Synthesis, thermal stability and photoresponsive behaviors of azobenzene-tethered polyhedral oligomeric silsesquioxanes
作者:Jinlan Zhou、Yongchen Zhao、Kaichao Yu、Xingping Zhou、Xiaolin Xie
DOI:10.1039/c1nj20577c
日期:——
A series of azobenzene-tethered polyhedral oligomeric silsesquioxane (POSS) derivatives, i.e.monoazobenzene-substituted POSS (MonoAzo-POSS), bisazobenzene-substituted POSS (BisAzo-POSS) and triazobenzene-substituted POSS (TriAzo-POSS), were synthesized through the amidation acidylation of aminopropylisobutyl POSS and benzoic acid derivatives (AzoMs) with one, two and three azobenzene groups (AzoM1, AzoM2 and AzoM3). Their structures were characterized by FT-IR, 1H NMR, 13C NMR and mass spectra, and their thermal stability and photoresponsive behaviors in DMF solutions were evaluated with TGA, XRD and UV-vis spectra, respectively. The results indicated that the thermal stability and photoisomerization of azobenzenes could be effectively controlled by their molecular structure. In MonoAzo-POSS, the large steric hindrance of POSS destroys the molecular ordering and limits the molecular packing, contributing to its poor thermal stability. And the low molecular ordering of MonoAzo-POSS offers an azo group with large free space, and its trans–cisphotoisomerization rate increases accordingly. But, in BisAzo-POSS and TriAzo-POSS, the incorporation of POSS units does not impact on the regularity of azobenzenes obviously, and the hindrance effect of nanosize POSS on the molecular motion plays a primary role in increasing their high thermal stability. Their photoisomerization rates decrease due to the steric hindrance of POSS and the unfolding structure of the azo moieties in BisAzo-POSS and TriAzo-POSS.
合成了一系列偶氮苯连接的多面体寡聚硅氧烷(POSS)衍生物,即单偶氮苯取代的POSS(MonoAzo-POSS)、双偶氮苯取代的POSS(BisAzo-POSS)和三偶氮苯取代的POSS(TriAzo-POSS),通过氨基丙基异丁基POSS与具有一个、两个和三个偶氮苯基团的苯甲酸衍生物(AzoMs)(AzoM1、AzoM2和AzoM3)进行酰胺化反应合成。这些衍生物的结构通过傅里叶变换红外光谱(FT-IR)、核磁共振氢谱(1H NMR)、碳谱(13C NMR)和质谱进行表征,其热稳定性和在DMF溶液中的光响应性质通过热重分析(TGA)、X射线衍射(XRD)和紫外-可见光谱(UV-vis)进行评估。结果表明,偶氮苯的热稳定性和光异构化可以通过其分子结构进行有效控制。在MonoAzo-POSS中,POSS的较大空间位阻破坏了分子有序性,限制了分子堆积,导致其热稳定性较差。而MonoAzo-POSS的低分子有序性为偶氮基团提供了较大的自由空间,其反式-顺式光异构化速率相应增加。然而,在BisAzo-POSS和TriAzo-POSS中,POSS单元的引入对偶氮苯的规律性影响不明显,POSS的纳米尺寸对分子运动的阻碍作用在提高其高热稳定性方面起主要作用。由于POSS的空间位阻和BisAzo-POSS及TriAzo-POSS中偶氮部分展开结构的影响,它们的光异构化速率降低。