title: OFF-ON-OFF fluorescent response of N,N,N',N'-tetrakis(1-isoquinolylmethyl)-2-hydroxy-1,3-propanediamine (1-isoHTQHPN) toward Zn(2.).
abstract: An isoquinoline-based ligand, N,N,N',N'-tetrakis(1-isoquinolylmethyl)-2-hydroxy-1,3-propanediamine (1-isoHTQHPN), exhibits a fluorescence increase at 475 nm upon addition of 1 equiv. of Zn(2+) (IZn/I0 = 12, ϕZn = 0.023). This fluorescence enhancement turns and then decreases sharply after the addition of more than 1 equiv. of Zn(2+) reaching a constant minimum intensity with more than 2 equiv. of Zn(2+). In contrast, the fluorescence intensity at 353 nm continues to increase until the signal saturates at ca. 5 equiv. of Zn(2+). This observation can be explained by the formation of a fluorescent mononuclear complex ([Zn(1-isoHTQHPN)](2+)) followed by a non-fluorescent dinuclear complex ([Zn2(1-isoTQHPN)](3+)) at 475 nm during the titration of 1-isoHTQHPN with Zn(2+). Both the mono- and dinuclear complexes were characterized by UV-vis, fluorescence, (1)H NMR, ESI-MS, X-ray crystallography and TDDFT calculations. The fluorescence enhancement at 475 nm is Zn(2+)-specific; Cd(2+) induces a much smaller emission increase (ICd/I0 = 3.7, ICd/IZn = 31%). The Zn(2+)/Cd(2+) selectivity of the fluorescent response correlates with the difference in excimer-forming ability derived from the Cd-Nisoquinoline and Zn-Nisoquinoline bond distances.
authors.affiliation: Department of Chemistry, Biology, and Environmental Science, Faculty of Science, Nara Women's University, Nara 630-8506, Japan. mikata@cc.nara-wu.ac.jp and KYOUSEI Science Center, Nara Women's University, Nara 630-8506, Japan and Department of Chemistry, Faculty of Science, Nara Women's University, Nara 630-8506, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Mikata
authors.affiliation: Department of Chemistry, Faculty of Science, Nara Women's University, Nara 630-8506, Japan.
authors.forename: Risa
authors.initials: R
authors.lastname: Ohnishi
authors.affiliation: Department of Chemistry, Faculty of Science, Nara Women's University, Nara 630-8506, Japan.
authors.forename: Anna
authors.initials: A
authors.lastname: Ugai
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Konno
authors.affiliation: Horiba, Ltd, 2 Miyanohigashi, Kisshoin, Minami-ku, Kyoto 601-8510, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nakata
authors.affiliation: Horiba, Ltd, 2 Miyanohigashi, Kisshoin, Minami-ku, Kyoto 601-8510, Japan.
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hamagami
authors.affiliation: Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Sato