Synthesis And Stimuli-responsive Luminescence Properties Of Heterometallic Coordination Polymers

Recently,luminescent coordination polymers?LCPs?bearing stimuli-responsive properties,especially mechanical response property,have attracted much attention owning to their potential application in luminescence,sensors and anti-counterfeit materials.Up to now vast majority of such materials are based on single-emission,which are suffered from single signal response and easy interference.Herein we synthesized two heterometallic and dichromatic?2p-4f,3d-4f?LCPs based on H₂L?5-?1,3-dioxo-1H-benzo[de]iso-quinolin-2?3H?-yl?isophthalic acid?which contains a naphthalene group.The dihedral angle between aromatic groups in the ligand enables partial energy transfer between the ligand and Eu³⁺ion,leading to dual emission.The response of the compounds toward external stimuli was studied.Derails are described as below:?1?One-dimensional heterometallic Na-Eu LCP?1?was prepared based on H₂L ligand.The mechanical response experiment showed that the color of 1 changed from pink to blue under grinding,accompanying with a change from crystalline to amorphous.The ground phase could recover the original structure and luminescence upon soaked in DMSO.The temperature response experiments shows that 1 can be used as a ratiometric luminescent thermometer in the temperature range of 303.15-383.15 K.When T_m=323.15K,the maximum sensitivity S_m=2.765%·K^-1.The solvent response experiments indicates that 1can be used to recognize methanol and ethylene glycol by naked eye.In addition,we have established a 2D decoded map based on I_L:I_Eu³⁺?593 nm?and I_L:I_Eu³⁺?619 nm?to distinguish more solvents.The chromism mechanism of 1 may be due to the synergistic effect of two factors.One is the change of?...?interaction between neighboring ligands under grinding.Another is the lose of the solvent molecules under grinding.Both result in the change of the luminescence intensity of ligand and Eu³⁺.The combination of the two factors makes 1 a rare heterometallic dual-emission multi-responsive LCP material.?2?Heterometallic Zn-Eu compound?2?was prepared based on H₂L ligand.The mechanical response experiment showed that the color of 1 changed from faint pink to bright blue under grinding,accompanying with a change from crystalline to amorphous.Compared with that of 1,the mechanical response of 2 has a shorter response time but the ground phase can not be recovered.Solvent response experiments of 2 indicate that it can be used not only to recognize chloroform molecule by naked eye,but also to differentiate halogenated hydrocarbon solvents solvent molecules by a 2D decoded map based on I_L:I_Eu³⁺?593 nm?and I_L:I_Eu³⁺?621 nm?.Therefore 2 is a rare dual-emission 3d-4f heterometallic compound with dual stimuli-responsive.