Stephen Faulkner

Lanthanide Complexes for Luminescence Imaging Applications

Abstract In this article, imaging applications of luminescent complexes and recent advances in the design and photophysical behaviour of near‐IR responsive complexes are reviewed. Various properties of the luminescent lanthanide complexes are also discussed in detail.

Pure Shift 1H NMR: A Resolution of the Resolution Problem?

Suppressing multiplet structure in 1H??NMR spectra offers a large improvement in spectral resolution (see picture), equivalent to the use of a spectrometer in the GHz range. Such ldquopure shiftrdquo techniques are readily extended to multidimensional methods, for example DOSY.

Luminescence imaging microscopy and lifetime mapping using kinetically stable lanthanide(III) complexes.

The sensitised luminescence from stable lanthanide complexes (1 and 2) bearing a phenanthridine antenna has been used to generate time-resolved images of silica particles. The millisecond order luminescent lifetime of these complexes is utilised to demonstrate time-gated imaging of the sample from a fluorescent background and to facilitate lifetime mapping over the area of the sample.

Sensitised luminescence in lanthanide containing arrays and d–f hybrids

Sensitised luminescence from lanthanide complexes offers many potential advantages in imaging and assay, particularly when coupled with time-gating protocols that can be used to gate out background signal. In this perspective, we discuss the routes by which lanthanide arrays and polymetallic d-f hybrids can be prepared by conventional synthesis and self-assembly, and discuss and evaluate the possibilities for exploiting and evaluating the intermediates in the sensitisation process, with particular emphasis on the mechanisms of energy transfer.

Synthesis and spectroscopic properties of a prototype single molecule dual imaging agent comprising a heterobimetallic rhenium-gadolinium complex.

A luminescent d−f hybrid containing a [Re(bpy)(Ar)(CO)3]+ chromophore and a gadolinium ion bound in a DO3A-derived binding pocket has been prepared. This complex combines long-lived luminescence from the 3MLCT state of the transition metal chromophore with high relaxivity, making it suitable for MRI imaging and luminescence imaging. The analogous complex containing ytterbium exhibits sensitized emission from both the ytterbium center and long-lived emission from the 3MLCT state.

Luminescence from neodymium(III) in solution

Abstract The luminescence lifetime of neodymium(III) in aqueous and organic solutions has been measured for the first time, and the effects of solvent deuteration on the excited state decay kinetics investigated. We have shown that the emissive 4 F 3 2 state is very short lived in water, τ = 29 ± 3 ns, and the lifetimeincreases significantly upon changing to D2O, τ = 152 ± 7 ns. Complexing to polydentate ligands such as EDTA increases the lifetime due to the reduced solvation of the ion by water. In organic solvents the lifetime of the excited state of the ion is affected by both the presence of CH and OH oscillators; the latter are much more efficient at deactivating the excited state.

Reversible Luminescence Switching of a Redox-Active Ferrocene–Europium Dyad

The copper-catalyzed cycloaddition reaction between a propargyl-appended europium complex and azidomethylferrocene yields a d-f dyad whose photophysical properties can be reversibly switched by varying the oxidation state of the ferrocene chromophore.

On the mechanism of d-f energy transfer in RuII/LnIII and OsII/LnIII dyads: Dexter-type energy transfer over a distance of 20 A.

We have used time-resolved luminescence methods to study rates of photoinduced energy transfer (PEnT) from [M(bipy)3]2+ (M=Ru, Os) chromophores to Ln(III) ions with low-energy f-f states (Ln=Yb, Nd, Er) in d-f dyads in which the metal fragments are separated by a saturated -CH2CH2- spacer, a p-C6H4 spacer, or a p-(C6H4)2 spacer. The finding that d-->f PEnT is much faster across a conjugated p-C6H4 spacer than it is across a shorter CH2CH2 spacer points unequivocally to a Dexter-type energy transfer, involving electronic coupling mediated by the bridging ligand orbitals (superexchange) as the dominant mechanism. Comparison of the distance dependence of the Ru-->Nd energy-transfer rate across different conjugated spacers [p-C6H4 or p-(C6H4)2 groups] is also consistent with this mechanism. Observation of Ru-->Nd PEnT (as demonstrated by partial quenching of the RuII-based 3MLCT emission (MLCT=metal-to-ligand charge transfer), and the growth of sensitised NdIII-based emission at 1050 nm) over approximately 20 A by an exchange mechanism is a departure from the normal situation with lanthanides, in which long-range energy transfer often involves through-space Coulombic mechanisms.

