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

合成了含咪唑基团的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复合化学传感器，加入Al^&lt；3&gt；3&gt；2&gt；或Mg^&lt；2&gt；在氯仿-乙腈溶液中产生绿色发射和微弱的蓝光发射，两者的增强比与捕获的金属阳离子有关。绿色发射归因于金属阳离子与咪唑氮原子的连接，由此产生的氮原子的正性被感应地传递到羟基上，恢复其氢键能力，导致激发态分子内质子转移(ESIPT)过程。2-(2-氨基氟苯基)苯并恶唑类化合物，特别是2-(2-五氟苯甲胺基-3，4，5，6-四氟苯基)苯并恶唑类化合物的绿色发光更明显。绿色发射在非极性溶剂中被增强，导致相当大的斯托克斯位移。此外，取代苯并恶唑环系，合成了相应的由咪唑并吡啶环系构成的荧光团，并揭示了它们的识别能力。2-(3，4，5，6-Tetrafluoro-2-hydroxyphenyl)imidazopyridine(2)作为金属阳离子的荧光化学传感器具有很高的潜力，它可以发出与每个捕获的金属阳离子对应的不同波长的发射信号。当2在乙腈溶液中检测到锌离子时，它在430 nm附近产生蓝色发射，当2检测到Al^&lt；3&gt；和Hg^&lt；2&gt；时，它在370 nm附近发出天蓝色发射。这种能力归因于络合物，其中连接的羟基和金属阳离子上的配位水分子通过氢键与1-氮原子和2-氟原子相连。

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.