Molecular Orientation and Field-effect Transistors of a Rigid Rod Conjugated Polymer Thin Films

Molecular orientation in thin films of a rigid rod conjugated polymer, a derivative of poly(para-phenylene ethynylene)s with linear side chains and thioacetyl end groups, was investigated by reflection−absorption infrared spectroscopy and X-ray diffraction technique. The results indicated that TA-PPE molecules tended to align with their backbone planes perpendicular to substrates, that is, with an “edge-on” molecular orientation in the films. Such molecular orientation is favorable for the efficient carrier transport in two-dimensional direction in the polymer films (i.e., via both the intrachain and interchain), so that high performance organic field-effect transistors were fabricated with hole mobility at around ∼4.3 × 10⁻³ cm²/Vs.