Strong Fluorescent Lanthanide Salen Complexes: Photophysical Properties, Excited-State Dynamics, and Bioimaging

Abstract

The synthesis, excited-state dynamics, and biological application of luminescent lanthanide salen complexes (Ln = Lu, Gd, Eu, Yb, salen = N,N′-bis(salicylidene)ethylenediamine-based ligands) with sandwich structures are described. Among them, Lu(III) complexes show unusually strong ligand-centered fluorescence with quantum yields up to 62%, although the metal center is close to a chromophore ligand. The excited-state dynamic studies including ultrafast spectroscopy for Ln-salen complexes revealed that their excited states are solely dependent on the salen ligands and the ISC rates are slow (10 8 −10 9 s −1 ). Importantly, time-dependent density functional theory calculations attribute the low energy transfer efficiency to the weak spin−orbital coupling (SOC) between the singlet and triplet excited states. More importantly, Lu-salen has been applied as a molecular platform to construct fluorescence probes with organelle specificity in living cell imaging, which demonstrates the advantages of the sandwich structures as being capable of preventing intramolecular metal−ligand interactions and behaviors different from those of the previously reported Zn-salens. Most importantly, the preliminary study for in vivo imaging using a mouse model demonstrated the potential application of Ln coordination complexes in therapeutic and diagnostic bioimaging beyond living cells or in vitro.

Influence of structural variation of salamo‐based ligand on supramolecular architectures, Hirshfeld analyses, and fluorescence properties of new tetranuclear NiII complexes

“…[ 12 ] Salen‐based ligands tend to coordinate with metal ions to form stable metal salen‐based complexes. [ 13 ] Because of the application of metal salen‐based complexes in optics, [ 14 ] electrochemistry, [ 15 ] magnetism, [ 16 ] and so forth, research on the synthesis, [ 17 ] characterization, [ 18 ] structure determination, [ 19 ] luminescence, [ 20 ] and magnetic materials [ 21 ] of metal salen‐based complexes have become a hot spot. [ 22,23 ]…”

Construction of an Octanuclear Zn(II)‐Yb(III) Schiff Base Complex for the NIR Luminescent Sensing of Nitrofuran Antibiotics

“…Recently, fluorescent sensors for the response of various analytes have attracted extensive attention because of their fast response, convenient utilization and high sensitivities. [ 1‐8 ] Pharmaceutical antibiotics such as nitrofuran antibiotics (NFAs) have been widely employed in many fields such as aquaculture, medical, food processing, etc . However, the abuse of antibiotics also leads to serious environmental pollution, [ 9‐10 ] and the development of reliable detection of antibiotics has attracted growing attention in recent years.…”

Crystal structure and Hirshfeld surface analysis of ((S,S)-2,2′-{[(1,2-diphenylethane-1,2-diyl)bis[(azaniumylylidene)methanylylidene]}bis(6-methoxyphenolato))trinitratosamarium(III)

“…Lanthanide metal complexes can have attractive functions such as magnetism and fluorescence when synthesized with properly designed ligands (Yao et al, 2019;Lin et al, 2009). In recent years, lanthanide complexes that act as single-molecule magnets (SMM) have received much attention (Then et al, 2015).…”