The solid-state organization of ‘self-doped’ PPV oligomers

Abstract

Using a combination of multi-frequency EPR and NMR spectroscopy and quantum-chemical calculations at the level of Density Functional Theory (DFT), the organization of self-doped PPV oligomers in their solid state is investigated. The analysis of the different spectra shows that the electrochemical procedure used to self-dope these materials produces positive radicals (polarons) in an almost quantitative way, but still magnetically isolated polarons are observed. The difference between chemical and electrochemical oxidation of the oligomers is studied in detail. Furthermore, ageing of the electrochemically oxidized oligomers may be accompanied by a stacking of the oligomers.

Quantum chemical study of self-doping PPV oligomers: spin distribution of the radical forms

“…The maximum 1 H hyperfine coupling of oligomer 1 has been determined experimentally [16] and has a value of about 10.9 MHz. The absolute value of the calculated hyperfine coupling for hydrogen (D2) is about 11.6 MHz, in good agreement with the experimental value.…”

“…The EPR parameters were calculated with the ORCA package [27] using the B3LYP functional combined with the EPR-II basis set [28] for the carbon, hydrogen, and nitrogen atoms and the Ahlrichs-SVP basis set [29,30] for the oxygen and sulfur atoms. Identical basis sets were chosen as used in previous calculations [16]. For the fractional occupation Hirshfeld-I partitioning (FOHI), the atomic densities were calculated at every iteration using the BRABO program [31] with the B3LYP functional and 6-311?G* basis set.…”

“…2) would become available. Naturally, the introduction of nitrogen atoms in the carbon backbone of the oligomers leads to a rearrangement of the electron density, not only of the native, undoped material but also of the self-doped system, which would result in properties that differ considerably from those of, for instance, the original all-carbon material (1) [13,16].…”

Stacking Interactions of Poly Para-Phenylene Vinylene Oligomers with Graphene and Single-Walled Carbon Nanotubes: A Molecular Dynamics Approach

“…For example, intrinsically conducting polymers (ICPs) have become a significant aspect in the continuation of Moore’s law in the electronic industry, i.e., the number of transistors on integrated circuits roughly doubles biennially [ 1 ]. The reason for this is that the organic molecules can be easily processed, and uniquely adapted through doping in order to surpass the limitations of contemporary metal-oxide devices [ 2 ]. Electrical devices such as organic light-emitting diodes (OLEDs) [ 3 ], organic field-effect transistors (OFETs) [ 4 ], photovoltaic cells (PVCs) [ 5 ], light amplification by stimulated emission of radiation (LASER) devices [ 6 ] and sensors [ 7 ] have been manufactured from conducting polymers, and as such, significant resources have been invested in their research.…”

“…They require less effort to be functionalized and produced in large quantities and their synthesis can be well controlled to achieve high quality. This is compounded by the fact that oligomeric systems possess similar physical attributes to longer-chain systems such as the molecular arrangement, density, and conductivity [ 2 , 8 ], and thus, can be reliably used in characterization and substitution of larger systems.…”