PHOTOCHROMISM OF VIOLOGEN HEXACYANOFERRATE(II) COMPLEXES VIA INTRAMOLECULAR ELECTRON-TRANSFER

Viologen metal complexes comprising 2,2'- and 4,4'-bipyridinium hexacy anoferrate(II) were synthesized starting from the corresponding halide s by an anion-exchange reaction. The charge-transfer bands appeared in aqueous solutions, whereas radical cation peaks in visible region app eared in solid polymer matrices via a photoinduced electron transfer w ithin the viologen molecule; their absorptions were dependent upon bot h the kind of bipyridinium dication and the media, such as the solvent s and polymer matrices. The reversible redox reaction by photon mode ( color development) and by heat mode (bleaching) can be repeated in the absence of atmospheric oxygen.