Solid-solid transition of microcrystalline oligo(phenylene ethynylene)s: Impact of crystalline structure on optoelectronic properties

Abstract

Conjugated oligomers with distinct chain lengths, the trimers and pentamers of phenyleneethynylene units, have been investigated in this work with an aim to obtain ordered crystalline phases of the linear chain molecules. As such, we have observed a unique phase transition only in the pentamer. Unlike the case of the crystalline-liquid crystalline phase transition, the pentamer exhibited a unique solid-solid transition with uniaxial expansion in the condensed phase. Time-resolved microwave conductivity measurements suggested an interplay of the thermal activation of charge carriers, which enhanced the hopping probability, and uniaxial expansion reduced the electronic coupling in the π-stacking of adjacent molecules.