Calculations of Band Gaps in Polyaniline from Theoretical Studies of Oligomers

Abstract

Geometries and band gaps of polyaniline oligomers up to decamer have been systematically calculated and analyzed using various computational techniques such as molecular mechanics, semiempirical, and ab initio methods. On the basis of fully optimized geometries of neutral and charged forms of polyaniline oligomers, excitation energies are calculated at the semiempirical ZINDO (INDO/S) level and extrapolated to the band gap value of the infinite chain. Band gaps are also approximated by extrapolating the HOMO/LUMO difference calculated at the density functional level (B3LYP/6-31G*). The ZINDO//AM1 band gaps in the reduced and oxidized form of polyaniline (4.3 and 2.7 eV) are in good agreement with experimental values (3.8 ( 2 and 1.8 ( 3 eV, respectively). The doped form of polyaniline (two positive charges per four aniline units) has been computed with a spin-unrestricted method (UAM1) and the band gap approximated from an extrapolation of the tetramer and octamer. The calculated band gap of 1.3 eV (UZINDO//UAM1) is in good agreement with experiment (1.5 eV). The influence of ring torsional angle and interchain interaction on the band gap of the polyaniline system are also discussed.

Large first hyperpolarizabilities of substituted aniline oligomers

“…Kwon and McKee [17] performed a systematic analysis of the nonfunctionalized aniline oligomer geometries for several chain sizes, except for the emeraldine form, using molecular mechanics (MMFF), semiempirical (AM1), Density Functional Theory (DFT), and ab initio methods. It was demonstrated that the DFT method is more reliable and is in agreement with experimental parameters.…”

“…The polyaniline polymer pre-sents a large third-order susceptibility [10 -12]. Oligomers of aniline have been used as model systems to simulate some polyaniline properties [13][14][15][16][17]. Furthermore, at the AM1/TDHF level of calculation it was observed that model trimers simulate the observed experimental trends for the second hyperpolarizability (␥) of polyaniline [18].…”

Aromaticity of Giant Polycyclic Aromatic Hydrocarbons with Hollow Sites: Super Ring Currents in Super‐Rings

“…At the B3LYP level the single-double bond equalization is much more pronounced than at the HF and CNDO levels of theory. It is indeed well-known that theoretical approaches that lack electron correlation tend to systematically overestimate the extent of bond-length alternations in extended p-conjugated chains [71,[82][83][84][85] to prevent a closure of the HOMO-LUMO gap and near-energy degeneracies therefore. Table 4, along with those found for [18]- [66]annulenes.…”

Высокая Подвижность Носителей Заряда В Молекулярных Каналах Полианилина В Нанозазорах Между Углеродными Нанотрубками

“…Легирование эмеральдинового основания приводит к переходу ПАНИ в эмеральдиновую соль, что увеличи-вает его проводимость на 9 порядков. Уровень Ферми УНТ (энергия ∼ 5 эВ) расположен в запрещенной зоне полимера и очень близок к уровню его высшей заня-той молекулярной орбитали (ВЗМО) [11], что должно способствовать высокой инжекции заряда (дырок) из электродов в молекулу. При создании раствора для оса-ждения полианилина в качестве растворителя был вы-бран 1-метил-2-пирролидон (НМП/NMP).…”