Luminescent Metal–Organic Nano Probes with a Sulfone Moiety Synthesized at Room Temperature for Ultrafast Detection of Organic Pollutants in Aqueous Medium at the ppb Level

We report four sulfone-functionalized metal–organic
nano
probes synthesized at room temperature, [Zn2(3,7-DBTDC)2(bpma)2] (1), {[Cd(3,7-DBTDC)(bpma)]·H2O}n (2), [Zn2(3,7-DBTDC)2(bpta)2]·2H2O (3), and {[Cd(3,7-DBTDC)(bpta)]·4H2O}n (4), employing pyridyl
ancillary ligands, like N,N′-bis(pyridylmethyl)methylamine
(bpma) and N,N′-bis(pyridylmethyl)tertiarybutylamine
(bpta), and a rigid π-electron rich linker, benzothio-phene-5,5′-dioxide-3,7-dicarboxylate
(3,7-DBTDC2–). The single-crystal structure analysis
that was possible for 2–4 reveals
that 2 and 4 have a similar 1D helical structure,
while 3 has a bis(3,7-DBTDC)-bridged dinuclear structure
that forms a supramolecular assembly through moderate π···π
interactions leading to face-to-face stacking of the aromatic rings.
Similar π···π interactions are observed
between the 1D helical chains of 4 forming a 2D supramolecular
assembly. A thorough spectroscopic, microscopic, and elemental analysis
of these probes was conducted to confirm their bulk purity and morphology
and to establish their physicochemical properties. Utilizing the sulfone
functional group of the probes as interaction sites, 1–4 are found to be excellent recyclable probes
for the detection of 4-nitroaniline (4-NA) and 2,4,6-trinitrophenol
(TNP) in aqueous medium within 20 s providing the limit of detection
as low as 125 and 364 ppb, respectively, with significantly high quenching
constants and selectivity. Additionally, the naked-eye detection of
4-NA and TNP made in Milli-Q and tap water is presented. The quenching
mechanism was established through experimental and theoretical supports.