Poly(octyl-thiophene) polymorphs under high pressure: Synchrotron X-Rays studies and the relation with spectral behaviour

The two materials studied differ from each other by the attachment scheme of the octyl side groups: POTis head-to-tail attached with essentially planar main chains, whereas PDOT2 is head-to-head/tail-to-tail attached, with twisted main chains. The present work shows that POT possesses a much more anisotropic compressibility than PDOT2, POT being particularly compressible along the direction of the side chains, which due to the alkyl bond flexibility is the most deformable part of the materials. The observed volume compressibility of POT is discussed in relation to reported pressure and temperature shifts of the absorption spectrum.