Molecular photoswitches have been incorporated into polymer backbones to control the macromolecular conformations by structural changes of the main-chain photoswitches. However, previous photoswitches installed in the main chains are thermolabile, which precludes deep understanding, precise regulation, and practical applications of the macromolecular conformational changes. Herein, we focus on sterically hindered stiff stilbene (HSS), an emerging photoswitch offering large structural changes in isomerization between the thermally bistable E and Z isomers, and disclose the chemistry of main-chain HSS photoswitches in solution, in bulk, and at thin film surfaces. We synthesize and investigate three types of linear polymers with different chemical linkages between HSS repeating units, polyurethane, polyester, and polyene. The polymer conformations in solution, i.e., hydrodynamic volume, are reversibly photocontrollable in a precise manner by the E/Z ratio. Further, the nanoscopic conformational transformations are amplified to macroscopic photoswitching of the solution transmittance and the surface wettability synergistically with changes between interchain and intrachain hydrogen bonding in the polyurethanes. Additionally, the Z-to-E photoisomerization in the glassy state yields above 70%, which is comparable to that in solution and extraordinarily high despite the restricted molecular mobility. The findings in this study will pave the way for practical and unconventional applications of smart polymer systems based on photoswitches.

中文翻译：

---

主链 stiff-stilbene 在溶液、块体和表面的光开关


分子光开关已被掺入聚合物骨架中，以通过主链光开关的结构变化来控制大分子构象。然而，以前安装在主链中的光开关不耐热，这排除了对大分子构象变化的深入理解、精确调节和实际应用。在本文中，我们专注于空间受阻硬二苯乙烯 （HSS），这是一种新兴的光开关，在热双稳态 E 和 Z 异构体之间提供较大的异构化结构变化，并揭示了主链 HSS 光开关在溶液、块体和薄膜表面的化学性质。我们合成并研究了三种类型的线性聚合物，它们在 HSS 重复单元、聚氨酯、聚酯和聚乙烯之间具有不同的化学键。溶液中的聚合物构象，即流体动力学体积，可以通过 E/Z 比以精确的方式进行可逆的光控。此外，纳米级构象转变被放大为溶液透射率和表面润湿性的宏观光开关，与聚氨酯中链间和链内氢键的变化协同作用。此外，玻璃态下的 Z-to-E 光异构化率超过 70%，这与溶液中的产量相当，并且在分子迁移率有限的情况下非常高。本研究的结果将为基于光开关的智能聚合物系统的实际和非常规应用铺平道路。