Department of Chemistry and Biochemistry and Integrative NanoScience Institute, Florida State University, 95 Chieftan Way, Tallahassee, Florida 32306, USA.
J Am Chem Soc. 2012 Aug 22;134(33):13679-91. doi: 10.1021/ja303173n. Epub 2012 Jun 28.
The recent emergence of anion-π interactions has added a new dimension to supramolecular chemistry of anions. Yet, after a decade since its inception, actual mechanisms of anion-π interactions remain highly debated. To elicit a complete and accurate understanding of how different anions interact with π-electron-deficient 1,4,5,8-naphthalenediimides (NDIs) under different conditions, we have extensively studied these interactions using powerful experimental techniques. Herein, we demonstrate that, depending on the electron-donating abilities (Lewis basicity) of anions and electron-accepting abilities (π-acidity) of NDIs, modes of anion-NDI interactions vary from extremely weak non-chromogenic anion-π interactions to chromogenic anion-induced charge-transfer (CT) and electron-transfer (ET) phenomena. In aprotic solvents, electron-donating abilities of anions generally follow their Lewis basicity order, whereas π-acidity of NDIs can be fine-tuned by installing different electron-rich and electron-deficient substituents. While strongly Lewis basic anions (OH(-) and F(-)) undergo thermal ET with most NDIs, generating NDI(•-) radical anions and NDI(2-) dianions in aprotic solvents, weaker Lewis bases (AcO(-), H(2)PO(4)(-), Cl(-), etc.) often require the photoexcitation of moderately π-acidic NDIs to generate the corresponding NDI(•-) radical anions via photoinduced ET (PET). Poorly Lewis basic I(-) does not participate in thermal ET or PET with most NDIs (except with strongly π-acidic core-substituted dicyano-NDI) but forms anion/NDI CT or anion-π complexes. We have looked for experimental evidence that could indicate alternative mechanisms, such as a Meisenheimer complex or CH···anion hydrogen-bond formation, but none was found to support these possibilities.
最近，阴离子-π 相互作用的出现为阴离子的超分子化学增添了新的维度。然而，自其诞生以来已经过去了十年，阴离子-π 相互作用的实际机制仍然存在很大争议。为了全面准确地了解不同阴离子在不同条件下如何与π-电子缺电子的 1,4,5,8-萘二酰亚胺（NDIs）相互作用，我们使用强大的实验技术广泛研究了这些相互作用。在这里，我们证明，取决于阴离子的供电子能力（路易斯碱性）和 NDIs 的吸电子能力（π-酸性），阴离子-NDI 相互作用的模式从非常弱的非生色阴离子-π 相互作用到生色阴离子诱导的电荷转移（CT）和电子转移（ET）现象不等。在非质子溶剂中，阴离子的供电子能力通常与其路易斯碱性顺序一致，而 NDIs 的π-酸性可以通过安装不同的富电子和缺电子取代基来进行微调。虽然强路易斯碱阴离子（OH(-) 和 F(-)）与大多数 NDIs 发生热 ET，在非质子溶剂中生成 NDI(•-)自由基阴离子和 NDI(2-)二阴离子，但较弱的路易斯碱（AcO(-)、H(2)PO(4)(-)、Cl(-)等）通常需要适度π-酸性 NDIs 的光激发通过光诱导 ET（PET）生成相应的 NDI(•-)自由基阴离子。路易斯碱性差的 I(-) 不参与大多数 NDIs 的热 ET 或 PET（除了与强π-酸性核取代二氰基-NDI 外），但形成阴离子/NDI CT 或阴离子-π 络合物。我们一直在寻找可以表明替代机制的实验证据，例如 Meisenheimer 络合物或 CH···阴离子氢键形成，但都没有发现支持这些可能性的证据。
