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Ultratrace Detection of Nitroaromatics: Picric Acid Responsive Aggregation/Disaggregation of Self-Assembled p‑Terphenylbenzimidazolium-Based Molecular Baskets

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journal contribution
posted on 20.05.2015, 00:00 by Sana Sandhu, Rahul Kumar, Prabhpreet Singh, Aman Mahajan, Manmeet Kaur, Subodh Kumar
1-(p-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 (10–12–10–10 M PA) and spherical aggregates (10–9–10–8 M PA). These spherical aggregates undergo further dissolution to well-dispersed spheres between 10–7–10–6 M PA. During fluorescence studies, these aggregates demonstrate superamplified fluorescence quenching (>97%) in the presence of 10–5 to 0.2 equiv of the probe concentration, an unprecedented process with PA. The lowest detection limits by solution of TRIPOD-TP are 5 × 10–13 PA, 50 × 10–12 M 2,4-dinitrophenol, 200 × 10–12 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 10–17 and 10–6 M PA using front-surface steady state studies and can measure as low as 2.29 × 10–20 g/cm2 PA.