Exploring Differences in Lanthanide Excited State Reactivity Using a Simple Example: The Photophysics of La and Ce Thenoyltrifluoroacetone Complexes

A series of four lanthanide thenoyltrifluoroacetone (TTA) complexes consisting of two f0 (La3+ and Ce4+) and two f1 (Ce3+) complexes was examined using steady-state and time-resolved spectroscopic techniques. The wide range of spectroscopic techniques presented herein have enabled us to discern the nature of the excited states (charge transfer, CT vs ligand localized, LL) as well as construct a Jablonski diagram for detailing the excited state reactivity within the series of molecules. The wavelength and excitation power dependence for these series of complexes are the first direct verification for the presence of simultaneous competing, noninteracting CT and LL excited states. Additionally, a computational framework is described that can be used to support spectroscopic assignments as a guide for future studies. Finally, the relationship between the obtained photophysics and possible photochemical separation mechanisms is described.

A theoretical chemistry-based strategy for the rational design of new luminescent lanthanide complexes: an approach from a multireference SOC-NEVPT2 method

Theoretical methods of the SOC-NEVPT2 type combined with a molecular fragmentation scheme have been proven to be a powerful tool that allows explaining the luminescence sensitization mechanism in Ln(III) coordination compounds through the antenna effect. In this work, we have used this strategy to predict luminescence in a family of compounds of the Eu(R-phen)(BTA)3 type where R-phen = 5-methyl-1,10-phenanthroline (Me-phen), 5-nitro-1,10-71 phenanthroline (Nitro-phen), 4,5-diazafluoren-9-one (One-phen), or 5,6-epoxy-5,6-dihydro-1,10-72 phenanthroline (Epoxy-phen); and BTA = fluorinated β-diketone. Possible sensitization pathways were elucidated from the energy difference between the ligand-centered triplet (³T) states and the emissive excited states of the Eu(III) fragments (Latva rules). Calculations show that the most probable mechanism occurs through the triplet state of the BTA which should be enriched by several parallel energy transfer pathways from R-phen substituents. The complexes were synthesized and structurally characterized by X-ray crystallography and various other physicochemical and spectroscopic methods to realize their optical properties and energy transfer pathways from dual antennae. Experimental results were in good agreement with the theoretical predictions, which reinforces the predictive power of the used theoretical methodology.

Self-assembly and luminescence of trinuclear lanthanide based supramolecular circular helicates

A series of trinuclear lanthanide circular helicates [Ln₃L₃]Cl₃ have been synthesized via supramolecular subcomponent self-assembly. Photophysical studies demonstrate that the unique helical bis-tetradentate 1,29-dialdehyde ligand L^2- could serve as an effective sensitizer for Sm^III, Eu^III, Nd^III and Yb^III ions exhibiting efficient characteristic fluorescence emission because of the shell-type blocking of the ligand, which makes them the first circular helicates exhibiting near-infrared lanthanide fluorescence.

Metal-Coordinated Supramolecular Self-Assemblies for Cancer Theranostics

Metal-coordinated supramolecular nanoassemblies have recently attracted extensive attention as materials for cancer theranostics. Owing to their unique physicochemical properties, metal-coordinated supramolecular self-assemblies can bridge the boundary between traditional inorganic and organic materials. By tailoring the structural components of the metal ions and binding ligands, numerous multifunctional theranostic nanomedicines can be constructed. Metal-coordinated supramolecular nanoassemblies can modulate the tumor microenvironment (TME), thus facilitating the development of TME-responsive nanomedicines. More importantly, TME-responsive organic-inorganic hybrid nanomaterials can be constructed in vivo by exploiting the metal-coordinated self-assembly of a variety of functional ligands, which is a promising strategy for enhancing the tumor accumulation of theranostic molecules. In this review, recent advancements in the design and fabrication of metal-coordinated supramolecular nanomedicines for cancer theranostics are highlighted. These supramolecular compounds are classified according to the order in which the coordinated metal ions appear in the periodic table. Furthermore, the prospects and challenges of metal-coordinated supramolecular self-assemblies for both technical advances and clinical translation are discussed. In particular, the superiority of TME-responsive nanomedicines for in vivo coordinated self-assembly is elaborated, with an emphasis on strategies that enhance the accumulation of functional components in tumors for an ideal theranostic outcome.

Photocytotoxicity of Thiophene- and Bithiophene-Dipicolinato Luminescent Lanthanide Complexes

New thiophene-dipicolinato-based compounds, K₂nTdpa (n = 1, 2), were isolated. Their anions are sensitizers of lanthanide ion (Ln^III) luminescence and singlet oxygen generation (¹O₂). Emission in the visible and near-infrared regions was observed for the Ln^III complexes with efficiencies (ϕ^Ln) ϕ^Eu = 33% and ϕ^Yb = 0.31% for 1Tdpa^2- and ϕ^Yb = 0.07% for 2Tdpa^2-. The latter does not sensitize Eu^III emission. Fluorescence imaging of HeLa live cells incubated with K₃[Eu(1Tdpa)₃] indicates that the complex permeates the cell membrane and localizes in the mitochondria. All complexes generate ¹O₂ in solution with efficiencies (ϕO12) as high as 13 and 23% for the Gd^III complexes of 1Tdpa^2- and 2Tdpa^2-, respectively. [Ln(nTdpa)₃]^3- (n = 1, 2) are phototoxic to HeLa cells when irradiated with UV light with IC₅₀ values as low as 4.2 μM for [Gd(2Tdpa)₃]^3- and 91.8 μM for [Eu(1Tdpa)₃]^3-. Flow cytometric analyses indicate both apoptotic and necrotic cell death pathways.

New Approach in the Application of Conjugated Polymers: The Light-Activated Source of Versatile Singlet Oxygen Molecule

For many years, the research on conjugated polymers (CPs) has been mainly focused on their application in organic electronics. Recent works, however, show that due to the unique optical and photophysical properties of CPs, such as high absorption in UV–Vis or even near-infrared (NIR) region and efficient intra-/intermolecular energy transfer, which can be relatively easily optimized, CPs can be considered as an effective light-activated source of versatile and highly reactive singlet oxygen for medical or catalytic use. The aim of this short review is to present the novel possibilities that lie dormant in those exceptional polymers with the extended system of π-conjugated bonds.

Luminescent lanthanide complexes with a pyridine-bis(carboxamide)-bithiophene sensitizer showing wavelength-dependent singlet oxygen generation

A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized.