Ultratrace
Detection of Nitroaromatics: Picric Acid Responsive Aggregation/Disaggregation
of Self-Assembled <i>p</i>‑Terphenylbenzimidazolium-Based
Molecular Baskets
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Abstract
1-(<i>p</i>-Terphenyl)-benzimidazolium
(TRIPOD-TP) molecules undergo self-assembly to form rodlike structures
in aqueous medium, as shown by field-emission scanning electron microscopy,
transmission electron microscopy, and dynamic light scattering studies.
Upon gradual addition of picric acid (PA), these aggregates undergo
an aggregation/disaggregation process to complex morphological structures
(10<sup>–12</sup>–10<sup>–10</sup> M PA) and
spherical aggregates (10<sup>–9</sup>–10<sup>–8</sup> M PA). These spherical aggregates undergo further dissolution to
well-dispersed spheres between 10<sup>–7</sup>–10<sup>–6</sup> M PA. During fluorescence studies, these aggregates
demonstrate superamplified fluorescence quenching (>97%) in the
presence of 10<sup>–5</sup> to 0.2 equiv of the probe concentration,
an unprecedented process with PA. The lowest detection limits by solution
of TRIPOD-TP are 5 × 10<sup>–13</sup> PA, 50 × 10<sup>–12</sup> M 2,4-dinitrophenol, 200 × 10<sup>–12</sup> M 2,4,6-trinitrotoluene, and 1 nM 1-chloro-2,4-dinitrobenzene. Paper
strips dipped in the solution of TRIPOD-TP demonstrate quantitative
fluorescence quenching between 10<sup>–17</sup> and 10<sup>–6</sup> M PA using front-surface steady state studies and
can measure as low as 2.29 × 10<sup>–20</sup> g/cm<sup>2</sup> PA