Synthesis and chemical properties of electrochromic π‐conjugated polyphenylenes with pendant viologen‐TCNQ salts

Polyphenylene (PP) with NH 2 side groups, namely, PFluNH 2 , was synthesized by the Pd‐catalyzed reaction of 2,5‐dibromoaniline with 9,9‐dihexylfluorene‐2,7‐diboronic acid bis(1,3‐propanediol) ester. The reaction of PFluNH 2 with 1‐hexyl‐1′‐(2,4‐dinitrophenyl)‐4,4′‐bipyridinium diiodide ( SaltBPy(I − ) ) eliminated 2,4‐dinitroaniline to yield PPs with viologen (1,1′‐disubstituted 4,4′‐bipyridinium dications), PFluBPy(I − ) . The reaction of PFluBPy(I − ) with Li + TCNQ − resulted in anion exchange between Cl − and TCNQ − , and yielded PFluBPy(TCNQ − ) . The reaction of PFluBPy(TCNQ − ) with the neutral TCNQ 0 resulted in an interaction between TCNQ − and TCNQ 0 , and yielded PFluBPy(TCNQ − ‐TCNQ 0 ) . Cyclic voltammetry measurements suggested that an electrochemical reduction of the viologen moiety and oxidation of the polymer backbone within PFluBPy(TCNQ − ) and PFluBPy(TCNQ − ‐TCNQ 0 ) . Furthermore, this reaction was accompanied by electrochromism. The electric conductivities (σ) of the pellets molded from PFluBPy(TCNQ − ) to PFluBPy(TCNQ − ‐TCNQ 0 ) were 2.7 × 10 − 4 and 4.2 × 10 − 4 Scm − 1 , respectively; these σ values were higher than that observed for PFluNH 2 (σ < 10 − 8 Scm − 1 ) due to the self‐doping in the polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013