Pang Juan, Shu Li, Li Ming, Hu Xiaohong
College of Material Science and Engineering, Jinling Institute of Technology Nanjing 211169 People's Republic of China
Department of Chemical and Materials Engineering, Hefei University Hefei 230601 People's Republic of China.
RSC Adv. 2020 Jun 17;10(39):23196-23202. doi: 10.1039/d0ra02468f. eCollection 2020 Jun 16.
In the present study, a colorimetric azobenzene-based probe (AZO 1) was reported that exhibits high selectivity toward Cu and undergoes a red to yellow colour change upon its detection. Density functional theory (DFT) calculations were carried out to investigate the mechanism of the probe discoloration. The differences in the binding energies of complexes of 2 : 1 and 1 : 1 stoichiometry indicated that a two-step complexation process takes place as the Cu content increases. However, the calculated absorption spectra suggested that a significant colour change would only be observed for the 1 : 1 AZO 1 : Cu complex. A HOMO-LUMO electronic transition was a key factor for the blue shift of the absorption bands of the probe. Further studies indicated that solvent molecules participate in the complexation and that the presence of the -methoxy group in AZO 1 led to formation of an octahedral complex because of the additional chelating site. A significant change in the conformation of AZO 1, namely the rotation of the ,-di(carboxymethyl)amino group around the N-C bond by approximately 90°, resulted in a larger HOMO-LUMO energy gap, and the corresponding alteration of the intramolecular charge transfer (ICT) from the ,-di(carboxymethyl)amino group to the phenyl ring led to the observed colour change.
在本研究中，报道了一种基于偶氮苯的比色探针（AZO 1），它对铜具有高选择性，并且在检测到铜时会发生从红色到黄色的颜色变化。进行了密度泛函理论（DFT）计算以研究探针变色的机制。2∶1和1∶1化学计量比的配合物结合能的差异表明，随着铜含量的增加，会发生两步络合过程。然而，计算得到的吸收光谱表明，只有1∶1的AZO 1∶Cu配合物会观察到显著的颜色变化。HOMO-LUMO电子跃迁是探针吸收带蓝移的关键因素。进一步的研究表明，溶剂分子参与了络合过程，并且由于额外的螯合位点，AZO 1中 -甲氧基的存在导致形成八面体配合物。AZO 1构象的显著变化，即，-二（羧甲基）氨基围绕N-C键旋转约90°，导致更大的HOMO-LUMO能隙，并且分子内电荷转移（ICT）从，-二（羧甲基）氨基到苯环的相应改变导致了观察到的颜色变化。
