Functionalized Lanthanide(III) Complexes Constructed from Azobenzene Derivative and β-Diketone Ligands: Luminescent, Magnetic, and Reversible Trans-to-Cis Photoisomerization Properties

Abstract

The coordination ability of ligands functionalized by azobenzene was manipulated, and two novel chelating ligands, (E)-4-(phenyldiazenyl)-N,N-bis(pyridin-2-ylmethyl) benzohydrazide (CHNO, PBPM) and (E)-4-((4-(dimethylamino)phenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl) benzohydrazide (CHNO, dmPBPM), were synthesized. The ligands can offer four coordinating atoms (one oxygen and three nitrogens) to act as tetradendate ligands, together with the two β-diketonates (4,4,4-trifluoro-1-phenylbutane-1,3-dionate, tfd), and the trifluoroacetate anion presented as a ligand and a counterion to form the quaternary units with lanthanide(III) ions (La, Eu, and Gd), [Ln(tfd)(PBPM)(CFCO)] (LnCHFNO) and [Ln(tfd)(dmPBPM)(CFCO)] (LnCHFNO), where the lanthanide(III) ions are nine coordinated with NO donor sets. All six complexes were structurally characterized, and four crystals were obtained and further analyzed by means of single-crystal X-ray diffraction. They all crystallized in the monoclinic P2/c space group with very similar lattice parameters, forming a monocapped twisted square antiprism. We successfully observed the photoluminescent properties of Eu(III) complexes at a wavelength of 614 nm in both solution and the solid state, as well as the trans-to-cis photoisomerization with the quantum yield (Φ = 10) of [Eu(tfd)(PBPM)(CFCO)] complex that was comparable to that of PBPM. Moreover, the trans-to-cis photoisomerization rates of complexes [Ln(tfd)(PBPM)(CFCO)] (La, Eu, Gd) (10-10 s ) were also at the same level as that of PBPM and much higher than azobenzene itself (10-10 s). With the aid of TD-DFT calculations, the luminescence of Eu(III) complexes was found to originate from the attenuation effect of β-diketonates. These features provide the foundation for the development of azobenzene-derived β-diketonates lanthanide(III) complexes with photoisomerization and photoluminescence dual functions.

Near-Infrared Photoluminescence and Reversible Trans-to-Cis Photoisomerization of Mononuclear and Binuclear Ytterbium(III) Complexes Functionalized by Azobenzene Groups

“…We subsequently manipulated the ligands and designed ( E )-4-(phenyldiazenyl)- N , N -bis(pyridin-2-ylmethyl) benzohydrazide lanthanide complexes. 20 We detected trans-to-cis photoisomerization and visible emission of 614 nm from Eu 3+ in the complexes in solution. This is remarkable, although it is not very useful from a practical biological viewpoint, owing to the strong optical interference generated by the biological samples.…”

Tuneable Emission of Polyhedral Oligomeric Silsesquioxane Based Nanostructures that Self‐Assemble in the Presence of Europium(III) Ions: Reversible trans‐to‐cis Isomerization

“…On/off fluorescent switching [15] and photostabilization [16] via reversible cis-trans isomerization have been also reported. [17] Photo-induced polymerization [18] as well as cis-trans photoisomerization studies [19] in the presence of silsesquioxane nano-cages have been reported as well.…”

“…In some cases, configurational changes can be associated with different fluorescence emissions regulated by the photoisomerization process. On/off fluorescent switching and photostabilization via reversible cis‐trans isomerization have been also reported . Photo‐induced polymerization as well as cis‐trans photoisomerization studies in the presence of silsesquioxane nano‐cages have been reported as well.…”

Synthesis and Characterization of Photoresponsive Macromolecule for Biomedical Application

“…However, the cis-form is unstable and liable to reversely isomerize to trans-form under the action of visible light or slight heat (Henzl et al, 2006 ; Kumar and Suresh, 2009 ; Schmidt et al, 2010 ). Given the fact that cis- and trans-isomers of azobenzenes have a different spatial arrangement of the aromatic moieties, physical and chemical properties of azobenzenes varied a lot, some examples being π-π stack interaction among molecules, dipole moments, and surface wettability (Li et al, 2014 ; Yuan et al, 2014 ; Lin et al, 2016 , 2017 ). Consequently, azobenzenes became particularly popular as photoresponsive chromophores in a number of research fields including biomedical fields (Deka et al, 2015 ; Liu et al, 2015 ; Bian et al, 2016a , b ).…”