Developing fluorescence-improved fluoran dyes and applying for a copper selective and sensitive fluorescent probe and cell imaging

Developing fluoran dyes for fluorescent material is significant but challenging because they are notorious for terrible luminescent efficiency. In this manuscript, two fluoran dyes (F3 and F4) were synthesized by the introduction of thiazole and indazole into the fluoran skeleton, which showed colored and fluorescent spirolactone opening form in a wide pH range (F3: 1–10, F4: 1–13). In addition, the absorption and emission spectra of methyl esterification products F3Me and F4Me showed large Stokes shifts (over 75 nm) in water and achieved an improved fluorescence quantum yield of 30.1% in CHCl3. Based on the dye F4Me, a new fluorescent probe F4HP was developed, which showed high selectivity and high sensitivity (LOD of 2.0 nM) to copper ions in H2O/CH3CN (v/v, 3/2) system. Moreover, the sensing experiment was allowed in the pH range of 4.0–7.5. Furthermore, the F4HP exhibits suitable cell cytotoxicity and can be applied for imaging intracellular copper ions by confocal fluorescence imaging technology. Thiazole and indazole functionalized fluoran dyes were prepared with improved fluorescence and application in the construction of a novel copper-selective and sensitive fluorescent probe. [Display omitted] •Two modified fluoran dyes were prepared with stable fluorescence in water.•F4Me achieved a fluorescence quantum yield of 30.1% in CHCl3.•A novel probe F4HP for Cu2+ was prepared with high selectivity and sensitivity.•F4HP could be employed as a tool for imaging intracellular Cu2+.