Structures And Photochromic Properties Of Silver(?) Complexes Assembled With A Closed-form Dithienylethene Ligand

The dithienylethene compounds have been cited as the best candidates of photochromic materials for practical application due to their excellent characteristics.Using dithienylethene molecules as ligands and introducing metal ions to generate metal complexes with multiple structures is a common methods to adjust the photochromic properties.The introduction of metal ions can adjust the photochromic properties,such as shifting the maximum absorption wavelength,enhancing the photoreaction conversion rate and shortening the photo-reaction time;It can also offer the complex new multi-functional characteristics,such as photoluminescence,light-driven molecules/ion recognition,photoelectricity/magnetism,light-induced gas adsorption-desorption.In this paper,three different photochromic complexes were successfully synthesized(i.e.complex 1,complex 2 and complex 3)by using closed-BM-4-CP-3-TP(Lc)with cyano groups as ligands and three kinds of silver salts with different coordination abilities(AgCF3COO,AgCF3SO3 as well as AgBF4)as metal salts.The structures of these complexes were analyzed and characterized by IR,EA,1HNMR and MS.The molar absorption coefficient of the ligand Lc in the liquid phase,the conversion rate of the ring-closing reaction and the kinetic process of the photo-chemical reaction were studied.The ultraviolet-visible spectra were used to instigate the photochromism of three complexes in the liquid phase,PMMA films and solid phase.The photo-fatigue properties were tested in PMMA films.Their electrochemical propeities were further analyzed by the three-electrode method.The main conclusions are as follows:(1)The molar absorption coefficient of closed-ring Lc is determined as ?c=1.07×104 L·mol-1·cm-1 and that of open-ring Lo is ?o=5.17×103L·mol-1·cm-1 by UV-Vis spectra.The conversion ratio of ring-closing reaction is calculated as 48.3%and conversion ratio of the ring-opening reaction is 85.2%.(2)The reaction kinetics study showed that when irradiated with a specific intensity of light,the ring-opening reaction of closed-BM-4-CP-3-TP in solution belongs to the first-order reaction,the closed-loop reaction of BM-4-CP-3-TP in solution belongs to the zero-order reaction(3)UV-Vis spectra indicated that three complexes show reversible photochromism in both solution and PMMA films.Fatigue testing of theses complexes in PMMA films suggested their good fatigue resistances.There were no significant changes in intensities of absorbance after 20 cycles of photo-isomerizations(4)Solid-phase UV-visible spectra illustrated the reversible photochromic properties of complexes 1-3.The introduction of silver ions did not prevent the photochromism of the ligand In comparison with the ligand,the maximum absorption wavelengths of three complexes have no obvious shifts however the reaction time are decreased(5)Electrochemical tests inferred that the open-ring isomers of both ligand and complexes have higher oxidation potentials than those of the corresponding closed-ring isomers Complexes with different types of anions have different energy gap values.Complex 2,which is prepared by anion with moderate coordinating ability,has the smallest energy gap value.