Zinc-Specific Fluorescent Response of Tris(isoquinolylmethyl)amines
(isoTQAs)
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Abstract
Isoquinoline-based tetradentate ligands with <i>C</i><sub>3</sub>-symmetry, tris(1- or 3-isoquinolylmethyl)amine
(1- or 3-isoTQA), have been
prepared and their zinc-induced fluorescence
enhancement was investigated. Upon excitation at 324 nm,
1-isoTQA shows very weak fluorescence (ϕ = ∼0.003) in
DMF/H<sub>2</sub>O (1/1) solution. In the presence of zinc ion, 1-isoTQA
exhibits fluorescence increase (ϕ = 0.041)
at 359 and 470 nm. This fluorescence enhancement at 470
nm is specific for zinc. However, 3-isoTQA exhibited a smaller fluorescence
enhancement upon zinc complexation (ϕ = 0.017, λ<sub>em</sub> = 360 and 464 nm) compared with 1-isoTQA. Crystal structures of
zinc complexes of isoTQAs demonstrate the diminished steric crowding
and shorter Zn–N<sub>aromatic</sub> distances compared with
isoTQENs (<i>N,N,N′,N′</i>-tetrakis(isoquinolylmethyl)ethylenediamines)
leads to a higher fluorescent response toward zinc relative to cadmium
