Synthesis And Luminescence Properties Of Tunable Luminescence Pyridine Imine Metal Complexes

Transition metal Schiff base complexes have been recurrent themes and recieved more attentions in synthetic coordination chemistry due to their wide applications in luminescence,sensors,catalysis and biological chemistry,etc.In this work,thirteen kinds of ligands were obtained from a typical condensation reaction(monamine with pyridine aldehyde derivatives).Using these Schiff base ligands,twenty-six Zn(II)/Cd(II)/Hg(II)complexes have been successfully synthesized.The structures of these twenty-six complexes have been confirmed by X-ray single-crystal analysis and further physically characterized by elemental analysis(EA),FT-IR,1H NMR spectra,and powder XRD(PXRD).A systematic work is discussed on the effects of substituent groups and anions on the supramolecular frameworks and luminescent properties.Four kinds of Zn(II)/Cd(II)complexes,[ZnL1Cl2]2(Zn1),[ZnL2Cl2](Zn2),[Zn3(L1)2(OAc)6](Zn2?),[CdL1(OAc)2](Cd2),have been synthesized from the corresponding(E)-N-(pyridine-2-yl)(CH=NPhR)(where R = 4–NO2,L1;4–CH3,L2)Schiff base.Zn2? and Cd2 are multinuclear complexes may be due to the chelation of OAc–.The absorption and emission bands of the complexes of L2 are red-shifted compared to that of L1,which is consistent with the electron-donating ability(–CH3 > –NO2)of substituents.These complexes show blue luminescence emissions in the range of 461 nm – 489 nm.Zn2? and Cd2 exhibit obvious aggregation-induced emission enhancement(AIEE)properties in the CH3CN–H2O mixture solutions.A series of methyl substituted of Zn(II)complexes,[Zn L3Cl2](Zn3),[ZnL4Cl2](Zn4),[ZnL5Cl2](Zn5),[ZnL6Cl2](Zn6)((E)-N-(pyridine-2-yl)(CMe=NPhR),where R = H,L3;2–CH3,L4;2,6–(CH3)2,L5;2,4,6–(CH3)3,L6)have been synthesized.The crystal structures indicate that the numbers of methyl can directly infect the formation of 1D ? 3D supramolecular frameworks(3D,Zn3;2D,Zn4 and Zn5;1D,Zn6)via C-H···Cl/? hydrogen bonds and ?···? interactions.Based on these varied structures caused by different methyl substitutions,the maximum emission wavelengths of complexes Zn3–Zn6 can be tuned in the range of 472 nm – 514 nm.Density functional theory calculations show the electronic properties of the complex molecule are in line with the spectral data.A series of M(II)(M = Zn,Cd,Hg)complexes,[M(L7~L12)Cl2](Zn7–Zn12,Cd11,Cd12,Hg7–Hg12,except for [CdL10Cl2]2,Cd10)and [Zn(L12)2]?(ClO4)2(Zn12?)have been synthesized from the corresponding(E)-N-(6-methoxypyridin-2-yl)(CH=NPhR)(where R = H,L7;2–CH3,L8;2,4,6–(CH3)3,L9;2,6–i(C3H7)2,L10;4–CH3,L11;2–OCH3,L12)Schiff base.The larger steric hindrance and atom radius(Zn(27)Cd(27)Hg)are disadvantageous in forming of the higher dimension supramolecular frameworks.Upon the irradiation of UV light,the maximum emission wavelengths of these complexes could be finely tuned from green(480 nm-540 nm)in the solid state to blue(402 nm-425 nm)in acetonitrile solution.Zn9,Zn11 and Zn12 were employed to prepare cosensitized dye-sensitized solar cells devices for investigating the influences of the electron-donating group on the DSSCs performance.Compared to the DSSCs only sensitized by N719,these prepared complexes were chosen to cosensitize N719 in solar cell do enhanced its performance by 10.2%-35.8%.Moreover,the luminescence intensities(18-fold)and thermal stability(98 oC)of Zn12? is increased after doped with PMMA.Therefore,the PMMA doping with the luminescent d10 metal complexes may be of potential application as light–emitting materials.A new simple ‘dual' chemosensor L13((E)-2-Methoxy-N-((quinolin-2-yl)-methylene)aniline)for distinguishing Zn2+ and Hg2+ has been designed and synthesized.The sensor showed the excellent selectivity and sensitivity with a fluorescence enhancement to Zn2+/Hg2+ over other commonly coexisting cations in DMSO–H2O solution(1/99 v/v),which was reversible with the addition of ethylenediaminetetraacetic acid(EDTA).The detection limit for Zn2+/Hg2+ by L13 both reached 10–8 mol L–1 level.The 1:1 ligand-to-metal coordination pattern of the L13-Zn2+ and L13-Hg2+ were calculated through a Job's plot and ESI-MS spectra,and complexes Zn13 and Hg13 were further confirmed by X-ray crystal structures.This chemosensor can recognize similar metal ions by coherently utilizing intramolecular charge transfer(ICT)and different electronic affinities of various metal ions.DFT calculations have revealed that the energy gap between the HOMO and LUMO of L13 has decreased upon coordination with Zn(II)/Hg(II).The solid state luminescence spectra of complexes Zn13 and Hg13 show yellow luminescence emissions(571 nm,Zn13;541 nm,Hg13).