功能化的光致变色螺噁嗪寡聚物:使用 NMR 光谱和 DFT 研究核-寡聚物相互作用和光致变色菁互变。
Photochromic spirooxazines functionalized with oligomers: investigation of core-oligomer interactions and photomerocyanine isomer interconversion using NMR spectroscopy and DFT.
机构信息
Centre for Marine Bio-Innovation, The University of New South Wales, Sydney, NSW 2052, Australia.
出版信息
J Org Chem. 2010 May 7;75(9):2851-60. doi: 10.1021/jo100081g.
Photochromic spirooxazines functionalized with poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) oligomers were monitored using NMR spectroscopy at temperatures between 193 and 233 K before and after in situ exposure to UV irradiation. NOESY and ROESY experiments reveal the TTC (trans-s-trans-cis) isomer to be the dominant merocyanine isomer formed on photolysis, with some CTC (cis-s-trans-cis) isomer also present. Significant ROE cross peaks were observed between the "bulk" of the oligomeric units and protons across the entire photochromic core of the molecule, the intensity of these cross peaks suggesting that the interaction of the oligomer side chain and core of the molecule is significantly enhanced by the permanent attachment, especially with the PDMS side chain. The 2D NMR spectra indicate that there is exchange between the TTC and CTC isomers even at 193 K. This isomerization of the parent spirooxazine compounds, lacking the oligomeric side chains, was found to be acid-catalyzed, and DFT calculations support the strong possibility that it is the protonated merocyanine form that undergoes the facile isomerization process. Interconversion of the different merocyanine isomers is suggested to be fast on the NMR time scale under many experimental conditions, precluding the observation of different isomers using NMR spectroscopy at room temperature.
用 NMR 光谱法在 193 至 233 K 温度范围内监测了用聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)低聚物官能化的光致变色螺噁嗪,在现场暴露于紫外光照射前后进行了监测。NOESY 和 ROESY 实验表明,TTC(trans-s-trans-cis)异构体是光解时形成的主要的次甲基蓝异构体,也存在一些 CTC(cis-s-trans-cis)异构体。在整个分子的光致变色核心中,观察到“大块”低聚物单元与质子之间存在显著的 ROE 交叉峰,这些交叉峰的强度表明,低聚物侧链与分子核心的相互作用通过永久附着显著增强,特别是与 PDMS 侧链。2D NMR 谱表明,即使在 193 K 下,TTC 和 CTC 异构体之间也存在交换。发现没有低聚物侧链的母体螺噁嗪化合物的这种异构化是酸催化的,并且 DFT 计算支持这样一种强烈的可能性,即质子化的次甲基蓝形式经历了易于异构化的过程。在许多实验条件下,不同的次甲基蓝异构体之间的互变异构被认为在 NMR 时间尺度上很快,从而排除了在室温下使用 NMR 光谱法观察不同异构体的可能性。