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

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 Cr 3+ in CH 3 CN . Upon treatment with Cr 3+ , a strong emission was observed at 515 nm, but other metal ions, such as K + , Ag + , Ca 2+ , Zn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Cd 2+ , Hg 2+ , Fe 2+ , and Fe 3+ , failed to induce such an emission band. A clean isosbestic point appeared at 405 nm in the UV –vis titration with Cr 3+ . The emission intensity of EW1 was enhanced with incremental addition of Cr 3+ , indicating the formation of a 1:1 complex of the probe EW1 and chromium ion. However, EW1 showed a selective turn‐off response with Cu 2+ in CH 3 OH . The emission band of EW1 at 540 nm was quenched only with Cu 2+ 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 Cu 2+ . All spectroscopic titration experiments and ESI mass data provided evidence for the formation of a 1:1 complex between EW1 and Cu 2+ .