A series of 20 conjugated aromatic polyimines, containing p-phenylene, p-biphenylene, p-terphenylene, 4,4'-stilbene, and 1,5-naphthalene linkages in the backbone and various electron-donating and electron-withdrawing side-group substitutions, has been synthesized, characterized, and used to investigate the effects of molecular structure on the electronic structure and properties of conjugated polymers. Soluble gallium trichloride or diaryl phosphate complexes of the aromatic polyimines in organic solvents facilitated their solution spectroscopic ( NMR, UV-vis) characterization and their processing into thin films and coatings. The solid state electronic structure of the polymers was characterized by optical absorption spectroscopy and cyclic voltammetry of thin films. Electrochemical reduction of the aromatic polyimines was reversible with formal potential of -1.93 to -1.52 V (SCE) and 0.22 to 0.86 charge transferred, whereas oxidation was irreversible. The electron 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 associated 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 of 2.08-2.77 eV; the optical gap of thin films of gallium trichloride or 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 polyimines are an interesting class of -conjugated polymers whose electronic 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.

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