Synthesis of Ln(III) chloride tetraphenylporphyrin complexes

Lanthanide porphyrinoids as molecular theranostics

In recent years, lanthanide (Ln) porphyrinoids have received increasing attention as theranostics. Broadly speaking, the term 'theranostics' refers to agents designed to allow both disease diagnosis and therapeutic intervention. This Review summarises the history and the 'state-of-the-art' development of Ln porphyrinoids as theranostic agents. The emphasis is on the progress made within the past decade. Applications of Ln porphyrinoids in near-infrared (NIR, 650-1700 nm) fluorescence imaging (FL), magnetic resonance imaging (MRI), radiotherapy, and chemotherapy will be discussed. The use of Ln porphyrinoids as photo-activated agents ('phototheranostics') will also be highlighted in the context of three promising strategies for regulation of porphyrinic triplet energy dissipation pathways, namely: regioisomeric effects, metal regulation, and the use of expanded porphyrinoids. The goal of this Review is to showcase some of the ongoing efforts being made to optimise Ln porphyrinoids as theranostics and as phototheranostics, in order to provide a platform for understanding likely future developments in the area, including those associated with structure-based innovations, functional improvements, and emerging biological activation strategies.

Lanthanide-tetrapyrrole complexes: synthesis, redox chemistry, photophysical properties, and photonic applications

Tetrapyrrole derivatives such as porphyrins, phthalocyanines, naphthalocyanines, and porpholactones, are highly stable macrocyclic compounds that play important roles in many phenomena linked to the development of life. Their complexes with lanthanides are known for more than 60 years and present breath-taking properties such as a range of easily accessible redox states leading to photo- and electro-chromism, paramagnetism, large non-linear optical parameters, and remarkable light emission in the visible and near-infrared (NIR) ranges. They are at the centre of many applications with an increasing focus on their ability to generate singlet oxygen for photodynamic therapy coupled with bioimaging and biosensing properties. This review first describes the synthetic paths leading to lanthanide-tetrapyrrole complexes together with their structures. The initial synthetic protocols were plagued by low yields and long reaction times; they have now been replaced with much more efficient and faster routes, thanks to the stunning advances in synthetic organic chemistry, so that quite complex multinuclear edifices are presently routinely obtained. Aspects such as redox properties, sensitization of NIR-emitting lanthanide ions, and non-linear optical properties are then presented. The spectacular improvements in the quantum yield and brightness of Yb^III-containing tetrapyrrole complexes achieved in the past five years are representative of the vitality of the field and open welcome opportunities for the bio-applications described in the last section. Perspectives for the field are vast and exciting as new derivatizations of the macrocycles may lead to sensitization of other Ln^III NIR-emitting ions with luminescence in the NIR-II and NIR-III biological windows, while conjugation with peptides and aptamers opens the way for lanthanide-tetrapyrrole theranostics.

Near-Infrared Fluorescent Materials for Sensing of Biological Targets

Near-infrared fluorescent (NIRF) materials are promising labeling reagents for sensitive determination and imaging of biological targets. In the near-infrared region biological samples have low background fluorescence signals, providing high signal to noise ratio. Meanwhile, near-infrared radiation can penetrate into sample matrices deeply due to low light scattering. Thus, in vivo and in vitro imaging of biological samples can be achieved by employing the NIRF probes. To take full advantage of NIRF materials in the biological and biomedical field, one of the key issues is to develop intense and biocompatible NIRF probes. In this review, a number of NIRF materials are discussed including traditional NIRF dye molecules, newly developed NIRF quantum dots and single-walled carbon nanotubes, as well as rare earth metal compounds. The use of some NIRF materials in various nanostructures is illustrated. The enhancement of NIRF using metal nanostructures is covered as well. The fluorescence mechanism and bioapplications of each type of the NIRF materials are discussed in details.

