Stable Photoinduced Separated Charge State in Viologen Halometallates: Some Key Parameters

With the aim to define key parameters causing the photochromic properties of (MV)[Bi2Cl8] and (MV)4[Bi6Cl26] (MV2+, methylviologen; 1,1′-dimethyl-4,4′-bipyridinium), the effects of substituting Bi by Sb, Cl by Br, or MV2+ by MOV2+ (1,1′-dimethoxy-4,4′-bipyridinium) or MeMOV2+ (1-methyl-1′-methoxy-4,4′-bipyridinium) on the photoinduced charge transfer properties of such viologen halometallates are explored. It appears that only salts containing chlorobismuthate anions undergo a color change upon UV irradiation and that the nature of viologen entities has a key role in the process. We also suggest that a key parameter for observing the stable photoinduced separated charge state in chlorobismuthate viologen hybrids is a high chloride/viologen ratio, rather than the size of the anionic oligomer, as observed in the previously reported unique series (MV)(2n+2)/2[Bi2nCl8n+2].