Sun Yan, McFadden Molly E, Osler Skylar K, Barber Ross W, Robb Maxwell J
Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
Chem Sci. 2023 Sep 4;14(38):10494-10499. doi: 10.1039/d3sc03790h. eCollection 2023 Oct 4.
In contrast to common angular naphthopyrans that exhibit strong photochromic and mechanochromic behavior, constitutionally isomeric linear naphthopyrans are typically not photochromic, due to the putative instability of the completely dearomatized merocyanine product. The photochemistry of linear naphthopyrans is thus relatively understudied compared to angular naphthopyrans, while the mechanochromism of linear naphthopyrans remains completely unexplored. Here we demonstrate that the incorporation of a polarizing dialkylamine substituent enables photochromic and mechanochromic behavior from polymers containing a novel linear naphthopyran motif. In solution phase experiments, a Lewis acid trap was necessary to observe accumulation of the merocyanine product upon photochemical and ultrasound-induced mechanochemical activation. However, the same linear naphthopyran molecule incorporated as a crosslinker in polydimethylsiloxane elastomers renders the materials photochromic and mechanochromic without the addition of any trapping agent. This study provides insights into the photochromic and mechanochromic reactivity of linear naphthopyrans that have conventionally been considered functionally inert, adding a new class of naphthopyran molecular switches to the repertoire of stimuli-responsive polymers.
与表现出强烈光致变色和机械变色行为的常见角型萘并吡喃不同，由于推定的完全去芳香化部花青产物的不稳定性，结构异构的线性萘并吡喃通常不具有光致变色性。因此，与角型萘并吡喃相比，线性萘并吡喃的光化学研究相对较少，而线性萘并吡喃的机械变色现象仍完全未被探索。在此，我们证明，引入极化二烷基胺取代基可使含有新型线性萘并吡喃基序的聚合物具有光致变色和机械变色行为。在溶液相实验中，需要一个路易斯酸捕获剂来观察光化学和超声诱导的机械化学活化后部花青产物的积累。然而，作为交联剂掺入聚二甲基硅氧烷弹性体中的相同线性萘并吡喃分子，在不添加任何捕获剂的情况下使材料具有光致变色和机械变色性能。这项研究为传统上被认为功能惰性的线性萘并吡喃的光致变色和机械变色反应性提供了见解，为刺激响应聚合物的库中增加了一类新的萘并吡喃分子开关。