DFT/TDDFT study of lanthanide(III) mono- and bisporphyrin complexes

The electronic structure, molecular structure, and electronic spectra of lanthanide(III) mono- and bisporphyrin complexes are investigated using a DFT/TDDFT method. These complexes include YbP(acac), YbP(2), [YbP(2)](+), YbHP(2), and [YbP(2)](-) (where P = porphine and acac = acetylacetonate). To shed some light on the origin of the out-of-plane displacement of Yb in YbP(acac), unligated model systems, namely, planar D(4h) and distorted C(4nu) YbP, were calculated. For comparison, the calculations were also extended to include the C and [Ce(IV)P(2) ](+) systems. Even without an axial ligand, the lanthanide atom lies considerably above the porphyrin plane; the distortion of the YbP molecular structure from a planar D(4h) to the nonplanar C(4nu) symmetry leads to a considerable energy lowering. The axial ligand makes the metal out-of-plane displacement even larger, and it also changes the redox properties of the lanthanide monoporphyrin. The ground-state configurations of YbP(2) and YbHP(2) were determined by considering several possible low-lying states. YbP(2) is confirmed to be a single-hole radical. The special redox properties of the bisporphyrin complexes can well be accounted for by the calculated ionization potentials and electron affinities. The TDDFT results provide a clear description of the UV-vis and near-IR absorption spectra of the various lanthanide porphyrins.

Mononuclear, Five-Coordinate Lanthanide Amido and Aryloxide Complexes Bearing Tetradentate (N2O2) Schiff Bases

Two monomeric, five-coordinate lanthanide complexes, [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]samarium[2,6-bis(tert-butyl)-4-methylphenoxide] and [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]erbium[2,6-bis(tert-butyl)-4-methylphenoxide], were isolated from the reactions of 2,6-bis(tert-butyl)-4-methylphenol with [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]lanthanide[bis(trimethylsilyl)amido] (lanthanide = Er(3+) and Sm(3+)). The purified phenoxides were recovered in excellent yields and analytical purity, and the reactions proceeded cleanly without Schiff-base degradation or cluster formation. Analogously, [bis-3,3'-(1,3-propanediyldiimino)-1-phenyl-2-butene-1-onato]erbium[bis(trimethylsilyl)amido] was also directly converted to [bis-3,3'-(1,3-propanediyldiimino)-1-phenyl-2-butene-1-onato]erbium[2,6-bis(tert-butyl)-4-methylphenoxide]; however, a less sterically demanding alcohol (i.e., ethanol) yielded a neutral trinuclear oxo alkoxide species with each dianionic Schiff base asymmetrically bridging through micro-oxo interactions. In this polynuclear cluster, each symmetry-related, seven-coordinate erbium(III) ion exhibits monocapped trigonal prismatic geometry, which assembles by sharing triangular capped faces. Single-crystal X-ray diffraction revealed square-pyramidal metal coordination in each five-coordinate lanthanide ion with varied S(4) ruffling of the "square base" donor atoms and the six-membered propylene diamine chelate ring adopting the boat conformation. To contrast the effect of subtle ligand changes, we also report the synthesis and characterization of [bis-5,5'-(2,2-dimethyl-1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]samarium[bis(trimethylsilyl)amido], having gem-dimethyl substituents appended to the propylene bridge central carbon. The six-membered diamine chelate ring in this compound adopts the chair conformation without metal-hydrocarbon interaction. Also presented are qualitative activity observations and polymerization data for the polymerization of rac-lactide and epsilon-caprolactone using the five-coordinate lanthanide amidos and phenoxides.

Facile preparation and photophysics of near-infrared luminescent lanthanide(III) monoporphyrinate complexes

The synthesis, characterization, and single crystal X-ray diffraction structures of a series of monoporphyrinate, trivalent lanthanide complexes with the monoanionic ligands hydridotris(1-pyrazolyl)borate (Tp) and (cyclopentadienyl)tris(diethylphosphinito)cobaltate (L(OEt)) having the general formulas M(TPP)(L) (M = Yb, Tm, Er, Ho, Nd, Pr; TPP = 5,10,15,20-tetraphenylporphyrinate; L = Tp, L(OEt)) are described. The photophysical properties of these complexes are also presented including their absorption, emission, and transient absorption properties.