A new near-infrared fluorescence sensor based on dicyanomethylene-4H-pyran for the detection of Al3+, Cr3+, Fe3+and Cu2+

A novel near-infrared (NIR) fluorescence sensor DCM-PSI based on dicyanomethylene-4H-pyran(DCM) was designed and synthesized to selectively detect Al3+, Cr3+, Fe3+ and Cu2+. It had a large Stokes shift (lambda abs = 450 nm, lambda ex = 490 nm, lambda em = 690 nm), low detection limits and large binding constants. With the addition of Al3+, Cr3+, Fe3+ and Cu2+, the fluorescence quenched and the emission peaks blue shifted to different extent. Experimental analysis and quantum chemical calculations showed that the luminescence of DCM-PSI experienced an excited state intramolecular proton transfer (ESIPT) and partly intramolecular charge transfer (ICT) process, while the complexation of Al3+, Cr3+, Fe3+ and Cu2+ caused ligand-to-metal electron transfer, and altered the "push-pull" effect in DCM-PSI. Furthermore, the Al3+ and Fe3+ in drinking water was also measured with DCM-PSI to test the practical application of the sensor.