Synthesis And Properties Of Luminescent Metal-organic Cages

Metal-organic cages or cycles（MOCs）,also referred to metal-organic polygons or polyhedra（MOPs）,are discrete structural material created by ligand-assembly of metal ions or metal clusters with organic ligands.As an emerging metal-organic material,MOCs have well-defined size and shape,great symmetry and stability,as well as controllable internal cavities,and can be employed in gas absorption and separation,catalysis,chemical sensing and other fields.In particular,luminescent metal organic cages（LMOCs）materials are a notable branch of MOCs materials,which have active roles in the field of chemical sensing due to their distinctive fluorescence emission capabilities and functionalizable backbone structure.Tetraphenylethylene（TPE）,as a new type of luminescent chromophore with significant aggregation-induced emission（AIE）,can replace the conventional chromophores with traditional aggregation-quenching,and coordinate with metal ions to construct LMOCs with strong luminescence properties.In this work,we designed and synthesized two tetraphenylene（TPE）-based organic ligands with AIE effect,and synthesized MOC materials with novel properties through the solvothermal reaction of organic ligands and metal ions,and investigated their structures and properties separately.There are four main parts:1)An example of an Organic ligand of H₈TDBTPE,containing a phenol hydroxyl group with AIE effect was prepared by combining 1,1,2,2-tetrakis（4-aminophenyl）ethene with 2,3-dimethoxybenzoylchloride.A luminescent metal-organic cage[Ga₈（TDBTPE）₆]（1）was synthesized by solvothermal method.IR spectra,UV spectra,thermogravimetric analysis（TGA）,NMR and TOFMS were applied to describe the structure of complexes 1.The results showed that complex 1 has a higher fluorescence quantum yield of 16.9%,and the fluorescence quantum yield reached 18.6%after removing of solvent molecules.The selective fluorescence sensing of activated 1for hypertensive drugs in methanol were studied.The results revealed that different drugs enable enhance or quench the fluorescence of complex 1 to different degrees.Among them,metoprolol tartrate enhanced the fluorescence of activated 1 by approximately 3-fold,and the limits of detection was 35.113 ppm.The activated complex 1 was fluorescence quenched-by losartan,amlodipine besylate tablets and filodipine,and the detection limits were 0.834 ppm,1.424 ppm and 0.632 ppm,respectively.Therefore,complex 1 has potential value in selective fluorescence sensing of hypertensive drugs.2)Using ETTBA as an organic ligand and synthesized chiral cadmium bisaphthol phosphate（R/S-BPA-Cd）with rigid structure and 2-aminomethylpyridine,two different chirality LMOCs:[Cd₈（ETTBA-PMH）₆（R-BPA）₁₆]（2）and[Cd₈（ETTBA-PMH）₆（S-BPA）₁₆]（3）were synthesized.The fluorescence quantum yields of complex 2 and 3were 20.6%and 21.3%respectively,and the fluorescence quantum yields of activated2 and 3 were 21.8%and 22.7%respectively.In addition,the circular dichroism spectra and circularly polarization luminescence spectra of complexes 2 and 3 were revealed strong mirror symmetry.The selective fluorescence sensing of activated 2 or 3 for chiral amino acid molecules in DMF solvent showed that the quenching efficiency of complex2 by L-Boc-4-nitrophenylalanine was higher than that by D-Boc-4-nitrophenylalanine,and the quenching efficiency of complex 2 by L-Boc-4-nitrophenylalanine was higher than that by D-configuration.Complex 3,meanwhile,showed the opposite.3)A new luminescent metal-organic framework[Cd₃（BTC）₃Cl]（TMPy PE）（H₂O）（4）was designed and synthesized from TMPy PE and encapsulated by a solvothermal reaction.The formation of complex 4 was confirmed by the crystal structure resolved by single crystal X-ray diffraction.The fluorescence quantum yield of 12.8%for activated 4 was higher than that of 11.3%for complex 4.The selective fluorescence detecting studies of activated 4 pairs of antibiotics in aqueous solution were carried out.The results showed that activated 4 showed significant recognition effect on furantoin and furacilin,which could be directly observed by the naked eye,with the lowest detection limits of 0.113 ppm and 0.104 ppm,respectively.Therefore,complex 4 is is an antibiotics sensor with fast response,high selectivity and low detection limit.