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-Zn
2+ > BQClOH-Cd
2+ >> BQOH-Cd
2+ > BQOH-Zn
2+. 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 Zn
2+ complexes of quinoline chromophore, BQOH and BQClOH, in order to investigate the cause of the difference in the fluorescent intensity (BQClOH-M
2+ >> BQOH-M
2+, M
2+ = Zn
2+ or Cd
2+). The results of the calculations showed that the T
2 state of the [ZnBQO]
+ lay just below its S
1 state, while that was not the case for [ZnBQClO]
+.
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