EXCITATION WAVELENGTH DEPENDENCE OF THE Z-]E ONE-WAY ISOMERIZATION OF4-HALOSTILBENE RADICAL CATIONS IN EXCITED-STATES

Excitation of (Z)-4-halostilbene radical cations ((Z)-XSt(+); X = F, C l, Br) around 500 or 700 nm induced their rapid one-way isomerization to the corresponding (E)-radical cations, as observed in two-color pul sed laser photolysis of (Z)- and (E)-XSt in acetonitrile containing 9, 10-dicyanoanthracene and biphenyl as electron-transfer sensitizers. Th e efficiencies of isomerization and quenching by biphenyl as electron donor are discussed on the basis of the electronic configurations and energy surfaces of the relevant excited states.