Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation
Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation
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DOI：
10.1021/acs.jpcc.9b00005
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发表时间：
2019-03-14
影响因子：
3.7
通讯作者：
Mohammed, Omar F.
中科院分区：
文献类型：
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作者：
El-Zohry, Ahmed M.;Alturki, Abdullah;Mohammed, Omar F.
苯并噻二唑二苯甲酸（BTDB）衍生物是一种常见的金属有机骨架结构的有机连接剂，也是生物体系中的荧光探针。在这里，我们证明了BTDB的辐射和非辐射衰变通道可以相互作用，并通过浓度和氢键相互作用精确控制，直接证明实验和理论。这导致激发态结构的变化，显着抑制周围的苯并噻二唑部分的扭转运动，导致发射量子产率的巨大增加，从类似的1至70%。这些变化与两个平衡的存在有关，在二甲基甲酰胺（DMF）中形成二聚体和小的低聚物，形成常数分别为18 000 M-1和1.2 X 10（13）M-3。这些进化的物种，即，二聚物和低聚物通过存在于棒状BTDB分子远边的羧酸基团之间的氢键形成。如发射光谱分析所示，在DMF中通过键合单体形成这种小低聚物的估计重复数为8。以去质子化作为对照实验，这些相关物质可以很容易地与初始单体物质一起崩溃，证实了氢键形成在观察到的现象中的作用。理论研究和核磁共振实验不仅证实了二聚体的存在，而且证明了氢键在激发态动力学中的重要作用。这些新的发现提供了一个更好的理解，在广泛的化学和生物学应用中使用的有机连接器的物理行为。
Benzothiadiazole dibenzoic acid (BTDB) derivative is a well-known organic linker in various metal organic framework structures as well as a fluorescent probe in biological systems. Here, we demonstrate that the radiative and nonradiative decay channels of BTDB can be interplayed and precisely controlled through concentration and hydrogen-bond interactions as directly evidenced experimentally and theoretically. This leads to excited-state structural changes that significantly suppress the torsional motion around the benzothiadiazole moiety, leading to an enormous increase in the emission quantum yields from similar to 1 to 70%. These changes are associated with the existence of two equilibria, where dimers and small oligomers form in dimethylformamide (DMF), with high formation constants of 18 000 M-1 and 1.2 X 10(13) M-3, respectively. These evolving species, i.e., the dimers and oligomers, are formed via hydrogen bonds between carboxylic acid groups present at the far edge of the rodlike BTDB molecules. The estimated repeating number for this small-oligomer formation via bonded monomers is eight in DMF, as shown by emission spectra analysis. With deprotonation as a control experiment, these associated species can easily collapse with the initial monomer species, confirming the role of the hydrogen-bond formation in the observed phenomena. Theoretical studies and NMR experiments not only confirm the existence of the dimers, but also demonstrate the important role of the hydrogen bonds in the excited-state dynamics. These new findings provide a better understanding of the photophysical behaviors of organic linkers used in a wide range of chemical and biological applications.