The effects of substituting oxygen for terminal nitrogen in aniline oligomers 2: A DFT comparison of diamino, dihydroxyl, and monoamino/monohydroxyl terminated aniline trimers

The variant aniline trimers, N,N′-bis (3′,4′-diaminophenyl)-1,4-quinonediimine; N,N′-bis (3′-hydroxy-,4′-aminophenyl)-1,4-quinonediimine; and N,N′-bis (3′,4′-dihydroxyphenyl)-1,4-quinonediimine were synthesized, and the properties of the compounds compared to the results of density functional theory (DFT) calculations using the B3LYP functional. The calculations are complicated by the large number (five) of isomeric forms of each compound. Each compound energetically preferred the syn-, syn- (outer) isomer. The computed vertical ionization energies for the same isomer of each compound are 75.0, 76.10, and 83.1 kcal mol−1, respectively. The trimer with two oxygen atoms on each outer ring thus holds electrons more tightly than the trimers with either one or zero oxygen atoms on the outer rings. The electronic spectra computed by the ΔSCF method are in excellent agreement with experimental values, though inclusion of solvent effects does not improve the predictions. A red-shift upon change to more polar solvents confirms that the principal absorption band for each trimer is π → π*, in agreement with electronic structure calculations.