Substituents Effect on the Electronic Properties of Aniline and Oligoanilines

Abstract

Aniline oligomers have been intensively studied in the past years. In particular, aniline oligomers substituted with electron-donor groups have been synthesized and its electronic properties calculated. However, when an electron-acceptor group is attached to the benzenoid ring of the oligoaniline, strong effects over its electronic properties are expected to happen. In this work some semiempirical quantum chemistry calculations of geometric structures, and energy level distribution of aniline and substituted anilines and its corresponding oligomer are presented. Geometry calculations of aniline and oligoanilines have been performed by using the PM3 and AM1 methods. Energy calculations and UV−vis spectra have been done by using the ZINDO/S-CI method. The studied substituents are methoxy, methyl, fluorine, nitro, and cyano groups, located at positions 2 or 3, in the benzenoid ring. This series of substituent groups involves a large range of σ−π electron-donor−acceptor capability. The methoxy and the nitro substituted tetranilines show an interaction between the oxygen of the substitutent and the nitrogen of the oligomer through an hydrogen atom. These hydrogen bonds modify largely the structure of the oligomers. Particularly nitro groups show the strongest electrostatic attraction between hydrogen and oxygen. The cyano and the nitro groups (σ−π acceptor) induce an increasing of the ionization potential. Theoretical analysis of the orbital energies of molecules substituted with electron-acceptor groups shows a lowering of the LUMO energy values larger than those in the HOMOs cases. A decreasing of the energy of the first optical transition when the electron acceptor capability of the substituent increases is shown. Tetranilines substituted with nitro groups display a band around 380 nm in the calculated UV−vis spectrum. Thus, oligoanilines substituted with electron-acceptor groups (especially nitro groups) show the lowest energy gap and they are the most encouraging material for semiconducting applications that we have studied.

Effect of solvation and intermolecular interactions on the structure and optical properties of PANI oligomers

“…A number of communications tackle quantum chemical models of isolated PANI oligomers of different length and oxidation state 5–9. They discuss geometry, electronic structure, conductivity, and optical absorption of various oligomers ranging from dimers to dodecamers.…”

Alkyl Substituent Effects on the Conductivity of Polyaniline

“…The only other theoretical work known on substituent effects in polyanilines is that of Vaschetto and Retamal. [21] Their work on the oligoaniline tetramer using the semi-empirical PM3 method concluded that 2-and 3-substitution with methoxy, methyl, fluoro, cyano, and nitro groups leads to significant changes in both the geometric and electronic structure of oligoaniline systems. To some extent, our work agrees with their calculations though we use a somewhat different approach and a more advanced methodology.…”

Large first hyperpolarizabilities of substituted aniline oligomers

“…Recent theoretical works investigated the structural and electronic properties of substituted aniline oligomers [20,21,24,25]. Oligomers of aniline are considered electron donors, especially the emeraldine form [20].…”