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

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.

Cd2+-selective fluorescence response of TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) derivatives bearing ether oxygen-binding sites

“…S16-S19 †). 37,45,49 Fluorescence enhancement of TriMeO-8-MOMOTQEN in the presence of metal ions As described above, MOMO substitution to the zinc sensor TQEN afforded high Cd 2+ selectivity and fluorescence intensity. The fluorescence quantum yield of the cadmium complex of TriMeOBAPTQ was much higher (Chart 1, ϕ Cd = 0.19).…”

“…The formation of less-emissive, hydroxide-bridged dinuclear zinc complexes is also utilized in these systems. 23,34 The switching of fluorescent Zn 2+ /Cd 2+ selectivity by small alterations of the probe structure has also been discussed based on the hexadentate 35,36 or heptadentate 34,37 tetrakis(iso)quinoline platforms.…”

Effect of methoxy substituents on fluorescent Zn2+/Cd2+ selectivity of bisquinoline derivatives with a N,N′-dimethylalkanediamine skeleton

“…The TQEN platform is also useful for specific Zn 2+ detection [26][27][28] and in fact, quite small alterations in the molecular structure often reverse the fluorescent target metal ions between Zn 2+ and Cd 2+ . [29][30][31][32] Therefore, it is quite difficult and important to propose a general strategy for specific detection of Cd 2+ .…”