| Co-Investigator(Kenkyū-buntansha) |
HOSHINO Hitoshi Tohoku University, Graduate School of Environmental Studies, Professor, 大学院環境科学研究科, 教授 (20124620)
TAKAHASHI Toru Tohoku University, Graduate School of Environmental Studies, Research Assistant, 大学院環境科学研究科, 助手 (30361166)
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| Research Abstract |
Probes with long-lived luminescence in near-infrared region were obtained with supramolecular formation in lanthanide(III)-silver(I)-thiacalix[4]arene-p-tetrasulfonate (TCAS) ternary systems via following studies.
1.Structural characterization of Tb(III)-Ag(I)-TCAS supramolecular complex with ES-MS : It was clarified that supramolecular complex Ag_2・Tb_2・TCAS (1) was formed at pH 6.5, whereas Ag_2・Tb・TCAS (2) was formed at pH 10.0. Complexes 1 and 2 adopted double-cone structures, in which two Ag(I) ions bridges two cone-shaped TCAS by Ag(I)-S-Ag(I) bridges. In complex 1, TCAS coordinate to Tb(III) with two sets of O,S,O-coordination, whereas in complex 2 each TCAS coordinate to Tb(III) center with two sets of O,O,O,O-coordination.
2.Determination of photophysical properties : For complex 1, determined parameters are as follows: luminescence quantum yield Φ = 0.16, luminescence lifetime τ= 1.09 ms, and number of coordinating water to Tb(III) q = 2.4. For complex 2, Φ (=0.11) was smaller
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than that of 1, but τ (= 4.61 ms) was as large as intrinsic luminescence lifetime of Tb(III) ion (4.7 ms). This owes to the fact that number of coordinating water was almost zero (q = 0.1). Removal of coordinating water from lanthanide center is a key to realize NIR luminescence in aqueous solutions, because coordinating water strongly quenches NIR luminescence via high-energy vibrational modes. Therefore, we selected supramolecular complex 2 as a candidate for NIR probe.
3.Characterization of NIR probes : Yb(III) ion formed supramolecule 2 at pH 9.9, which emitted MIR light at 983 nm with Φ = 2.5x10^<-3>. On the other hand, Nd(III) formed Ag_3 Td TCAS (3) under the same conditions, which exhibited luminescence at 1050 nm (0=2.9x 10^<-4>).
4.Elucidation of kinetic stability : Solvolytic dissociation rate constant for Ag_2 Tb TCAS.( was determined to be 3.1x10^<-3> s^<-1> with a capillary electrophoretic reactor. This corresponds to half-life of 3.8 min, which is rather small from a view point of biological application. It was concluded that improvement of kinetic stability is next challenge for practical application of supramolecular NIR-luminescence probes. Less
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