N,N,N′,N′‐Tetrakis(3‐isoquinolylmethyl)‐2,6‐lutidylenediamine (3‐isoTQLN): A Fluorescent Zn2+/Cd2+ Dual Sensor as a Hybrid of 2‐Quinolyl/1‐Isoquionolyl Counterparts TQLN/1‐isoTQLN

Fluorescence detection of Zn2+ and Cd2+ is of continuing interest due to their significant importance in biological and environmental sciences. Strict discrimination of Zn2+ and Cd2+ 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(2‐quinolylmethyl)‐2,6‐lutidylenediamine (TQLN) exhibits Zn2+‐specific fluorescence enhancement via an excimer formation, while the N,N,N′,N′‐tetrakis(1‐isoquinolylmethyl)‐2,6‐lutidylenediamine (1‐isoTQLN) responds specifically to Cd2+ at the short wavelength region by monomer emission. The N,N,N′,N′‐tetrakis(3‐isoquinolylmethyl)‐2,6‐lutidylenediamine (3‐isoTQLN) responds to both Zn2+ and Cd2+ 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. 3‐isoTQLN (N,N,N′,N′‐tetrakis(3‐isoquinolylmethyl)‐2,6‐lutidylenediamine), which has four isoquinoline moieties attached to a pyridine‐containing diamine core, acts as a dual sensor for Zn2+ and Cd2+ with fluorescence response at different wavelengths.