RADICAL-ANIONS FROM SOME PHOTOCHROMIC NITROCOMPOUNDS - AN ELECTRON-PARAMAGNETIC-RESONANCE AND ELECTROCHEMICAL STUDY

Five 6'-nitrospiro[indole-benzopyrans] have been reduced electrochemic ally in ACN to the corresponding radical anions. Their reduction poten tials were in the range -1.32 to -1.40 V versus SCE, that is in the ra nge expected for substituted nitrobenzenes. The EPR spectra of the spe cies resulting from chemical reduction of the same compounds were also recorded, and suggested that the structure of the observed radicals v aries with the reduction media: thus, while the spectra in DMSO could be attributed to the radical anions structurally similar to the starti ng compounds, those observed in THF under UV irradiation were assigned to the anions of the open merocyanines. It appears that also the spec ies observed by reduction in DMF ought to be assigned the open structu re.