Construction And Characterization Of A New Photochromic And Fluorescent Molecular System Based On Metal Coordination Complexes

Photosensitive molecular system plays an important role in the application of X-ray detection,gas sensing,rubbing printing,optical information storage and fluorescence switch.Due to low thermal stability of photosensitive organic moleculesr,great interest has been focused on the development of photosensitive molecular system based on metal-ligand complexes recently.These molecular systems involving electron transfer have the virtues of good thermal stability,convenient synthesis process and so on.The photo-response molecular system can be assembled by metal ions and traditional photochromic units or nonphotochromic units.In this paper,three photochromic materials constructed by photochromic units and two photo-response complexes constructed by nonphotochromic unites are prepared and their photochromism,fluorescence and electron transferproperties are characterized.1.the HCPBPy(N-(3-carboxyphenyl)-4,4'-bipyridinium chloride)is used as the electron acceptor block,while 1,5-naphthalenedicarboxylic acid is used as the electrondonor unit.A photochromic complex with interpenetration structure [Cd(CPBPy)(naphthalene-1,5-dicarboxylate)] · 2H2 O 1 was synthesized by solvothermal method.Under light irradiation,electron transfer reaction takes place from the electron-rich carboxylic group to the electron-deficient HCPBPy unit,forming photo-generated free radicals and resulting color changes of the complex.Due to the overlap regions of diffuse reflection absorption and the fluorescence emission,the energy resonance transfer causes fluorescence quenching.2.Two host-guest photo-sensitive complexes [Zn3(MV2+)(L4-)2] · 2H2 O 2,[Cd3(MV2+)(L4-)2(H2O)2]·2H2O 3 were constructed by introducing methyl viologens as a template(MV2+)and 5-((3,5-dicarboxybenzyl)oxy)isophthalic acid(H4L)molecule as flexible ligand.Two different framework structures are generated due to the coordination modes of connected ligands and the metal ions..Under ultraviolet or visible light irradiation,the color of compound 2 changes from khaki to dark green,while that of compound 3 changes from bright yellow to grass green,which are accompanied with fluorescence quenching at the same time.The coloration rate of compound 2 is much faster than compound 3 by the comparison of their photochemical reaction rate values.The color and fluorescence are restored when the colored sample is placed in dark at room temperature.Interestingly,the photosensitive crystal exhibits a high degree of stability and good reversibility in its photochromic behavior and fluorescence property over repeating cycles.3.Two supramolecular molecular systems {Zn1(PYTPY)(1,3-dioxo-1H,3H-benzo[de] isochromene-6,7-dicarboxylic acid)2}·H2O 4,{[Zn(HPO4)(PYTPY)]2·(H4BTEC)2}·H2O 5 are constructed by nonphotochromic nitrogen containing macrocyclic conjugated ligands and carboxylic acid ligands via hydrothermal approach.Different from previous charge transfer photoactive complexes showing photoinduced coloration from yellow to blue,yellow to black and yellow to red,these new donor–acceptor materials display new color response ranges.Under UV irradiation,the color of compound 5 changes from gray to orange and the charge-separated state stabilizes at room temperature for more than 3 months.