Fluorescent properties and probe features of newly synthesized acridine-terpyridyl bidentate ligand and its metalated complexes

Photoactive organic ligands and their metalated complexes are important luminophors and potential sensing or probing materials in the fields of optical displays, sensors, toxicant detection and biological imaging. Here, we report synthesis, photophysical properties and fluorescent probe features of an acridine-terpyridyl (AcTPy) bidentate ligand and its metalated complexes. Different from the other metal ions, the zinc-metalated AcTPy complex displays a strong yellow luminescence with a broad emission band at 500–570 nm, suggesting that this bidentate ligand can be used as a fluorescent probe for the zinc ions. Based on this feature, we have synthesized several zinc-AcTPy complexes. These complexes give off two strong fluorescent emissions centered at approximately 408 and 535 nm; the former one attributed to the electron transfer from the excited terpyridyl (TPy) substituent and the latter one to that of the acridine. Further, it is revealed that the fluorescent emissions of Zn-AcTPy complexes are dependent on the excited wavelengths, solvents and protons (organic acids) co-existed. The acidity dependence is attributed to the protonation effect of acridine substituent in the acidic solution. Finally, the fluorescent emission band of Zn-AcTPy complexes shifts to approximately 450 nm when co-existed with Cd2+ ion, attributed to coordination bonding of Cd2+ ion with the N atom of acridine unit. The detection limit for the Cd2+ ions is estimated to be approximately 90 nmol/L. Hence, based on the fluorescent features of the zinc-AcTPy complexes, we can suggest that the present AcTPy bidentate ligand and its metalated complexes can be used as the fluorescent probes for protons, Zn2+ and Cd2+ ions.