| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2004: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2003: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2002: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
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.
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