A Solvent-dependent Fluorogenic Probe Containing Julolidine for Cr(III) and Cu(II)

Abstract

A julolidine-containing naphthylamine probe (EW1) was prepared for sensing specific metal ions. Probe EW1 afforded a broad low fluorescence at 500-600 nm in acetonitrile, but gave a relatively stronger fluorescence at 540 nm in methanol. EW1 showed a selective turn-on emission for Cr3+ in CH3CN. Upon treatment with Cr3+, a strong emission was observed at 515 nm, but other metal ions, such as K+, Ag+, Ca2+, Zn2+, Co2+, Ni2+, Cu2+, Cd2+, Hg2+, Fe2+, and Fe3+, failed to induce such an emission band. A clean isosbestic point appeared at 405 nm in the UV-vis titration with Cr3+. The emission intensity of EW1 was enhanced with incremental addition of Cr3+, indicating the formation of a 1: 1 complex of the probe EW1 and chromium ion. However, EW1 showed a selective turn-off response with Cu2+ in CH3OH. The emission band of EW1 at 540 nm was quenched only with Cu2+ and not with other control metal ions. The absorption band of EW1 at 410 nm progressively decreased, and a new absorption at 390 nm appeared upon progressive addition of Cu2+. All spectroscopic titration experiments and ESI mass data provided evidence for the formation of a 1: 1 complex between EW1 and Cu2+.