Erjian Wang

Photoinduced electron transfer in the ion pair compound (XTOn): influence of ionic association

Abstract The influence of the ionic dissociation equilibrium on the photochemical and photophysical properties of xanthene dye onium salts (XTOn) was studied. The dissociation constants (KD) determined by conductivity verify that the ionic association states directly influence the changes in the absorption spectral shape, and the ratio I532/I445 reflects the degree of dissociation of the system. The results of static v fluorescence quenching and dynamic lifetime quenching experiments demonstrate that the electron transfer of XTOn is mainly intra-ion pair electron transfer; the quenching rate constants of intra-ion pair electron transfer approach 1012–1013 s−1 M−1, which is well above the rate limit controlled by diffusion. The effects of substituents and solvents show that the process of electron transfer is controlled by the degree of association, and the efficiency of photosensitized initiation may be improved further by a shift in the equilibrium.

A novel pathway to photoinduced colour formation of colourless flourane dye using iodonium salts as activators

Abstract A photoinduced colour formation system consisting of flourane dye (FR) and iodonium salt was investigated. The thermodynamic data indicate that the photoreaction of colour formation mainly accurs via an electron transfer pathway. The processes of electron transfer colour formation were proposed by separating and analysing the photoproducts. On irradiation, the excited flourane dye and iodonium salt may undergo electron transfer to give a flourane radical (FR·+) and diphenyliodonium radical (·IPH2). The latter rapidly decomposes to a phenyl radical (Ph·) and iodobenzene, and the ring-opened coloured forms may be subsequently created via two pathways: abstraction of hydrogen by the FR·+ radical intermediate or coupling between FR·+ and Ph·. The acidic ring-opened coloured form from the abstraction of hydrogen is predominant, and easily undergoes a colour disappearance reaction in non-polar solvents or basic medium, but the structure of FR-Ph from radical coupling possesses good stability. In order to improve the solubility of the iodonium salt, several diaryliodonium salts containing different flexible phenolic chains or counterions were used as activators. The influences of these two factors on colour formation were studied; the results demonstrate that the former has no distinct effect on the rate of colour formation or maximal optical density at 580 nm, whereas the latter has a significant effect. The influence of concentration was also studied.

Synergetic effects of amines on the intra-ion-pair electron transfer dye photosensitization system Eo(IPh2)2

Abstract Stationary and transient spectroscopic studies on the eosin bis(diphenyliodonium) salt/triethylamine (Eo(IPh 2 ) 2 /TEA) system were carried out in comparison with Eo(IPh 2 ) 2 alone. In non-polar solvents where Eo(IPh 2 ) 2 forms contact ion pairs. TEA molecules insert themselves between the anions and cations, resulting in the formation of amine-separated ion pairs. When exposed to visible light, Eo(IPh 2 ) 2 / TEA undergoes oxidative electron transfer firstly. Synergetic effects of amines on Eo(IPh 2 ) 2 were found for which a cyclic regenerative mechanism was proposed. Eo(IPh 2 ) 2 /TEA was applicable for various monomers and unsaturated oligomers, especially of the acrylate type, even in the presence of oxygen. Concentration effects of Eo(IPh 2 ) 2 , amine and monomer were also investigated.

Electron transfer coloration of fluorane leuco dyes with iodonium salt—an approach for color stabilization

Abstract A thermocoloration system consisting of a fluorane leuco dye (FR) and an iodonium salt (DPIOB) was investigated. The color for the FR/DPIOB system posseses a highly colored stability. The rates of the color development reaction show a rapid rise with increase in temperature, and, owing to two kinds of different activation energy (E a ) at the range of reaction temperature in the polymeric film, the reaction easily occurs in the high temperature region (>104°C). The thermal susceptibility increases with increase of FR/DPIOB content. A mechanism of thermocoloration via an electron transfer process is proposed. FR is oxidized to the FR +• radical, the iodonium cation is reduced to the diphenyl iodine radical, which then rapidly decomposes to iodobenzene and the phenyl radical. The ring opened cationic ester (FR-Ph) is formed by radical coupling between FR +• and the phenyl radical.

New initiation system for holographic recording material

Some p-N,N-dimethylamine and diethylamine substituted benzal ketone derivatives (ABK) are used as a new class of sensitizer for laser light induced radical photopolymerization of N-vinyl carbazole (NVC) and methacrylic acid benzal ester (MABE) by combination with diphenyliodonium salt (DPIO). The relative efficiency of various ABK for polymerization of NVC and MABE to record holograms is in the order DEBP>DABA>ABA. An argon ion laser (488 nm) is used for exposure .Trichromatic filters were made with the material.