Doped Conductive Polymers: Modeling of Polythiophene with Explicitly Used Counterions

Abstract

The effect of counterions on the properties and structure of conducting polymers was studied by using a series of Cl3− doped polythiophenes (PTs) as a case example. Hybrid density functional theory (DFT) with periodic boundary conditions (PBC) at the B3LYP/6–31G(d) level has been used. This is the first theoretical study of infinitely long doped PT using DFT with counterions explicitly taken into account. The balance between charge carrier states was addressed by studying the singlet and triplet state unit cells of differently doped PTs. The relative isomer energies, density of states diagrams, bond length alternation, and charge distribution patterns were analyzed. Interestingly, the position of the counterion is flexible over the polymer chain and the electronic structure of the polymer and, consequently, optical properties are sensitive to the position of the counterion. A bipolaron electronic configuration is preferred at high dopant concentrations (one dopant per six or less thiophene rings) while a polaron pairs configuration is preferred at low dopant concentrations (one dopant per ten or more thiophene rings) which is in line with many experimental observations.

How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers

“…Restricted calculations (R-DFT) yield a much more limited intermolecular charge separation, resulting in a Mulliken net charge of 0.04 e on F4-TCNQ. As discussed by us 47 and other authors 22 , unrestricted calculations are more suitable for describing charge states and R-DFT was used only for control experiments (Fig. 4a).…”

“…The intrinsically more complex structure of the repeat unit of D-A copolymers, however, brings more difficulties to the microscopic description of doping in these systems. Studies aiming for a microscopic description of doping have appeared recently mainly focusing on homopolymers 12,[21][22][23][24][25] , leaving the challenge of describing the interaction between dopants and D-A alternating copolymers largely unaddressed. A detailed understanding of the mechanism of doping is needed in order to shed light on the very low amount of free charges per dopant (B4 charges donated every 100 dopants) observed in D-A copolymers 26 , and offer a solid understanding for future materials development.…”

Insulator to semimetallic transition in conducting polymers

“…Besides, this task requires approaches capable of calculating the electronic properties of systems consisting of hundreds * william.armando.munoz@liu.se † igor.zozoulenko@liu.se or thousands of atoms, which far exceeds the capabilities of standard quantum-mechanical packages. So far, the electronic properties of PEDOT and related conducting polymers have been studied on the basis of largely oversimplified models such as single polymeric chains [21][22][23][24] or infinite perfect periodic crystals [25][26][27]. None of these models are in a position to capture the morphology and the DOS of realistic PEDOT thin films.…”

Oligo‐ and Polyselenophenes: A Theoretical Study

“…The energies of the HOMO-SOMO transition are practically indistinguishable between oligothiophenes and oligoselenophenes, decrease rapidly with increasing chain length, and approach zero for long oligomers. Such transitions in oligothiophenes [49] and in doped polythiophenes [50] were studied previously in detail. In doped polythiophene with counterions explicitly included, this transition is in the order of 0.1-0.4 eV, depending on the position of the counterion.…”

“…In doped polythiophene with counterions explicitly included, this transition is in the order of 0.1-0.4 eV, depending on the position of the counterion. [50] The energy of the SOMO-LUMO transition in oligoselenophene cation radicals converges to a constant value of about 1.8 eV starting from the decamer, which is 0.2 eV lower than the corresponding transition in oligothiophene cation radicals.…”