Anion-Exchange Induced Strong π–π Interactions in Single Crystalline Naphthalene Diimide for Nitroexplosive Sensing: An Electronic Prototype for Visual on-Site Detection

A new
derivative of naphthalene diimide (NDMI) was synthesized that displayed
optical, electrical, and visual changes exclusively for the most widespread
nitroexplosive and highly water-soluble toxicant picric acid (PA)
due to strong π–π interactions, dipole-charge interaction,
and a favorable ground state electron transfer process facilitated
by Coulombic attraction. The sensing mechanism and interaction between
NDMI with PA is demonstrated via X-ray diffraction analysis, 1H NMR studies, cyclic voltammetry, UV–visible/fluorescence
spectroscopy, and lifetime measurements. Single crystal X-ray structure
of NDMI revealed the formation of self-assembled crystalline network
assisted by noncovalent C–H···I interactions
that get disrupted upon introducing PA as a result of anion exchange
and strong π–π stacking between NDMI and PA. Morphological
studies of NDMI displayed large numbers of single crystalline microrods
along with some three-dimensional (3D) daisy-like structures which
were fabricated on Al-coated glass substrate to construct a low-cost
two terminal sensor device for realizing vapor mode detection of PA
at room temperature and under ambient conditions. Furthermore, an
economical and portable electronic prototype was developed for visual
and on-site detection of PA vapors under exceptionally realistic conditions.