A turn-on fluorescent chemosensor for Zn2+ ion: X-ray structure and application in cell imaging study

• 2-methoxy-6-(2-morpholinoethyliminomethyl)phenol (HL) explored as sensor for Zn2+.
• The emission intensity of HL enhanced ∼ 25 times in the presence of one eqv. of Zn2+.
• Limit of detection of HL for Zn2+ determined as low as 40.5 nM.
• Formed 1:1 complex with Zn2+ and confirmed by X-ray single crystal diffraction study.
• Used for imaging of DLD-1, human colorectal adenocarcinoma cell.

The selective fluorescence zinc(II) sensing properties of a Schiff-base compound, 2-methoxy-6-(2-morpholinoethyliminomethyl)phenol (HL) have been explored. The emission intensity of HL in the presence of one equivalent of Zn2+ ion increases by about 25 times. Several other metal ions, except Cd2+ and Ni2+, have not been able to increase the emission intensity of HL significantly. The quantum yield and life-time of HL have also been increased in the presence of Zn2+ ions. The enhancement in fluorescence intensity of HL is mainly due to the restriction of ESIPT, CHEF and PET on complex formation. HL forms a complex with Zn2+ in 1:1 ratio as evidenced by Job's plot analysis and X-ray single crystal structure determination. Some theoretical calculations have been performed to get a better view on the nature of the observed electronic transitions. The probe has been applied for imaging of DLD-1, human colorectal adenocarcinoma cell.