Nickel(II)-Induced Excimer Formation of a Naphthalene-Based Fluorescent Probe for Living Cell Imaging

Abstract

Ni²⁺-induced intramolecular excimer formation of a naphthalene-based novel fluorescent probe, 1-[(naphthalen-3-yl)­methylthio]-2-[(naphthalen-6-yl)­methylthio]­ethane (<b>L</b>), has been investigated for the first time and nicely demonstrated by excitation spectra, a fluorescence lifetime experiment, and ¹H NMR titration. The addition of Ni²⁺ to a solution of <b>L</b> (DMSO:water = 1:1, v/v; λ_em = 345 nm, λ_ex = 280 nm) quenched its monomer emission, with subsequent enhancement of the excimer intensity (at 430 nm) with an isoemissive point at 381 nm. The fluorescence lifetime of free <b>L</b> (0.3912 ns) is much lower than that of the nickel­(2+) complex (1.1329 ns). <b>L</b> could detect Ni²⁺ as low as 1 × 10^–6 M with a fairly strong binding constant, 2.0 × 10⁴ M^–1. Ni²⁺-contaminated living cells of plant origin could be imaged using a fluorescence microscope