A Pulse Radiolysis Study of the Leucocyanide of Malachite Green Dye in Organic Solvents

Article abstract of DOI:10.1021/j100266a041

Microsecond pulse radiolysis studies have been carried out on the leucocyanide of malachite gree dye (MGCN) dissolved in either 1,2-dichloroethane, chloroform, carbon tetrachloride, acetone, cyclohexane, benzene, toluene, dimethyl sulfoxide, N,N-dimethylformamide, methanol, 2-propanol, tetrahydrofuran, dioxane, benzonitrile, or acetonitrile.The transient absorption spectra obtained in argon-saturated solutions, and with various added electron scavengers (N2O, O2, or CCl4), indicate that there are everal intermediate species and radiolytic products.We suggest that one product is the carbonium ion (MG⁺) of malachite green dye (wavelength of the absorption maximum, λ_max = 620 nm) and the other 4,4'-bis(dimethylamino)-triphenylmethyl radical (MG radical, λ_max = 400 nm).There is evidence for the formation of an intermediate primary radical cation (MGCN⁺) and a triplet excited state of malachite green cyanide.In oxygen-depleted solutions the absorbing species with λ_max at 620 nm is formed in a fast process completed within the time of the 5,5-μs pulse.However, only in 1,2-dichloroethane solution is this absorption stable during the observation time, whereas in all the other solvents it is unstable and decays within tenths of microseconds, the decay time depending of the solvent.In polar solvents such as Me2SO, DMF, alcohols, and acetonitrile, in the presence of oxygen, formation of the 620-nm absorption takes place in two kinetically distict processes.The first is very fast (much shorter than the 5,5-μs pulse) and the second much slower (lasting tens of microseconds after the pulse).Possible mechanisms for the fast and slow components of radiolytic dye formation are postulated.