ROD-TO-COIL TRANSITION IN ALKOXY-SUBSTITUTED POLYTHIOPHENES

Temperature-dependent UV-visible absorption measurements have revealed reversible thermochromic effects (a 0.95-eV shift in the maximum of absorption) in amorphous poly[3-(octyloxy)-4-methylthiophene] (POMT). The presence of a solid-state "phase" transition was also confirmed by infrared and calorimetric analyses. All these experimental results are consistent with a conformational transition of the conjugated polymer chain from a coplanar (rod) structure at room temperature to a nonplanar (coil) form at 150-degrees-C. According to theoretical calculations, the less conjugated form of POMT can be related to the presence of a torsion angle of +/- 45-degrees between each consecutive repeat unit.