellent selectivity, extreme sensitivity (limit of detection: 23.53 μM), and real-time in situ detection of H₂S. Further, MTT analysis in PC12 cells shows that the EAUC possesses low cytotoxicity and favourable biocompatibility that are suitable for the detection of biomarker H₂S in vivo, as demonstrated by the successful detection of spiked H₂S in the diluted serum samples. This work represents the possibility of using MOF-based logic platform for tentative diagnosis of asthma in clinical medicine.

Near-infrared emissive Er(iii) and Yb(iii) molecular nanomagnets in metal–organic chains functionalized by octacyanidometallates(iv)

Photoluminescent single-molecule magnets are formed in lanthanide(pyrazine N,N′-dioxide) chains with octacyanidometallate(iv) coordination branches playing a crucial role in sensitized NIR emission.

Regulating structural dimensionality and emission colors by organic conjugation between SmIII at a fixed distance

The conjugation of bridging bis(diphenylphosphine oxide) alkane or arene ligands was found to control the structural dimensionality and the emission color of complexes from reactions with SmIII(hfac)3(H2O)2 (hfac- = hexafluoroacetylacetonato) while retaining the SmSm distances. Bis(diphenylphosphine oxide)-1,4-butane (L1) affords a one-dimensional (1D) ribbon {Sm(hfac)3(L1)}∞ (1) that emits red color, while bis(diphenyl-phosphinoyl)-1,4-benzene (L2) results in a two-dimensional (2D) network {Sm(hfac)2(CF3COO)(L2)3}∞ (2) and near-white emission, but bis(diphenyl-phosphinoyl)-9,10-anthracene (L3) forms a zero-dimensional (0D) cyclic structure {Sm(hfac)3(L3)}2 (3) with strong ππ interactions that emit green color. Noticeably, the conjugation change is accompanied by a configurational change of coordination from trans for 1 and 2 to cis for 3. The color change is associated with the superposition of ligand and Sm based electronic band energies and their intensities. Such white light emission by a single compound having contributions from different building components is quite rare.

Ratiometric fluorescence sensing of mercuric ion based on dye-doped lanthanide coordination polymer particles

This work focused on the development of a novel ratiometric fluorescence sensor for detection of Hg²⁺ by using dye-doped lanthanide infinite coordination polymer (Ln-ICP) particles. The dye-doped Ln-ICP used herein was prepared by self-assemble of adenosine monophosphate (AMP) with Ce³⁺ and Tb³⁺ (Ce/Tb-AMP) through self-adaptive chemistry, in which the fluorescent dye coumarin was encapsulated during the assembly process as a guest molecule. Under 310 nm irradiation, the obtained coumarin@Ce/Tb-AMP itself emitted characteristic green luminescence of Tb³⁺, accompanied with a weak fluorescence at 445 nm originated from coumarin encapsulated in the Ce/Tb-AMP networks. The fluorescence emission of coumarin became strong when it was released to the solution. In the presence of Hg²⁺, the coumarin@Ce/Tb-AMP was destroyed due to the specific coordination interaction between AMP and Hg²⁺, which leaded to the release of coumarin to the solution meanwhile. Consequently, the fluorescence of Ce/Tb-AMP was quenched, while that of coumarin enhanced. On the basis of this strategy, we developed a novel ratiometric fluorescent sensor for the detection of Hg²⁺ by measuring the ratio of fluorescent intensity of the coumarin@Ce/Tb-AMP suspension, which showed a wide linear range from 0.08 to 1000 nM and detection limit of 0.03 nM with high selectivity and sensitivity. Furthermore, the constructed ratiometric fluorescent sensor was successfully applied in detecting Hg²⁺ in drinking water and human blood serum (HBS) with satisfactory results.

Sensitized near infrared emission through supramolecular d → f energy transfer within an ionic Ru(ii)-Er(iii) pair

The newly synthesized ionic triple salt Ru-Er, {[Ru^II(bpy)₂(dbim)][Er^III(hfac)₄][CF₃COO]·H₂O} (bpy = 2,2'-bipyridine; hfac^- = hexafluoroacetylacetonate; dbim = 2,2'-dibenzimidazole) exhibits near-infrared (NIR) emission at 1535 nm by intermolecular Ru → Er (d → f) energy transfer across supramolecular interactions when pumped within the Ru(ii) ³MLCT band. It is the first such observation for a transition metal-lanthanide ionic pair.

Color tuning and white light emission by codoping in isostructural homochiral lanthanide metal–organic frameworks

Pure white-light emission and fluent light-emitting color change can be facilely obtained by codoping isostructural homochiral lanthanide metal–organic frameworks.

Anion-induced 3d–4f luminescent coordination clusters: structural characteristics and chemical fixation of CO2 under mild conditions

Anion-induced clusters with luminescence exhibit excellent catalysis to transform CO₂ into cyclic carbonates under mild conditions.