Solid-state optical and structural modifications induced by temperature in a chiral poly-3-alkylthiophene

Polyalkylthiophenes bearing enantiomerically pure side chains are noncentrosymmetric materials that can be used in polarized photo- and electroluminescence areas and enantio-selective sensing. In this work we present the characterization of a polyalkylthiophene with a chiral center very close to the conjugated backbone: poly-3-(S)-2-methylbutylthiophene (PMBT). Differential scanning calorimetry and X-ray diffraction measurements have been performed to characterize the thermal transitions and the structural organization of this polymer. Thin films of PMBT exhibit interesting thermochromism phenomena that affect absorption, emission, and circular dichroism properties. The influences of both the film processing and the thermal treatment on the conjugated polymeric chains have been studied by UV-visible, FTIR, and Raman spectroscopies. Thermochromism has been monitored by in situ electronic absorption, circular dichroism, and photoluminescence experiments. Electroluminescence properties and the electrical characterization of a single-layer lightemitting diode are also presented. The optical and structural changes induced by the temperature are discussed in terms of the peculiar three-dimensional order found for this polymer with respect to other poly-3-alkylthiophenes.