Tuning of the H-bonding ability of imidazole N–H towards the colorimetric sensing of fluoride and cyanide ions as their sodium salts in water
作者:Ramalingam Manivannan、Angupillai Satheshkumar、Kuppanagounder P. Elango
DOI:10.1039/c3nj00371j
日期:——
Imidazole functionalized receptors, 2-R-1H-naphtho[2,3-d]imidazole-4,9-dione (2aâh), containing naphthoquinone as a chromogenic signalling unit have been synthesized from the reaction of 2,3-diaminonaphthoquinone and different aldehydes. These receptors showed a color change upon addition of fluoride and cyanide ions in DMSO with a bathochromic shift of the characteristic intramolecular charge transfer (ICT) transition band. No color change was observed upon addition of other anions such as Clâ, Brâ, Iâ, NO3â, AcOâ and H2PO4â. 1H NMR and electrochemical studies revealed that these receptors sense fluoride and cyanide ion via the formation of H-bond with the imidazole NâH moiety. Electronic and spectrofluorimetric studies indicated that the binding constants of these receptors with Fâ and CNâ ions were in the order of â¼106. The results of the spectral studies indicated that, by changing the R group in the receptor, the acidity of the imidazole NâH can be varied from δH 13.70 (for isopropyl) to 14.94 ppm (for thiophene). Theoretical calculations based on Density Functional Theory showed that the HOMOâLUMO energy gap for the ICT transition corroborate the results of the spectral studies. Receptor 2f (R = thiophene) was also able to detect fluoride and cyanide ions as their sodium salts in aqueous solution with a visual color change.
由 2,3-二氨基萘醌和不同的醛反应合成了咪唑官能化受体 2-R-1H-萘并[2,3-d]咪唑-4,9-二酮 (2aâh),其中含有作为发色信号单元的萘醌。在二甲基亚砜(DMSO)中加入氟离子和氰离子时,这些受体显示出颜色变化,分子内电荷转移(ICT)过渡带发生了浴色偏移。加入其他阴离子,如 Clâ、Brâ、Iâ、NO3â、AcOâ 和 H2PO4â 时,颜色没有变化。1H NMR 和电化学研究表明,这些受体通过与咪唑 NâH 分子形成 H 键来感知氟离子和氰离子。电子和光谱荧光研究表明,这些受体与氟离子和氰离子的结合常数为±106。光谱研究结果表明,通过改变受体中的 R 基团,咪唑 NâH 的酸度可以从 δH 13.70(异丙基)到 14.94 ppm(噻吩)变化。基于密度泛函理论的理论计算表明,ICT 过渡的 HOMOâLUMO 能隙证实了光谱研究的结果。受体 2f(R=噻吩)还能检测水溶液中的氟离子和氰离子钠盐,并呈现肉眼可见的颜色变化。