Mixed d−f3 Coordination Complexes Possessing Improved Near-Infrared (NIR) Lanthanide Luminescent Properties in Aqueous Solution

The cyclen-based ligand 1, possessing a [1,10]-phenanthroline moiety as a pendant arm, has been used as a ditopic ligand for the complexation of d- and near infrared (NIR) emitting (and) f-metal ions. This ligand forms kinetically stable complexes, 1·Ln, with lanthanide ions such as Ln = ytterbium, neodymium, and lutetium (formed as a non-IR emitting reference compound), the synthesis and photophysical properties of which are described herein in detail. These 1·Ln complexes were then used as building blocks for the formation of mixed d−f heteropolymetallic self-assemblies, where the phen moiety was used to complex a ruthenium (Ru(II)) ion, giving the d−f3 complexes Ru·Ln3 (Ln = Nd(III), Yb(III), Lu(III)). The formation of these supramolecular coordination conjugates was studied by using absorption and luminescence spectroscopy, while the solution structure of the Ru·Lu3 was elucidated by 1H NMR in D2O and H2O. Of these conjugates, both Ru·Nd3 and Ru·Yb3 displayed an intense NIR-emission in H2O at pH 7.4 (with Q(Yb)(L) = 0.073% and Q(Nd)(L) = 0.040%) and in D2O (with QYbL = 0.23% and Q(Nd)(L) = 0.10%). By comparison with their monometallic analogues Ln·1 (Ln = Nd(III), Yb(III)), we demonstrate that our new design possesses an enhanced sensitization efficiency for lanthanide metal centered sensitization upon using the [Ru(phen)3] moiety (d → f energy transfer) as a visibly exciting antenna, and we demonstrate that the intensity of the Ru(II)-based luminescence strictly correlates to the efficiency of the d → f energy transfer processes.

A family of 13 tetranuclear zinc(II)-lanthanide(III) complexes of a [3 + 3] Schiff-base macrocycle derived from 1,4-diformyl-2,3-dihydroxybenzene

A family of thirteen tetranuclear heterometallic zinc(II)-lanthanide(III) complexes of the hexa-imine macrocycle (L(Pr))(6-), with general formula Zn(II)(3)Ln(III)(L(Pr))(NO(3))(3)·xsolvents (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm or Yb), were prepared in a one-pot synthesis using a 3:1:3:3 reaction of zinc(II) acetate, the appropriate lanthanide(III) nitrate, the dialdehyde 1,4-diformyl-2,3-dihydroxybenzene (H(2)L(1)) and 1,3-diaminopropane. A hexanuclear homometallic zinc(II) macrocyclic complex [Zn(6)(L(Pr))(OAc)(5)(OH)(H(2)O)]·3H(2)O was obtained using a 2:0:1:1 ratio of the same reagents. A control experiment using a 1:0:1:1 ratio failed to generate the lanthanide-free [Zn(3)(L(Pr))] macrocyclic complex. The reaction of H(2)L(1) and zinc(II) acetate in a 1:1 ratio yielded the pentanuclear homometallic complex of the dialdehyde H(2)L(1), [Zn(5)(L(1))(5)(H(2)O)(6)]·3H(2)O. An X-ray crystal structure determination revealed [Zn(3)(II)Pr(III)(L(Pr))(NO(3))(2)(DMF)(3)](NO(3))·0.9DMF has the large ten-coordinate lanthanide(III) ion bound in the central O(6) site with two bidentate nitrate anions completing the O(10) coordination sphere. The three square pyramidal zinc(II) ions are in the outer N(2)O(2) sites with a fifth donor from DMF. Measurement of the magnetic properties of [Zn(II)(3)Dy(III)(L(Pr))(NO(3))(3)(MeOH)(3)]·4H(2)O with a weak external dc field showed that it has a frequency-dependent out-of-phase component of ac susceptibility, indicative of slow relaxation of the magnetization (SMM behaviour). Likewise, the Er and Yb analogues are field-induced SMMs; the latter is only the second example of a Yb-based SMM. The neodymium, ytterbium and erbium complexes are luminescent in the solid phase, but only the ytterbium and neodymium complexes show strong lanthanide-centred luminescence in DMF solution.