Emissive Organic Exciplexes in Water
Emissive Organic Exciplexes in Water
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DOI：
10.1021/acs.joc.9b00718
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发表时间：
2019-06-21
影响因子：
3.6
通讯作者：
Farid, Samir
中科院分区：
文献类型：
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作者：
Dinnocenzo, Joseph P.;Mark, Analuz;Farid, Samir
与许多已知的激基复合物（电荷形成反应的产物）的例子不同，我们最近报道了阳离子激基复合物（电荷转移反应的产物）可以用N-甲基异喹啉鎓作为激发受体和烷基苯供体形成。我们现在已经合成了五种分子内类似物（通过三亚甲基链与烷基苯连接的异喹啉鎓），这些类似物被证明非常适合证明发射性激基复合物可以在水中由纯有机成分形成。结合吸收光谱、荧光测定法和时间相关单光子计数，鉴定了导致电子转移的三种构象异构体（反式构象异构体、左构象异构体和折叠构象异构体）。发现供体部分的疏水性增强了折叠构象异构体的形成，这直接导致激基复合物的形成。接地、电荷转移和局部激发态之间的电子耦合矩阵元素是根据辐射速率常数和平均发射频率之间的相关性确定的。激基复合物 (88-97%) 的电荷转移 (CT) 特征是根据电子耦合计算得出的。尽管在高极性溶剂中具有如此高的 CT 特性，但仍观察到激基复合物荧光量子产率高达 0.03，寿命高达 17 ns。
Unlike numerous known examples of exciplexes (products of charge formation reactions), we reported recently that cationic exciplexes (products of charge shift reactions) can be formed with N-methylisoquinolinium as an excited acceptor and alkyl benzene donors. We have now synthesized five intramolecular analogues (isoquinolinium linked by a trimethylene tether to alkyl benzenes) that proved to be well suited to demonstrating that emissive exciplexes can be formed in water from purely organic components. Three conformers (anti, gauche, and folded) leading to electron transfer were identified using a combination of absorption spectroscopy, fluorometry, and time-correlated single photon counting. The hydrophobicity of the donor moiety was found to enhance the formation of the folded conformer, which leads directly to exciplex formation. Electronic coupling matrix elements between ground, charge transfer, and locally excited states were determined from correlations between radiative rate constants and average emission frequencies. The charge transfer (CT) character of the exciplexes (88-97%) was calculated from the electronic coupling. In spite of such a high CT character in a highly polar solvent, exciplex fluorescence quantum yields up to 0.03 and lifetimes up to 17 ns were observed.