Synthesis And Photophysical Properties Of The Manganese (Ⅱ) Complexes Constructed From Phosphine Oxide Derivative-Based Ligands

Luminescent chromic materials have been intensively investigated and become one of the hot spots in current material research due to the comprehensive applications in molecular sensors,data storage,anti-counterfeiting and luminescent devices etc.Generally,luminescent chromism effect includes mechanochromism,thermochromism,and vaporchromism.The state of art material research focus on metal complexes containing d8/d10 noble metal ions such as Pt(Ⅱ),Ag(Ⅰ)and Au(Ⅰ).However,the employ of the expensive noble metal must obstruct the development and application of luminescent chromic material.Thus,the exploration of low-cost transition metal complexes with superior performance is imminent.Here,the luminescent chromic mechanism and performance of low-cost manganese(Ⅱ)complexes with phoshine oxide ligand are studied.1.A series of Mn(Ⅱ)metal complexes[MnBr2(dppeO2)]n(1),[MnBr2(dppeO2)(DMF)]n(la),[Mn(dppeO2)3][MnBr4](2),Mn2Br4(dppeO2)2(3)and[Mn(dppmO2)3][MnBr4](4)were synthesized based on dppeO2(ethane-1,2-diylbis(diphenylphosphine oxide))and dppmO2(methylenebis(diphenylphosphine oxide)),respectively.The photophysical properties containing the excitation spectra,emission spectra,lifetime and solid-state quantum yield were studied.Particularly,when green-emitting crystalline sample 1 was exposed to the solvent vapours with potential coordination ability such as DMF,H2O,methanol,ethanol,acetone,acetonitrile,THF and dioxane etc,obvious changes could be observed only for DMF,water and alcohol.The dramatic red-shift of the emission from 510 to 630 nm was caused by the conversion of manganese(Ⅱ)coordination geometry from tetrahedron to trigonal bipyramid via DMF coordination.The DMF-coordinated compound la could revert to DMF-free compound 1 companying with red to green emission conversion.2.One-dimensional chain polymer[MnBr2(pnpO2)]n(5)was prepared based on pnpO2(1,3-phenylenebis(diphenylphosphine oxide))ligand.With the temperature increasing from 80 to 440 K,the luminescence color changes from red(624 nm)to green(510 nm)under ultraviolet light irradiation.Green emission could revert to red emission as the temperature decrease from 440 to 80 K.DSC analysis showed two phase transition points at 299 and 404 K.Single-crystal X-ray diffraction demonstrated that the dramatic red-shift of the emission from 510 nm to 624 nm originated from the conversion of manganese(Ⅱ)coordination geometry from tetrahedron to trigonal bipyramid.The chain space decreased from high temperature to low temperature.In addition,the magnetic properties of the complexes were studied.3.Manganese(II)complexes[MnBr2(pbpO)2](6)and[MnBr2(dpppO2)]n(7)based on pbpO(5-phenyl-5H-benzo[b]phosphindole 5-oxide)and dpppO2(propane-1,2-diylbis(diphenylphosphine oxide))were synthesized.The structures were determined by single crystal X-ray diffraction.Under mechanical grinding,the dramatic red-shift of the emission from 513 to 620 nm for complex 6 and 510 to 611 nm for complex 7 were caused by the transition from crystalline to the amorphous,which was determined by the powder X-ray diffraction.It is likely that grinding or mechanical pressure reduced the bond distance between manganese(Ⅱ)and bromine on the adjacent structural units to produce weak bond interaction.The coordination structural change around manganese(Ⅱ)center from tetrahedronal to trigonal bipyramidal geometry thus results in the emission enhancement as well as large red-shift.