Bipyridinium Polymers That Dock Tetrathiafulvalene Guests in Water Driven by Donor–Acceptor and Ion Pair Interactions

Two water‐soluble para ‐xylylene‐connected 4,4′‐bipyridinium (BIPY 2+ ) polymers have been prepared. UV‐Vis absorption, 1 H NMR spectroscopy, and cyclic voltammetry experiments support that in water the BIPY 2+ units in the polymers form stable 1:1 charge‐transfer complexes with tetrathiafulvalene (TTF) guests that bear two or four carboxylate groups. These charge‐transfer complexes are stabilized by the donor–acceptor interaction between electron‐rich TTF and electron‐deficient BIPY 2+ units and electrostatic attraction between the dicationic BIPY 2+ units and the anionic carboxylate groups attached to the TTF core. On the basis of UV‐Vis experiments, a lower limit to the apparent association constant of the TTF⋅BIPY 2+ complexes of the mixtures, 1.8×10 6   m −1 , has been estimated in water. Control experiments reveal substantially reduced binding ability of the neutral TTF di‐ and tetracarboxylic acids to the BIPY 2+ molecules and polymers. Moreover, the stability of the charge‐transfer complexes formed by the BIPY 2+ units of the polymers are considerably higher than that of the complexes formed between two monomeric BIPY 2+ controls and the dicarboxylate‐TTF donor; this has been attributed to the mutually strengthened electron‐deficient nature of the BIPY 2+ units of the polymers due to the electron‐withdrawing effect of the BIPY 2+ units.