Uniaxial Strain in Molecular Nanowires: A Case Study of β-phase Polyfluorenes

Abstract

The response of flexible organic semiconducting fluorene nanowires to structural manipulation and adsorption-induced uniaxial strain is investigated using first-principles methods. In agreement with experiments, the calculated shifts in transition energies of strained planar fluorenes do not lead to a molecular phase change but are modified according to whether deformations promote or suppress conjugation along the backbone. We identify two energetically identical modes for compressing the molecule, which cause shifts in opposite directions, depending on the impact of the deformation on the strength of conjugation. We also consider surface adsorption as a practical means for inducing strain. Although the polymer can be linearly extended through mismatch with the surface lattice, properties are likely to be dominated by local compressed regions.