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 SnO 2 surfaces from DMSO, CH 3 CN, and CH 2 Cl 2 . 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 (∼1100 nm) corresponding to diphenylbenzidine radical cation π-dimer in CH 2 Cl 2 whereas in DMSO and CH 3 CN at the same potential, no low-energy bands are observed. Variable-angle transmission spectroscopy on air-oxidized dry films prepared from CH 2 Cl 2 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 CH 2 Cl 2 . We interpret these spectra as arising from π-stacks parallel to the surface. Scanning electron micrographs show small domains (∼300−500 nm) for films composed mostly of dimers and smooth films for relatively higher molecular weight materials.