Studies Of Electron-Transfer Mechanism And Electrochromic Property For Viologen/Metalloviologen Compounds

Viologen is known as a functional organic compound which is consist of bi/multi-pyridine groups,and has been studies in multiple fields in recent years.Because of their excellent redox properties when stimulated by an external field(such as light,electric,heat,stress,water and others),they would show single-electron redox reaction with obvious color change.The charge-separation result for this kind of materials is clear,but the progress for the charge separation process is unclear which limited their development.The charge separation process of viologen is too very fast to be captured by some steady methods.Thus,prolong the lifetime of the charge separation process is beneficial for some steady analysis methods,and is important for applications in solar-energy conversion and others.In this research,the coefficient synthesis method of electron relay and steric effect was used to prepare two 4,4'-bipyridine based Zn(II)coordination compounds,one with big interannular dihedral and the other with small.Upon irradiation,the compound with smaller interannular dihedral turned from pale yellow state to purple state directly(< 1 s),which is similar to the phenomenons of reported viologen-based compounds.However,for the compound with bigger interannular dihedral,the charge separation process had been obviously decelerated.In the same irradiation condition,it turned from pale yellow to the yellow intermediated state at once(< 1 s),and then decayed to the normal purple state(about 1 day).The decelerated charge-separation process could be analyzed by some steady method,such as electron paramagnetic resonance,UV-vis-NIR diffuse reflection and Raman spectra.According to these spectroscopy analysis methods,after irradiation,the charge has been transferred to Zn and its surrounding and the yellow intermediated state which consist of Zn(I)and organic radical was obtained.Then,the charge on Zn(I)transferred to 4,4'-bipydine,and the purple viologen radicals were produced.As for the classical viologen-based compound,the previously unknown photoinduced yellow partially charge separated(PCS)state was captured.At the same time,the photochromic reaction is almost limited on surfaces through UV-vis induced method which makes the detection of structure variation difficult.In this research,enough amounts of photochromic products could be produced by the penetrating X-ray(Cu-K?)source without significant structural damage.And the single-to-crystal-to-single-crystal structural evolution process of viologen analog in the photochromic process was first captured by the X-ray diffraction method.The structure analysis shown that the planarity of 4,4'-bipyridine(bipy)was decreasing with the charge-separation process was going on.With the associated effect of electron relay and the interannular dihedral of bipy,the charge separation process was decelerated which is hopeful to enrich the applications for some electron-transfer compounds.This research focuses on the electron transfer mechanism,has captured the photoinduced charge separation state with lifetime of second scale for the first time through resolve resolution.And this research has verified the charge separation mechanism of photochromic process,which provided design strategy for multicolor photochromism and improving the light-energy efficiency or other applications.Researched on 4,4'-bipyridine-based electrochromic compounds have been studied widely.The most studied is the electrochromic properties of N,N'-mono/di-substituted bipyridium,which were prepared by changing the substituting of alkyl or phenyl groups on N atom to fabricated electrochromic materials with different properties.However,the color states of these bipyridiums are very shortage,the fabricated strategy is complex and the stability of the electrochromic devices(ECD)are hard to be promoted in the liquid state.Therefore,the development of easy-to-prepare films and the color types of electrochromic materials are long-term problems to be solved.This study has designed a series of new viologen-based photochromic compounds with film-fabrication properties.The electrochromic property could be estimated through the photochromism,and the electrochromic device with film-forming properties and rich color is obtained.