Synthesis of novel triazine-quinoline-appended naphthalimide sensors for Hg(II) recognition and their structure-activity relationship

Constructing intelligent molecules for specific recognition of metal ions is critically important in environmental and biological fields. In this work, three novel triazine-quinoline-appended naphthalimide fluorescent sensors (NAK1, NAK2, NAK3) with different lengths of the linker were constructed. Research concerning the structure-fluorescence relationships of the three compounds showed that they exhibited distinct photophysical properties in either solution state or solid state. Compound NAK2, containing triazine-quinoline group with an ethylene (-CH2CH2-) linker, showed the strongest liquid state fluorescence emission, and it also displayed superior recognitive selectivity and sensitivity to Hg2+. NAK2 could detect Hg2+ within 2 min in phosphate buffer (PBS)/EtOH (v/v, 3/2) with low detection limit (0.045 mu mol/L), being applied in Hg2+ detection in environmental water samples. Job's plot, H-1 NMR and DFT calculations demonstrate that NAK2 combined with Hg2+ in 1:1 because of the special coordination holes, causing the change of planarity and electron transfer. This new type of molecular switch provides a new way of building high-performance fluorescence sensors.

Automated summary

Constructing intelligent molecules for specific recognition of metal ions is important in environmental and biological fields. The new fluorescent sensor NAK2 showed strong fluorescence emission and high sensitivity to Hg2+, providing a new way for building high-performance fluorescence sensors. NAK2 could detect Hg2+ in a short time with low detection limit, suitable for Hg2+ detection in environmental water samples.