Crystalline Nanochannels with Pendant Azobenzene Groups: Steric or Polar Effects on Gas Adsorption and Diffusion?
Crystalline Nanochannels with Pendant Azobenzene Groups: Steric or Polar Effects on Gas Adsorption and Diffusion?
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DOI：
10.1021/jacs.7b02979
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发表时间：
2017-07-05
影响因子：
15
通讯作者：
Aida, Takuzo
中科院分区：
文献类型：
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作者：
Huang, Hubiao;Sato, Hiroshi;Aida, Takuzo
一种含偶氮苯的锆基金属有机骨架（（MOF）-M-Azo），在用365 +/- 10 nm的紫外（UV）光照射时，在30 min内，在光稳定状态下，其偶氮苯侧基经历反式至顺式异构化，得到顺式异构体含量为21%（（MOF21%）-M-Azo），并经历反向异构化为（MOF1%）-M-Azo。在可见光（420-480 nm）照射或加热时偶氮。随着顺式异构体含量的增加，CO2在（MOF）-M-Azo纳米通道中的扩散速率和吸附量均显著降低。当使用赤藓红B（一种极性探测客体）时，它在EB的（MOF 20%）-M-Azo超集暴露于可见光时显示出红移，表明随着反式异构体含量变得更高，（MOF）-M-Azo的内部环境变得极性更小。与此形成鲜明对比的是，（MOF15%）-M-Azo和（MOF1%）-M-Azo对具有与CO2相似动力学直径但没有四极矩和较小极化率的Ar的吸附曲线几乎彼此相同。因此，很可能CO2在结晶纳米通道中经历极性效应而不是空间效应的主导效应。
An azobenzene-containing, zirconium based metal organic framework ((MOF)-M-Azo), upon irradiation with ultraviolet (UV) light at 365 +/- 10 nm, underwent trans-to-cis isomerization of its azobenzene pendants to furnish the cis-isomer content of 21% ((MOF21%)-M-Azo) in 30 min at the photostationary state and underwent backward isomerization into (MOF1%)-M-Azo upon either irradiation with visible light (420-480 nm) or heating. When the cis-isomer content increased, the diffusion rate and amount of CO2 adsorbed into the nanochannels of (MOF)-M-Azo decreased considerably. When erythrosine B, a polarity-probing guest, was used, it showed a red shift upon exposure of (MOF20%)-M-Azo superset of EB to visible light, indicating that the interior environment of (MOF)-M-Azo turns less polar as the trans-isomer content becomes higher. In sharp contrast, the adsorption profiles of (MOF15%)-M-Azo and (MOF1%)-M-Azo for Ar having an analogous kinetic diameter to CO2 but no quadrupole moment and a smaller polarizability were virtually identical to one another. Therefore, it is likely that CO2 experiences a dominant effect of a polar effect rather than a steric effect in the crystalline nanochannels.