Photochromic Hybrid Materials Constructed With Oxalic Acid/phosphonic Acid And Their Photomagnetic Responses

Photochromic and photomagnetic materials,with the advantages of optical regulations of color variations,adjustable luminescence and magnetic properties,have great potential applications in the fields of information storage and molecular switch.It is still a major challenge in the field of photochromism to achieve the reversible regulations and photomagnetic coupling properties of chromic materials at room temperature.In this paper,oxalic acid/phosphonic acid were used as electron donors,polypyridine ligands were introduced as electron acceptors,a series of novel crystalline functional complexes were constructed with paramagnetic metals.Reversible photochromism,photomagnetic response and luminescence regulation under light conditions were realized in these complexes via electron transfer between electron donors and acceptors.The specific works are as follows:Firstly,twocompounds[Fe(C₂O₄)₃]·(H₃-TPB)·(H₂O)(1)and[Fe(C₂O₄)₃]·(H₃-TPA)·(H₂O)(2)were synthesized by respectively introducing2,4,6-tri(4-pyridine)benzene(TPB)and tri(4-pyridine)amine(TPA)polypyridine ligands into the iron oxalate systems via oxalic acid melting methods.Both compounds with different structures all show color changes from pale green to orange upon Xe lamp illumination.According to UV-vis absorption spectrum,fluorescence spectrum,IR and M(?)ssbauer spectrum analysis,part of central Fe³⁺are reduced to Fe²⁺during photochromic process,accompanied by the decomposition of oxalate ligands to produce CO₂and electron transfer to generate free radicals.The changes of photomagnetic response before and after irradiation was further studied,and the photomagnetic coupling between the photogenerated free radicals and magnetic metals was explored.After irradiation,the antiferromagnetic coupling effect shows clear enhancement in both compounds.Secondly,two compounds,[Ln₂(H₂-HEDP)₃(H-HEDP)]·(H₃-TPB)·x(H₂O)(Ln=3-Dy,x=8;3-Gd,x=11)and 3[Dy₂(H₂-HEDP)₄]·2(H₃-TPA)·2(H₄-HEDP)·10(H₂O)(4)were synthesized by hydrothermal methods with the addition of polypyridine ligands into the rare-earth phosphonate systems.The UV-vis absorption spectrum,electron paramagnetic resonance(ESR)and X-ray photoelectron spectroscopy(XPS)confirmed the photoinduced electron transfer happens in the rare earth phosphonates from phosphonic acid to polypyridine ligands and results in the photochromism.The study also shows that photogenerated free radicals could effectively improve the room temperature phosphorescence properties in 3 and 4.The antiferromagnetic coupling between photogenerated free radicals and rare earth metals was confirmed by magnetic tests for 3and 4 before and after irradiation.