Synthesis And Photo-Optical Properties Of Poly(N-Heterocyclic Carbene)-Based Organometallic Cages

Various NHC-metal complexes have been developed intensively since the first example was elucidated in 1968.NHC-metal complexes have found huge applications in catalysis,biological medicine and materials science,but there is still much room for research on organometallic light-emitting materials?OLEMs?.The introduction of fluorophores with aggregation-induced emission?AIE?properties during synthesis is an effective method for the preparation of luminescent supramolecular materials.Tetraphenylethylene?TPE?is a typical AIE fluorescent molecule.Although it has been widely studied in metal organic framework materials?MOFs?and supramolecular coordination compounds,only one TPE-based dinuclear NHC-metal complex has been reported.This dissertation mainly focused on the design of TPE-based NHC ligands and the controllable construction of two kinds of organometallic cages.Additionally,turn-on fluorescence in these new organometallic cages has been demonstrated.Thus,we believe that these metal-carbene-based assemblies could be applied in light-emitting materials,fluorescent probes and sensors.The first chapter deals with a detailed introduction about the preparation and application of N-heterocyclic carbene and their metal complexes.Then the development of the aggregation-induced emission?AIE?effect is introduced.The application of tetraphenylethylene?TPE?as a typical aggregation-induced luminescent molecule in detection,imaging,optoelectronic materials as well as the development of supramolecular assemblies involving TPE as the fluorophore are summarized.In the second chapter,we describe a straightforward strategy to construct a series of unprecedented Ag₈L₄?L=ligand?type organometallic cages?OMCs?by employing new tetradentate ligands featuring four triazol-2-ylidene moieties with a TPE core scaffold.While we varied the length of the ligand substituents from ⁿbutyl to ethyl surprisingly smaller Ag₄L₂ organometallic cages were obtained.The structure of the organometallic cage was confirmed by NMR spectroscopy,mass spectrometry and X-ray crystallography.In addition,we studied the photophysical properties of these cage compounds,from the ligand to the organometallic cage,significant fluorescence enhancement and a significantly increased quantum yield??_F from<1%to 64%?was observed.These organometallic cages emit fluorescence in both dilute solutions and solid state.The last chapter deals with the unprecedented structural modulation of the newly synthesized Ag₈L₄ cages under UV irradiation condition.We show that the octanuclear hexadecacarbene complexes Ag₈L₄ can readily switch to exclusively tetranuclear octacarbene complexes Ag₄L₂ under UV irradiation.Thus,a light-triggered quantitative supramolecule-to-supramolecule structural switch through oxidative photocyclization has been achieved.Ag₄L₂ organometallic cage undergoes oxidative photocyclization under UV irradiation.The photo-optical properties of these processes were changed dramatically.