Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.
J Chem Phys. 2018 Nov 28;149(20):204503. doi: 10.1063/1.5052003.
Improvements to the photostability of organic glasses for use in electronic applications have generally relied on the modification of the chemical structure. We show here that the photostability of a guest molecule can also be significantly improved-without chemical modification-by using physical vapor deposition to pack molecules more densely. Photoisomerization of the substituted azobenzene, 4,4'-diphenyl azobenzene, was studied in a vapor-deposited glass matrix of celecoxib. We directly measure photoisomerization of - to -states via Ultraviolet-visible (UV-Vis) spectroscopy and show that the rate of photoisomerization depends upon the substrate temperature used during co-deposition of the glass. Photostability correlates reasonably with the density of the glass, where the optimum glass is about tenfold more photostable than the liquid-cooled glass. Molecular simulations, which mimic photoisomerization, also demonstrate that photoreaction of a guest molecule can be suppressed in vapor-deposited glasses. From the simulations, we estimate that the region that is disrupted by a single photoisomerization event encompasses approximately 5 molecules.
为提高用于电子应用的有机玻璃的光稳定性，通常依赖于化学结构的改性。我们在此表明，通过使用物理气相沉积使分子更紧密地堆积，也可以在不进行化学修饰的情况下显著提高客体分子的光稳定性。在塞来昔布的气相沉积玻璃基质中研究了取代偶氮苯，4,4'-二苯基偶氮苯的光异构化。我们通过紫外-可见（UV-Vis）光谱直接测量了 - 到 - 态的光异构化，并表明光异构化的速率取决于共沉积过程中使用的基底温度。光稳定性与玻璃的密度合理相关，其中最佳玻璃的光稳定性比液冷玻璃高约十倍。模拟光异构化的分子模拟也表明，气相沉积玻璃可以抑制客体分子的光反应。从模拟中，我们估计单个光异构化事件所破坏的区域大约包含 5 个分子。
