Isoquinoline-Based TQEN Family as TPEN-Derived Fluorescent Zinc Sensors

Abstract

The hexadentate nitrogen ligands 1-isoTQEN ( N,N,N',N'-tetrakis(1-isoquinolylmethyl)ethylenediamine) and 3-isoTQEN ( N,N,N',N'-tetrakis(3-isoquinolylmethyl)ethylenediamine) have been prepared. The structures of these ligands are based on that of TPEN ( N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine). The introduction of a benzene ring into TPEN affords fluorescence ability upon zinc-ion binding. Compared to the quinoline isomer TQEN, isoquinoline derivatives 1-isoTQEN and 3-isoTQEN exhibit a lower-energy shift in the excitation and emission wavelengths and an enhanced fluorescence intensity, probably because of the energy-transfer mechanism between adjacent isoquinoline rings. Importantly, an increase in the Zn (2+)/Cd (2+) discriminating ability and a reduction in the background fluorescence induced by pH were also achieved for isoquinoline derivatives. The zinc-ion-induced fluorescence of these isoTQENs was not quenched by an addition of TPEN, which demonstrates the significantly high zinc-ion binding ability of these isoTQEN ligands.

Synthesis, structure, and luminescence properties of complex ZnLClb2 (L is 2-(3,5-dimethylpyrazol-1-yl)-4-methylquinoline)

“…3 The luminescent Zn II complexes with different organic ligands were obtained. These ligands include fragments of nitrogenous heterocycles 3 contain ing π bonds, particularly pyridine, 4-7 quinoline, 8, 9 and benzimidazole. 10 A Zn II complex with a ligand including fragments of both pyrazole and benzimidazole was de scribed.…”

Chelate Ring Size Effect as a Factor of Selective Fluorescent Recognition of Zn2+Ions by Pyrrolo[2,3-b]quinoxaline with a Substituted 2-Pyridyl Group Receptor

“…14,16,19 In this paper, we demonstrate that the introduction of an ethylene spacer in 3 alters the photophysical properties and changes the coordination cavity size for Zn 2+ and Cd 3+ compared with conjugated 2.…”

“…The expansion of the chelate ring size from fivemembered in DQPMA to six-membered in DQPEA produces an increase in the selectivity for Zn 2+ over Cd 2+ . 16 We previously designed selective ICT ratiometric fluorescent receptors for zinc ions based on the E/Z diastereoisomers of Narylpyrrolo[2,3-b]quinoxaline or pyrido [2,3-b]pyrrolo[2,3-e]-pyrazine integrated with an amino alcohol, diaminoalkane, or 2-(2-aminoethyl)pyridine. 20−22 The fluorophore has a donor− acceptor architecture with an electron-donating enamino group and an electron-withdrawing amide moiety.…”

Development of a simple pyrazine-derived “turn on” Al 3+ fluorescent sensor with high selectivity and sensitivity

“…Ethyl 2-(quinolin-8-yloxy) acetate (2) and 2-(quinolin-8-yloxy) acetohydrazide (3) were prepared by the reported method [32]. A solution of the 2-(quinolin-8-yloxy) acetohydrazide (0.199 g, 0.968 mmol) in ethanol was added to a solution containing acetyl pyrazine (0.118 g, 0.968 mmol) in ethanol.…”