Poly(3-docosylthiophene) was found to have a two-step thermochromic process for samples that are rapidly cooled from the melt. The melt-quenched samples are a red-orange color that changes first to purple and then to yellow upon heating. In contrast, slowly cooled materials are purple and have a single thermochromic transition to yellow, typical of most poly(3-alkylthiophene)s. This phase behavior is found in both regioregular and regioirregular samples. The thermal behavior of the polymers was studied using differential scanning calorimetry and visible reflection spectroscopy. The DSC thermograms of slowly cooled samples show two endotherms upon heating and three exotherms upon cooling. In contrast, rapidly cooled samples exhibit three endotherms upon heating and three exotherms upon cooling. Reflection spectra show color changes that correlate with the DSC features. A model is proposed to explain the data that involves trapping of a high-temperature mesophase under the rapid cooling conditions.
A series of regioregular poly(3-alkylthiophene)s with substituent groups R = C22H45, C24H49, C26H53, and C28H57 were synthesized. All of the materials can form a mesophase by rapid quenching from the isotropic melt. The ease of mesophase formation depends upon the length of the alkyl group, with the longer side chains leading to mesophase formation at lower quenching rates. Variable temperature reflection and fluorescence spectroscopy of thin films and differential scanning calorimetry and variable temperature X-ray diffraction on powders were used to study the thermal behavior of the new polymers. All of the materials studied showed a two-step thermochromic transition from the mesophase, and endotherms in the thermograms could be assigned to melting of each phase. The data indicate that π−π stacking is an important contributor to the thermochromism observed in these compounds while the interaction between the alkyl side chains controls mesophase formation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations –citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.