School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics , Georgia Institute of Technology , Atlanta , Georgia 30332-0400 , United States.
J Am Chem Soc. 2020 Jan 15;142(2):783-791. doi: 10.1021/jacs.9b08628. Epub 2020 Jan 2.
Here we report that a covalent organic framework (COF), which contains 2,5-di(imine)-substituted 1,4-dihydroxybenzene (diiminol) moieties, undergoes color changes in the presence of solvents or solvent vapor that are rapid, passive, reversible, and easily detectable by the naked eye. A new visible absorption band appears in the presence of polar solvents, especially water, suggesting reversible conversion to another species. This reversibility is attributed to the ability of the diiminol to rapidly tautomerize to an iminol/-ketoenamine and its inability to doubly tautomerize to a diketoenamine. Density functional theory (DFT) calculations suggest similar energies for the two tautomers in the presence of water, but the diiminol is much more stable in its absence. Time-dependent DFT calculations confirm that the iminol/-ketoenamine absorbs at longer wavelength than the diiminol and indicate that this absorption has significant charge-transfer character. A colorimetric humidity sensing device constructed from an oriented thin film of the COF responded quickly to water vapor and was stable for months. These results suggest that tautomerization-induced electronic structure changes can be exploited in COF platforms to give rapid, reversible sensing in systems that exhibit long-term stability.
在这里，我们报告了一种共价有机框架（COF），它含有 2,5-二（亚胺）取代的 1,4-二羟基苯（二亚胺醇）部分，在溶剂或溶剂蒸气存在下会发生快速、被动、可逆且可通过肉眼轻松检测到的颜色变化。在存在极性溶剂（特别是水）的情况下会出现新的可见吸收带，表明可可逆转化为另一种物质。这种可逆性归因于二亚胺醇迅速互变异构为亚胺/-酮亚胺的能力及其不能双互变异构为二酮亚胺的能力。密度泛函理论（DFT）计算表明，在存在水的情况下两种互变异构体的能量相似，但二亚胺醇在没有水的情况下更稳定。含时密度泛函理论（TD-DFT）计算证实，亚胺/-酮亚胺的吸收波长长于二亚胺醇，并表明这种吸收具有显著的电荷转移特征。由 COF 的取向薄膜构成的比色湿度感应装置对水蒸气的响应迅速，并且稳定数月。这些结果表明，互变异构诱导的电子结构变化可以在 COF 平台中得到利用，从而在具有长期稳定性的系统中实现快速、可逆的传感。
