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

With the aim to define key parameters causing the photochromic properties of (MV)[Bi 2 Cl 8 ] and (MV) 4 [Bi 6 Cl 26 ] (MV 2+, methylviologen; 1,1′-dimethyl-4,4′-bipyridinium), the effects of substituting Bi by Sb, Cl by Br, or MV 2+ by MOV 2+ (1,1′-dimethoxy-4,4′-bipyridinium) or MeMOV 2+ (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) (2 n +2)/2 [Bi 2 n Cl 8 n +2 ].