title: Multicolor fluorescence of a styrylquinoline dye tuned by metal cations.
abstract: A styrylquinoline dye with a dipicolylamine (DPA) moiety (1) has been synthesized. The dye 1 in acetonitrile demonstrates multicolor fluorescence upon addition of different metal cations. Compound 1 shows a green fluorescence without cations. Coordination of 1 with Cd(2+) shows a blue emission, while with Hg(2+) and Pb(2+) exhibits yellow and orange emissions, respectively. The different fluorescence spectra are due to the change in intramolecular charge transfer (ICT) properties of 1 upon coordination with different cations. The DPA and quinoline moieties of 1 behave as the electron donor and acceptor units, respectively, and both units act as the coordination site for metal cations. Cd(2+) coordinates with the DPA unit. This reduces the donor ability of the unit and decreases the energy level of HOMO. This results in an increase in HOMO-LUMO gap and blue shifts the emission. Hg(2+) or Pb(2+) coordinate with both DPA and quinoline units. The coordination with the quinoline unit decreases the energy level of LUMO. This results in a decrease in HOMO-LUMO gap and red shifts the emission. Addition of two different metal cations successfully creates intermediate colors; in particular, the addition of Cd(2+) and Pb(2+) at once creates a bright white fluorescence.
authors.affiliation: Research Center for Solar Energy Chemistry and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan. shiraish@cheng.es.osaka-u.ac.jp
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shiraishi
authors.forename: Chizuru
authors.initials: C
authors.lastname: Ichimura
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Sumiya
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hirai