Polymorphs and Colors of Polydiacetylenes: A First Principles Study

Polydiacetylenes (PDAs) are exceptional polymeric materials with π-conjugated backbones. Several of them can undergo chromogenic transitions under a wide range of external stimuli. Herein we investigate the electronic structure and the resulting properties of model and experimental PDAs, by means of first principles condensed matter calculations. It is shown that torsional isomers with a twist of the lateral groups can be formed at small energetic costs. We also show the relationship that exists between these twists and the observed changes in the electronic and physical properties. In particular, the calculated changes in the absorption, Raman and NMR spectra agree with the color and property changes as observed experimentally. Therefore, these isomers are excellent models for the structures involved in the chromogenic transitions.

聚二乙炔（Polydiacetylenes, PDAs）是一类具备π共轭主链的优异聚合物材料。其中多种可在多种外部刺激下发生发色转变。本文通过第一性原理凝聚态计算方法，对模型与实验体系中的PDAs的电子结构及其衍生性质展开研究。研究表明，侧基发生扭转的扭转异构体仅需极低的能量代价即可形成。此外，本文还揭示了此类侧基扭转与电子及物理性质变化之间的内在关联。尤为关键的是，计算得到的吸收光谱、拉曼光谱与核磁共振（NMR）谱的变化，与实验中观测到的颜色与性质变化高度吻合。因此，此类扭转异构体可作为发色转变过程中涉及的结构的优质模型体系。