Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Abstract

Changes in absorption spectra during doping of oligopyrroles were investigated with time-dependent density functional theory on optimized structures of neutral, singly, and doubly charged pyrrole oligomers with up to 24 rings. In the absence of counterions, defects are delocalized. Counterions induce localization. For dications two polarons on the same chain are preferred over a bipolaron. Intragap absorptions arise in charged species, no matter whether defects are localized or delocalized. Cations and dications give rise to two sub-band transitions. The cation peaks have lower energies than those of dications. The first excitations of cations have lower oscillator strengths than the second; for dications the second peak is weaker than the first. For very long oligomers, the second sub-band absorption vanishes and a third one appears at higher energy. The behavior of pyrrole oligomers is analogous to that of thiophene oligomers. Theoretical UV spectra for cations and dications of short oligomers (six to eight rings) match experimental spectra of polypyrrole at low and at high doping levels, respectively. The error in the theoretical calculations is about 0.4 eV, slightly larger than for thiophene oligomers at the same level of theory.

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

“…In particular, the formation of polarons gives rise to two doping-induced transitions whereas one transition of this type is characteristic for bipolarons. [73][74][75][76] Moreover polarons carry unpaired spins, thus their formation and recombination to bipolarons can be monitored by EPR spectroscopy. [77][78][79][80] Spectroscopic parameters of the investigated polymers in the neutral and p-doped states are collected in Table 9.…”

UV‐Printable and Flexible Humidity Sensors Based on Conducting/Insulating Semi‐Interpenetrated Polymer Networks

“…The peak at ≈470 nm represents high‐energy polaronic transitions that are characteristic of electron transitions from the valence band to the antibonding polaron; in other words, transitions inside the band gap. These characteristic peaks are in good agreement with what has been previously reported in literature . Therefore, while the pyrrole polymerizes to polypyrrole, absorptions in the UV region strongly occur, competing with the absorption of the photoinitiator which should promote the network formation consuming reactive functionalities.…”

“…These characteristic peaks are in good agreement with what has been previously reported in literature. [32,33] Therefore, while the pyrrole polymerizes to polypyrrole, absorptions in the UV region strongly occur, competing with the absorption of the photoinitiator which should promote the network formation consuming reactive functionalities. This is probably the cause of the lower conversions at higher pyrrole concentration but also the reason because it is not possible to further increase the pyrrole concentration over 15 wt%.…”

Electronic and optical properties of pyrrole and thiophene oligomers: A density functional theory study

“…For example, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) has been estimated for α,α'‐substituted oligothiophenes with up to six monomers, 6‐Py/6‐Th, using semi‐empirical Hartree–Fock (HF) or density functional theory (DFT) methods . The dynamic polarizability, excited states, geometry, and vibrational spectroscopy have been reported at the HF and DFT levels. More recently, the doping and dedoping processes of PPy, the structure of Py/Th oligomers, the charge distribution, the vibrational frequencies and the effects of perfluorination on Py/Th oligomers have been investigated using DFT calculations.…”