Two laterally non-symmetric aza-oxa cryptands have been derivatized with the electron-withdrawing fluorophore, 7-nitrobenz-2-oxa-1,3-diazole to obtain the corresponding mono-, bis- and tris-products. In each case, no appreciable emission is observed when the fluorophore is excited due to an efficient photoinduced intramolecular electron transfer (PET) from the lone pair on nitrogen present in the bridges. In the presence of a number of transition and heavy metal ions, their emission characteristics change. The electron-withdrawing ability of the fluorophore drastically alters the binding ability of the cryptand such that Hg(II) affords largest enhancement of fluorescence. In contrast, mono-, bis- and tris-anthryl (electron-donating) derivatives of these cryptands do not exhibit any selectivity towards Hg(II) and affords low fluorescence enhancement. Also, the difference in cavity dimension of the o-cryptand and m-cryptand plays a crucial role in terms of selectivity.
两种侧向非对称的氮氧杂环类
穴醚已经通过电子吸引性的荧光团7-
硝基苯-2-氧杂-1,3-二氮杂进行衍生化,得到了相应的单、双和三取代产物。在这些情况下,由于桥中氮原子上孤对电子引起的有效的光诱导分子内电子转移(PET),当荧光团被激发时,没有观察到明显的荧光发射。在存在多种过渡
金属和重
金属离子的情况下,它们的荧光特性发生变化。荧光团的电子吸引能力极大地改变了
穴醚的结合能力,使得Hg(II)离子提供了最大的荧光增强。相比之下,这些
穴醚的单、双和三芳基(电子供体)衍
生物对Hg(II)没有显示出任何选择性,并且提供的荧光增强效果较低。此外,氮氧杂环
穴醚的o型和m型在腔体尺寸上的差异对于选择性也起着至关重要的作用。