CONJUGATED AROMATIC POLYIMINES .2. SYNTHESIS, STRUCTURE, AND PROPERTIES OF NEW AROMATIC POLYAZOMETHINES

A series of 20 conjugated aromatic polyimines, containing p-phenylene, p-biphenylene, p-terphenylene, 4,4'-stilbene, and 1,5-naphthalene lin kages in the backbone and various electron-donating and electron-withd rawing side-group substitutions, has been synthesized, characterized a nd used to investigate the effects of molecular structure on the elect ronic structure and properties of conjugated polymers. Soluble gallium trichloride or diaryl phosphate complexes of the aromatic polyimines in organic solvents facilitated their solution spectroscopic (H-1 NMR, UV-vis) characterization and their processing into thin films and coa tings. The solid state electronic structure of the polymers was charac terized by optical absorption spectroscopy and cyclic voltammetry of t hin films. Electrochemical reduction of the aromatic polyimines was re versible with formal potential of -1.93 to -1.52 V (SCE) and 0.22 to 0 .86 charge transferred, whereas oxidation was irreversible. The electr on affinity and ionization potentials of the series of polymers varied from 2.46 to 2.94 eV and from 4.80 to 5.38 eV, respectively. The asso ciated LUMO and HOMO energy levels are thus tunable by up to 0.48 and 0.58 eV, respectively. The electrochemically and optically determined LUMO-HOMO energy gaps of thin films were very close and in the range o f 2.08-2.77 eV; the optical gap of thin films of gallium trichloride o r diaryl phosphate complexes of the polyimines was smaller and in the range of 1.66-2.14 eV. The results of this study show that aromatic po lyimines are an interesting class of pi-conjugated polymers whose elec tronic structure and properties can be regulated over a wide range by variation in backbone structure, side group substitution, and through intramolecular hydrogen bonding or complexation, backbone planarity.