pi-Conjugation and conformation in a semiconducting polymer: small angle x-ray scattering study

TL;DR

This study uses small angle X-ray scattering to investigate how pi-electron conjugation affects the conformation and assembly of a semiconducting polymer, revealing increased conjugation leads to longer chain persistence length and self-assembly tendencies.

Contribution

It provides new insights into how conjugation extent influences polymer chain rigidity and assembly behavior, using SAXS measurements on MEH-PPV.

Findings

Higher conjugation increases persistence length from 20 to 66 Å.

Fully conjugated chains show a second peak indicating self-assembly.

Solvent type affects chain conformation and rigidity.

Abstract

Small angle X-ray scattering (SAXS) in poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) solution has shown the important role of pi-electron conjugation in controlling the chain conformation and assembly. By increasing the extent of conjugation from 30 to 100 %, the persistence length (l_p) increases from 20 to 66 Angstrom. Moreover, a pronounced second peak in the pair distribution function has been observed in fully conjugated chain, at larger length scales. This feature indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. Xylene enhances the rigidity of PPV backbone to yield extended structures, while tetrahydrofuran solvates the side groups to form compact coils in which the l_p is much shorter.