Time-Dependent DFT Study of Emission Mechanism of 8-Hydroxyquinoline Derivatives as Fluorescent Chemosensors for Metal Ions

Ryo MIYAMOTOa*, Jun KAWAKAMIa*, Shuko TAKAHASHIa, Shunji ITOa, Masahiko NAGAKIa and Haruo KITAHARAb

aDepartment of Materials Science and Technology, Faculty of Science and Technology, Hirosaki University,
Bunkyo-cho 3, Hirosaki, Aomori 036-8561, Japan
bDepartment of Natural Science, Faculty of Education, Hirosaki University
Bunkyo-cho 1, Hirosaki, Aomori 036-8560, Japan

(Received: April 14, 2005; Accepted for publication: August 25, 2005; Published on Web: December 28, 2005)

8-Hydroxyquinoline derivatives (BQOH and BQClOH) were synthesized as fluorescent chemosensors for metal ions. BQOH and BQClOH hardly show fluorescence themselves, but they showed strong fluorescence with the addition of zinc or cadmium ions. The order of the maximum values of fluorescence intensity (If,max) was BQClOH-Zn2+ > BQClOH-Cd2+ >> BQOH-Cd2+ > BQOH-Zn2+. Therefore, the ab initio calculations (by Gaussian 98) using the time-dependent density functional method with 6-31+G(d) basis set were carried out on the Zn2+ complexes of quinoline chromophore, BQOH and BQClOH, in order to investigate the cause of the difference in the fluorescent intensity (BQClOH-M2+ >> BQOH-M2+, M2+ = Zn2+ or Cd2+). The results of the calculations showed that the T2 state of the [ZnBQO]+ lay just below its S1 state, while that was not the case for [ZnBQClO]+.

Keywords: Time-dependent DFT, Quinoline, Metal ion recognition, Fluorescent chemosensor

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