Boundaries of Anion/Naphthalenediimide Interactions: From Anion-π Interactions to Anion-Induced Charge-Transfer and Electron-Transfer Phenomena
Boundaries of Anion/Naphthalenediimide Interactions: From Anion-π Interactions to Anion-Induced Charge-Transfer and Electron-Transfer Phenomena
复制标题
DOI：
10.1021/ja303173n
复制
发表时间：
2012-08-22
影响因子：
15
通讯作者：
Saha, Sourav
中科院分区：
文献类型：
--
作者：
Guha, Samit;Goodson, Flynt S.;Saha, Sourav
阴离子 - π相互作用的近期出现为阴离子超分子化学增添了新的维度。然而，自其诞生十年以来，阴离子 - π相互作用的实际机制仍然备受争议。为了全面且准确地理解不同阴离子在不同条件下如何与缺π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对这些相互作用进行了广泛研究。在此，我们证明，根据阴离子的给电子能力（路易斯碱度）和NDIs的受电子能力（π酸性），阴离子 - NDI相互作用的模式从极弱的非生色阴离子 - 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，阴离子的给电子能力通常遵循其路易斯碱度顺序，而NDIs的π酸性可通过引入不同的富电子和缺电子取代基进行精细调节。强路易斯碱阴离子（OH⁻和F⁻）与大多数NDIs发生热电子转移，在非质子溶剂中生成NDI⁻·自由基阴离子和NDI²⁻二价阴离子，较弱的路易斯碱（AcO⁻、H₂PO₄⁻、Cl⁻等）通常需要中等π酸性的NDIs进行光激发，通过光诱导电子转移（PET）生成相应的NDI⁻·自由基阴离子。弱路易斯碱I⁻不与大多数NDIs参与热电子转移或光诱导电子转移（除了与强π酸性的核心取代二氰基 - NDI），而是形成阴离子/NDI电荷转移或阴离子 - π复合物。我们寻找了可能表明替代机制的实验证据，例如迈森海默复合物或C - H···阴离子氢键的形成，但没有发现支持这些可能性的证据。
The recent emergence of anion-pi interactions has added a new dimension to supramolecular chemistry of anions. Yet, after a decade since its inception, actual mechanisms of anion-pi interactions remain highly debated. To elicit a complete and accurate understanding of how different anions interact with pi-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 (pi-acidity) of NDIs, modes of anion-NDI interactions vary from extremely weak non-chromogenic anion-pi 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 pi-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 center dot- radical anions and NDI2- dianions in aprotic solvents, weaker Lewis bases (AcO-, H2PO4-, Cl-, etc) often require the photoexcitation of moderately pi-acidic NDIs to generate the corresponding NDI center dot- radical anions via photoinduced ET (PET). Poorly Lewis basic I- does not participate in thermal ET or PET with most NDIs (except with strongly pi-acidic core substituted dicyano-NDI) but forms anion/NDI CT or anion-pi complexes. We have looked for experimental evidence that could indicate alternative mechanisms, such as a Meisenheimer complex or CH center dot center dot center dot anion hydrogen bond formation, but none was found to support these possibilities.