Design and synthesis of bipyridyl-containing conjugated polymers: Effects of polymer rigidity on metal ion sensing

Three conjugated polymers comprised of 9,9-dioctylfluorene and 2,2'-bipyrid ine, which are alternatively linked by the C-C single bond (Pl), vinylene b ond (P2), or ethynylene bond (P3), have been synthesized via the Suzuki rea ction, the Wittig-Horner reaction, and the Heck reaction, respectively. The optical, electrochemical, and other physical properties of the polymers ar e dependent on the linkers. The polymer linked by the C-C single bond exhib its a much larger Stokes shift compared with the other two polymers, indica tive of higher extended and rigid backbone conformations in the polymers li nked by the vinylene and ethynylene bonds. All the three polymers are sensi tive to the existence of a variety of transition metal ions due to the chel ation between the 2,2'-bipyridyl moieties and the metal ions. For the metal ions which have moderate and weak coordination ability with the 2,2'-bipyr idyl moieties, an obvious difference in response sensitivity is observed am ong the three polymers: P1 has the highest sensitivity, which is followed b y P2, and P3 always exhibits the lowest sensitivity. The different sensing sensitivity is attributed to the different backbone rigidity of the three p olymers, which is caused by the three different linkers. The results sugges t the use of C-C single bond linker in the molecular design toward the 2,2' -bipyridyl-based conjugated polymer chemosensors for achieving higher sensi ng sensitivity.