ELECTROCHEMICAL STUDY OF THE PI-ASTERISK PROBE DYE 5-NITRO-5'-DIMETHYLAMINO-2,2'-BISTHIOPHENE

Cyclic voltamograms of the solvatochromic dye 5-nitro-5'-dimethylamino -2,2'-bisthiophene (1), introduced recently as a sensitive pi probe, were recorded in different solvents. An EPR spectrum of the anionic ra dical of 1 in DMSO was obtained and compared with other spectra of ana logous substituted bisthiophene radicals. It was found that the presen ce of a donor-acceptor pair of substituents in 1(-.) reduces significa ntly the rotational barrier of the radical compared with the unsubstit uted bithienyl radical anion 2(-.). This is the result of an electroni c repulsion between the donor ring fragment and the added electron in the coplanar radical, which does not exist in 2(-.). (C) 1998 John Wil ey & Sons, Ltd.