STUDY OF DUAL FLUORESCENCE OF FLUORINATED BENZOAZOLES AND THEIR APPLICATION AS CHEMOSENSORS

合成了含咪唑基团1的2-（2-羟基氟苯基）苯并恶唑，并将其双重荧光应用于金属阳离子的多重化学传感器中，在氯仿-乙腈溶液中，加入Al^3+>、Zn^2+>或Mg^2+>可使其产生绿色发射和微弱的蓝色发射，这两种发射的增强比例取决于捕获的金属阳离子.该绿色发射归因于金属阳离子与咪唑氮原子的连接，并且所产生的氮原子的正性被诱导地传递到羟基，以恢复其氢键能力，从而导致激发态分子内质子转移（ESIPT）过程。发现2-（2-氨基氟苯基）苯并恶唑衍生物，特别是2-（2-五氟苯甲酰氨基-3，4，5，6-四氟苯基）苯并恶唑具有绿色发射。绿色发射在非极性溶剂中增强，导致相当大的斯托克斯位移。此外，取代苯并恶唑环系统，合成了相应的咪唑并吡啶环系统构成的荧光团，并揭示了它们的识别能力。2-（3，4，5，6-四氟-2-羟基苯基）咪唑并吡啶（2）被证明具有作为金属阳离子的荧光化学传感器的高潜力，其可以发出对应于每个捕获的金属阳离子的不同波长发射的信号。在乙腈溶液中，当2与Zn^<2+>离子反应时，在430 nm附近产生蓝光发射;当2与Al^<3+>和Hg^<2+>离子反应时，在370 nm附近产生天蓝色发射。这种能力归因于络合物，其中金属阳离子上连接的羟基和配位的水分子通过氢键连接到2的1-氮原子和2-氟原子。

2-(2-Hydroxyfluorophenyl)benzoxazole having imidazole moiety 1 is synthesized and its dual fluorescence is applied to a multiple chemosensor for metal cations ; addition of Al^<3+>, Zn^<2+>, or Mg^<2+> causes the green emission together with slight blue emission in chloroform-acetonitrile, the enhancement ratio of both emissions being dependent on the captured metal cations. The green emission is ascribed to the ligation of the metal cation on the imidazole nitrogen atom, and the resulting positive character of nitrogen atom is inductively communicated to the hydroxyl group, to recover its hydrogen bonding ability leading to the excited state intramolecular proton transfer (ESIPT) process. The green emission is found with 2-(2-aminofluorophenyl)benzoxazole derivatives, particularly with 2-(2-pentafluorobenzamido-3,4,5,6- tetrafluorophenyl)benzoxazole. The green emission is enhanced in nonpolar solvents, resulting in the considerably large Stokes shift. Moreover, in place of the benzoxazole ring system, the corresponding fluorophores constituted by imidazopyridine ring system are synthesized and their recognition ability is disclosed. 2-(3,4,5,6-Tetrafluoro-2-hydroxyphenyl)imidazopyridine (2) is demonstrated to have a high potential as a fluorescent chemosensor for a metal cation, which can signal a distinct wavelength emission corresponding to each captured metal cation. When 2 senses Zn^<2+> cation in acetonitrile solution, it causes the blue emission around 430 nm wavelength; and when 2 senses Al^<3+> and Hg^<2+>, it signals the sky blue emission around 370 nm wavelength. This ability is attributable to the complex in which the attached hydroxyl groups and the coordinated water molecules on the metal cation link via the hydrogen bondings to the 1-nitrogen atom and to the 2-fluorine atom of 2.