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 o f the octyl side groups: POT is head-to-rail attached with essentially plan ar main chains, whereas PDOT2 is head-to-head/tail-to-tail attached, with t wisted main chains. The present work shows that POT possesses a much more a nisotropic compressibility than PDOT2, POT being particularly compressible along the direction of the side chains, which due to the alkyl bond flexibi lity is the most deformable part of the materials. The observed volume comp ressibility of POT is discussed in relation to reported pressure and temper ature shifts of the absorption spectrum.