Synthesis, electrooxidation, and characterization of bis(diphenylamine)naphthalene diimide

We have synthesized a new poly(imide) precursor for solution electrodeposition onto conducting surfaces. The new monomer, N,N'-bis[p-phenylamino(phenyl)]-1,4,5,8-naphthalenetetracarboxylic diimide (DNTD), contains a central naphthalene diimide moiety flanked by two dimerizable diphenylamine groups. DNTD was oxidatively electrodeposited onto Au-, Pt-, and In-doped SnO2 surfaces from DMSO, CH3CN, and CH2Cl2. The cyclic voltammetry is consistent with initial radical cation formation of diphenylamine groups, and then para C-C coupling of radicals to form dimers and higher order oligomers. IR spectroscopy was used to determine the average degree of polymerization and confirm para coupling. The resulting material shows electrochemically reversible 1e(-)/ and 2e(-)/monomer unit reduction waves corresponding to the naphthalene tetracarboxylic diimide radical anion and dianion. Also a quasireversible 1e(-)/ and 2e(-)/monomer unit oxidation corresponding to the oxidation of diphenylbenzidine unit is shown. Visible-NIR spectroelectrochemistry shows low-energy absorptions in the NIR (similar to 1100 nm) corresponding to diphenylbenzidine radical cation pi-dimer in CH2Cl2 whereas in DMSO and CH3CN at the same potential, no low-energy bands are observed. Variable-angle transmission spectroscopy on air-oxidized dry films prepared from CH2Cl2 shows band shifts from 1100 to 950 nm and almost no shift of the 845 nm band of films formed in DMSO. This is consistent with the anisotropic nature of the material from CH2Cl2. We interpret these spectra as arising from pi-stacks parallel to the surface. Scanning electron micrographs show small domains (similar to 300-500 nm) for films composed mostly of dimers and smooth films for relatively higher molecular weight materials.