NEW METHODS FOR THE ACCURATE DETERMINATION OF EXTINCTION AND DIFFUSION-COEFFICIENTS OF AROMATIC AND HETEROAROMATIC RADICAL-ANIONS IN N,N-DIMETHYLFORMAMIDE

Two electrochemical methods are presented that allow an easy access to highly accurate UV-visible spectra of aromatic and heteroaromatic rad ical anions with life times longer than 50 s in N,N-dimethylformamide. The uncertainty on the extinction coefficients obtained is estimated to be as low as 5% which is a significant improvement in accuracy comp ared with other methods. The study has involved the radical anions of benzophenone, fluorenone, 1,4-naphthoquinone, anthraquinone, 1,2-benza nthraquinone, (E)-stilbene, anthracene, 9,10-diphenylanthracene, fluor anthene, perylene, benzonitrile, p-tolunitrile, 1,4-diacetylbenzene, 1 ,4-dicyanobenzene, 9,10-dicyanoanthracene, (E)-azobenzene, (E)-4-metho xycarbonylazobenzene, quinoxaline and phenazine. The first method take s advantage of a galvanostatic generation of the radical anions from t he parent compounds combined with the recording of the absorbance at s pecific wavelengths by means of a so-called dip probe. The second tech nique described is based on the continuous and complete electroreducti on of the aromatic compounds in an efficient electrochemical flow cell placed just ahead of a quartz cuvette in a traditional diode-array sp ectrometer. The successful strategy of combining a galvanostatic gener ation of aromatic radical anions with the measurement of a characteris tic physical property has also been employed in the determination of d iffusion coefficients. The recording device is here a rotating disc el ectrode. (C) 1998 Elsevier Science S.A. All rights reserved.