Qiu Wenlian, Gurr Paul A, Qiao Greg G
Department of Chemical Engineering , The University of Melbourne , Parkville , Victoria 3010 , Australia.
ACS Appl Mater Interfaces. 2019 Aug 14;11(32):29268-29275. doi: 10.1021/acsami.9b09023. Epub 2019 Aug 5.
Spiropyran is an important mechanophore, which has rarely been incorporated as a cross-linker in polar polymer matrices, limiting its applications in innovative mechanochromic devices. Here, three spiropyrans with two- or three-attachment positions were synthesized and covalently bonded in polar poly(hydroxyethyl acrylate) (PHEA), to achieve color-switchable materials, triggered by light and when swollen in water. The negative photochromism in the dark and mechanical activation by swelling in water were investigated. Measurements of negative photochromism were conducted in solution and cross-linked PHEA bulk polymers, with both showing color reversibility when stored in the dark or on exposure to visible light. The force of swelling in water was sufficient to induce the ring-opening reaction of spiropyran. It was found that tri-substituted spiropyran (SP3) was less influenced by the polar matrix but showed the fastest color activation during swelling. SP3 also showed accelerated ring opening to the colored state during the swelling process. Bleaching rates and color switchability were investigated under swollen and dehydrated conditions. The effect of cross-link density on the swelling activation was explored to better understand the interaction between the mechanophore and the polar environment. The results demonstrated that influences from both the polar environment and the mechanochromic nature of spiropyran had an impact on the absorption intensity, rate of change, and the decoloration rate of the materials. This study provides the opportunity to manipulate the properties of spiropyrans to afford materials with a range of color-switching properties under different stimuli.
螺吡喃是一种重要的机械响应基团，在极性聚合物基体中很少被用作交联剂，这限制了其在创新型机械变色器件中的应用。在此，合成了三种具有两个或三个连接位置的螺吡喃，并将其共价键合到极性聚（丙烯酸羟乙酯）（PHEA）中，以实现由光触发以及在水中溶胀时颜色可切换的材料。研究了黑暗中的负光致变色以及在水中溶胀引起的机械活化。在溶液和交联的PHEA本体聚合物中进行了负光致变色测量，两者在黑暗中储存或暴露于可见光时均表现出颜色可逆性。在水中溶胀的力足以诱导螺吡喃的开环反应。发现三取代螺吡喃（SP3）受极性基体的影响较小，但在溶胀过程中颜色活化最快。SP3在溶胀过程中还表现出向有色状态的加速开环。研究了溶胀和脱水条件下的漂白速率和颜色可切换性。探索了交联密度对溶胀活化的影响，以更好地理解机械响应基团与极性环境之间的相互作用。结果表明，极性环境和螺吡喃的机械变色性质的影响均对材料的吸收强度、变化速率和褪色速率产生影响。本研究提供了调控螺吡喃性质的机会，以获得在不同刺激下具有一系列颜色切换特性的材料。
