POLY(1,5-NAPHTHYRIDINE-2,6-DIYL) HAVING A HIGHLY EXTENDED AND ELECTRON-WITHDRAWING PI-CONJUGATION SYSTEM - PREPARATION, OPTICAL-PROPERTIES, AND ELECTROCHEMICAL REDOX REACTION

Dehalogenation polycondensations of 2,6-dichloro-1,5-naphthyridine with isolated zerovalent nickel complex and electrochemically generated zerovalent nickel complex afford pi-conjugated poly(1,5-naphthyridine-2,6-diyl) (P(2,6-N)) in high yields. The electrochemical polymerization gives the polymer as a thin film on the electrode. UV-visible data indicate that P(2,6-N) has, among poly(naphthalene)like pi-conjugated polymers, the longest effective pi-conjugation system along the polymer chain due to its less sterically hindered structure to form the pi-conjugation system. Electrochemical reduction of P(2,6-N) takes place at E degrees = -1.79 V vs Ag/Ag+, the value revealing that P(2,6-N) belongs to the most easily reducible pi-conjugated conducting polymers reflecting a very strong pi-electron-deficient nature of the 1,5-naphthyridine ring. As for poly(naphthalene-2,6-diyl)-type polymers, introduction of every imine nitrogen leads to a shift of the reducing potential to the positive side by 0.3-0.4 V, Chemically reduced (or n-doped) P(2,6-N) with sodium naphthalide gives a dark blue adduct, which exhibits electrical conductivity of 1.8 x 10(-2) S cm(-1). The electrochemical reduction of a cast P(2,6-N) film causes a color change with the appearance of a new broad adsorption band in a near-infrared region.