A quinoline-based heptadentate ligand, N,N,N',N'-tetrakis(2-quinolylmethyl)-2,6-bis(aminomethyl)pyridine (TQLN), exhibits a Zn-specific fluorescence increase at 428 nm, which is assigned to excimer emission (I/I = 38, I/I = 24%, ϕ = 0.069). In contrast, the isoquinoline counterpart 1-isoTQLN exhibits a Cd-specific fluorescence increase at 365 nm attributable to monomer emission (I/I = 83, I/I = 19%, ϕ = 0.015).

No abstract

Fluorescence detection of Zn 2 + and Cd 2 + is of continuing interest due to their significant importance in biological and environmental sciences. Strict discrimination of Zn 2 + and Cd 2 + by fluorescent probe molecules has still been a challenging task because of the small difference in ionic radii of these group 12 metal ions. In this study, three heptadentate fluorescent probes with a common 2,6-lutidylenediamine core and four quinoline/ isoquinoline sidearms are presented. The N,N,N',N'-tetrakis(2quinolylmethyl)-2,6-lutidylenediamine (TQLN) exhibits Zn 2 + -spe-cific fluorescence enhancement via an excimer formation, while the N,N,N',N'-tetrakis(1-isoquinolylmethyl)-2,6-lutidylenediamine (1-isoTQLN) responds specifically to Cd 2 + at the short wavelength region by monomer emission. The N,N,N', responds to both Zn 2 + and Cd 2 + at different emission wavelengths, acting as a dual sensor with hybrid properties of TQLN and 1-isoTQLN. Methoxy-substituted derivatives of 1-and 3-isoTQLN were also examined.