Synthesis,Structures,Optical Properties Of Coordination Polymers Based On Nitrogen Carboxylic Acid

Coordination Polymers（CPs）which own periodic network structures,are formed by the assembly of metal-containing units with organic linkers through coordination bonds or other weak interaction（such as hydrogen bonds,π-πinteraction,electrostatic interaction and van der Waals interaction,etc）.Based on the designability and tunability of metal ions/metal clusters,organic bridging ligands,coordination polymers possess excellent physical and chemical properties and specific functions for a wide range of applications in photoluminescence,photochromism,proton conduction,luminescence sensing and catalysis.Based on the principle of crystal engineering and function-oriented,this thesis focuses on the design and synthesis of coordination polymer materials with novel structure and excellent performance.Nitrogen carboxylic acid organic ligands possess rich electronic properties and flexible coordination modes.Meanwhile,the easy modifiability of nitrogen carboxylic acid ligands and the functional groups available are flexible and easy to be functionalized.They are widely used to construct coordination polymers with diverse structures and excellent performance,which have been the focus of scientific research.The research idea of this thesis is to design and synthesize nitrogen-containing carboxylic acid ligands based on functional orientation.By adjusting the reaction conditions（such as temperature,p H,solvent ratio,etc.）and selecting d¹⁰/d⁰ metal ions as inorganic building units,we obtained four coordination polymers with excellent optical properties.At the same time,we conducted physical characterization,properties analysis and mechanism exploration of the coordination polymers.The main research work of this thesis is summarized as follows:1.Synthesis,structure and study of photochromic properties of coordination polymers based on nitrogen carboxylic acid ligand.Synthesis of nitrogen-containing carboxylic acid ligands:and 4-carboxy-1-（4-carboxybenzyl）pyridinium bromide（H₂Ccbp Br）and N-（2-carboxyethyl）-4,4’-bipyrinium chloride（CPbpy Cl）were synthesized based on 4,4’-bipyridine and 4-pyridinecarboxylic acid by introducing chain and ring substituent groups.Three photochromic compounds[Zn（2,3-pydc）（H₂O）₂]_n（1）,{[Cd（Ccbp）₂]（H₂O）（DMF）}_n（2）,{[Cd（CPbpy）₂Cl]（NO₃）（H₂O）₃}_n（3）were constructed by hydrothermal and volatilization methods.Single-crystal X-ray diffraction analysis determined the structures of coordination polymers 1-3.The physical characterization and mechanism of the coordination polymers were investigated by PXRD,UV-vis,TG,IR,EPR,PL and XPS tests.The results showed that the photochromism of coordination polymers 1-3 are charge transfer type photochromism,and theπ-πinteraction between aromatic rings contributes to the stability of free radicals.In addition toπ-πinteractions between pyridine rings,hydrogen bonding interactions also exist in 1,which makes the radicals generated by photoinduced electron transfer occurring in 1 highly stable.The color of 1 after coloring can be maintained in dark environment at room temperature for more than 6 months.XPS results indicated electron transfer from O to N atoms.Theπ-πinteraction between the benzene and pyridine rings in 2 enhances the stability of radicals generated by photo-induced electron transfer from 2,which can also be maintained for more than 6 months at room temperature in the dark.XPS results showed electron transfer from the carboxyl O atom to the N atom of the pyridine ring.The stability of free radicals produced by photoinduced electron transfer of 3 is relatively poor,and the colored sample can fade within24 h.XPS results suggested that electrons are transferred from Cl atom to pyridine ring.Time-dependent photoluminescence spectra showed that 1-3 have potential applications in the field of photomodulated luminescence,and the fluorescence intensity of 1 and 3 increases with the increase of illumination time.It is worth mentioning that the fluorescence intensity contrast of3 before and after irradiation is up to 31 times,exceeding most reported photochromic coordination polymers.Cycle stability tests were performed on the photochromic behavior of3 for up to fourteen cycles.Based on the length of coloring and fading time of compounds 1-3,they can be applied to erasable inkless printing and anti-counterfeiting fields.2.Synthesis,structures and luminescence sensing properties of coordination polymer based on 3,5-bis（3’,5’-dicarboxyphenyl）-1H-1,2,4-triazole.Selecting 3,5-bis（3’,5’-dicarboxyphenyl）-1H-1,2,4-triazole（H₄L）with rich electronic properties and flexible coordination modes,and adjusted the p H of the reaction system.{[Ba（H₂L）（H₂O）_2.5]·H₂O}_n（4）with luminescence sensing properties were successfully constructed by hydrothermal method.The coordination polymer 4 exhibited a sensitive quenching response against Fe³⁺and nitrobenzene in aqueous solution(for Fe³⁺:K_sv=3.22×10³ M^-1;for nitrobenzene:K_sv=1.18×10³ M^-1).Based on the strong photoluminescence emission of 4 and its high stability in water,aqueous solutions of different p H values and different organic solvents,indicating that 4 can be a good luminescence sensor in aqueous systems.And is expected to be a luminescence probe for the detection of Fe³⁺and nitrobenzene in complex aqueous systems.The UV-vis absorption spectrum of Fe³⁺partially overlaps with the excitation and emission spectra of 4.The UV-vis absorption band for the Fe³⁺aqueous solution had a partial overlap with the excitation and emission spectrum of 4.Thus,the competition between the absorption band of the Fe³⁺and the excitation energy of 4,and the absorption of emitted luminescence were responsible for the luminescence quenching.The UV-vis absorption spectrum for the nitrobenzene aqueous solution had a partial overlap with the excitation spectrum of 4.The competition between the absorption band of the nitrobenzene and the excitation energy of 4 was responsible for the luminescence quenching.