ELECTROCHEMICAL AND CHEMICAL PREPARATION OF LINEAR PI-CONJUGATED POLY(QUINOLINE-2,6-DIYL) USING NICKEL-COMPLEXES AND ELECTROCHEMICAL PROPERTIES OF THE POLYMER

Dehalogenation polycondensations of 2,6-dichloroquinoline with electrochemically generated zerovalent nickel complex and isolated zerovalent nickel complex afford pi-conjugated poly(quinoline-2,6-diyl) (P(2,6-Q)) in high yields. Comparison of the polymerizations using various dihaloquinolines and dihaloisoquinolines as the monomer reveals that the electrochemical polymerization is more sensitive to the position of halogen in the monomer than the chemical polymerization and proceeds most smoothly for 2,6-dihaloquinoline. The electrochemically and chemically prepared P(2,6-Q)'s have molecular weights of 26 000 and 15 000, respectively, as determined by a light scattering method, which also reveals that P(2,6-Q)'s have a linear rodlike stiff structure with rho(v) values of 0.21 and 0.20, respectively, and a large specific refractive index increment (Delta n/Delta c = 0.57 cm(3) g(-1)) in formic acid. The electrochemical method gives the polymer as a thin film on the electrode. The cyclic voltammogram of the film of P(2,6-Q) shows a reversible electrochemical n-type doping-undoping cycle at considerably higher potential (ca. -2.1 V vs Ag/Ag+) than that of isomeric poly(quinoline-5,8-diyl), with a reversible color change of the film between yellow (undoped) and dark blue (doped); n-doping with sodium naphthalide also gives an electrically conducting dark blue adduct. UV-visible as well as cyclic voltammetric data suggest that P(2,6-Q) has a longer effective pi-conjugation system along the polymer chain than other isomeric poly(quinolinediyl)s and poly(isoquinolinediyl)s due to its less sterically hindered structure to form the pi-conjugation system. The electron affinity of P(2,6-Q) is estimated as 3.3 eV.