Resonance Raman spectroscopic studies of the structure of electrogenerated short-lived radicals in solution by means of column-electrolytic continuous-flow method

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A column-electrolytic continuous-flow method has been developed for the measurement of time-resolved resonance Raman (RR) spectra of electrogenerated short-lived organic radicals in solution. The great feature of this method is t he ease of controlling the concentration of species, which makes the method a powerful tool for the RR study of electrogenerated intermediates in solution.The RR spectrum of the thianthrenecation radical was observed and its structure in the solution was (Liscussed. based on the assignment of the RR bands. The RR spectra of the oxidezed solutions of three aromatic amines were also measured. The spectra were assigned not due to those of cation radicals but to those of dimer cation radicals produced in the consecutive reactions.The selective observation of the RR spectra of electro-generated cation radical and dication of dimethy1diphenylbenzidine were carried out by controlling the electrolysis conditions and selecting the Argon ion laser excitation lines of 488.0 and 514.0 nm. The image-intensified multi-channel photo-diode arrey detector was utilized for the acquisition of time-resolbed RR spectrum of short-lived radicals. It was proved that the time-resolution of shorter than 100 ms could be achieved in the time-resolved measurement of electro-generated species.The RR spectra of the cation radicals of anthracene derivatives and the dications of benzidine derivatives have been successfully observed by using the kripton ion laser exitation of 647.1 nm, which is infavorable conditions for the Raman measurement.