Thermochromism and Structural Change in Polydiacetylenes Including Carboxy and 4‑Carboxyphenyl Groups as the Intermolecular Hydrogen Bond Linkages in the Side Chain

We investigated the thermochromic behavior of polydiacetylenes including the carboxy and 4-carboxyphenyl groups as the side-chain substituents adjacent to the conjugated main chain, and then, the thermal stability and the thermochromism reversibility of the polymers were related to changes in the polymer conformations monitored by IR and Raman spectroscopies and powder X-ray diffractions. The polydiacetylenes with no or a phenylene spacer between the main chain and the carboxylic acid moiety were revealed to exhibit a thermal resistance for maintaining reversible thermochromism in a high temperature range, rather than polydiacetylenes with a conventional structure with a flexible alkylene spacer. The molecular stacking structures of the diacetylenes and the corresponding polymers in the crystals were discussed based on the results of an X-ray single-crystal structure analysis as well as the powder X-ray diffraction measurements.本研究针对共轭主链邻侧带有羧基与4-羧基苯基作为侧链取代基的聚二乙炔类聚合物，考察其热致变色行为；随后通过红外（IR）光谱、拉曼（Raman）光谱与粉末X射线衍射表征聚合物构象变化，关联该类聚合物的热稳定性与热致变色可逆性。研究发现，相较于主链与羧酸官能团间带有柔性亚烷基间隔基的传统结构聚二乙炔，主链与羧酸官能团间无间隔基或带有亚苯基间隔基的聚二乙炔，可在高温区间维持可逆热致变色的耐热性能。本研究还结合单晶X射线结构分析与粉末X射线衍射测试结果，探讨了二乙炔单体及其对应聚合物在晶体中的分子堆积结构。