Construction And Performance Of Triphenylamine-Based Metal-Organic Cages

The research of supramolecular chemistry is based on the molecular assembly and intermolecular interaction.The concept of unique host-guest interaction breaks the traditional mode of chemichal interaction.In recent years,metal-organic cages（MOCs）,as one of the important subunit,have been gradually developed,because of their well-defined hydrophobic cavities and the easy-modified organic ligand with several functional groups which endows them excellent superamolecular behavior to interact with the specific guest molecules.The enriched host-guest interactions in MOCs make it possible to show promising application in the field such as molecular recognition and light-driven hydrogen production.Due to the sharp and intrinsic fluorescence emission in the visible area,luminescent metal-organic cages based on lanthanide ions show a promising application in the field of molecular recognition.However,the formation of analogous lanthanide supramolecular architectures,in contrast to those constructed using transition metals,is more problematic and there are far fewer examples utilizing lanthanides in coordination-driven self-assembly.The versatile coordination numbers（3-12）and coordination geometries of lanthanides make a controlled self-assembly of a predetermined structure rather challenging.In this thesis,the C₃-symmetric bipyridine-based tridentate ligand,L1 was synthesized via an amide coupling between 2,2’-bipyridine-based arms and bridging C₃-symmetric triphenylamine spacers with good optical performance.A luminescent tetrahedral metal-organic cage Tet-Eu has been synthesized by the coordination of Eu（Ⅲ）ions and tridentate ligand L1 containing triphenylamine that activating the lanthanide emission through the so-called“antenna effect”.Without introduction of additional recognition units,high sensitivity and selectivity are revealed for Tet-Eu in dual-responsive turn-off luminescent sensing toward F^-and Picric Acid explosive.The C₃-symmetric bis-tridentate 2,2’-bipyridine-based ligands,L2 with triphenylamine as the bridging unit was designed.Coordinating with bidentate ligand L2,two redox-active tetrahedral metal-organic cages,Tet-Co and Tet-Ni with either Co（II）ions or Ni（II）ions as construction nodes respectively,were synthesized to mimic natural enzymes for their abilities to effectively reduce proton to product hydrogen.Both metal-organic cages,Tet-Co and Tet-Ni could be capable of encapsulating an organic dye molecule（fluorescein,Fl）into their cavities via hydrogen bonding and static attraction to form 1:1 complexation species.The supramolecular system enforces the proximity between the redox catalytic sites and the photosensitizer encapsulated in the pocket and accelerates the photoinduced electron transfer from the excited state of the photosensitizer to the catalytic sites and allows a direct photoinduced electron transfer（PET）process from the excited state*Fl to the redox catalyst.Hence,the formation of supramolecular system prolongs the lifetime of the photosensitizer and increases the efficiency in light-driven hydrogen production.