Ultra-sensitive fluorescent and colorimetric probes for femtomolar detection of picric acid: Mechanochromic, latent fingerprinting, and pH responsive character with AIE properties

Multiple stimuli responsive easy to synthesize organic probes with remarkable structural properties are imminently essential. To this endeavor, 1,4-dihydropyridine (DHP) based three probes 1(a-c) were successfully synthesized and characterized through modern spectroscopic and mass spectrometry techniques. Planar dihydropyridine was appended with multiple donor-acceptor and rotors to bring aggregation induced emission (AIE) character in probes 1(a, b). Interestingly, probe 1c displayed aggregation caused quenching (ACQ) effect due to perpendicularly attached naphthyl ring. Therefore, this study presents extensive structure-property relationship to invoke AIE character. Moreover, probes 1(a-c) exhibited high photostability, reversible mechanochromism, pH responsive character, and adequate identification of latent fingerprints (LFPs). Importantly, multifunctional probes 1(a-c) served as highly selective fluorescent and colorimetric probes for picric acid (PA). In solution, highly sensitive femtomolar (fM) level (limit of detection (LOD); 12.3, 14.6, and 27.1 fM) detection of PA was attributed to combined effect of ground-state charge transfer complex formation and Forster resonance energy transfer (FRET). Favorable complexation between probes and PA was proved through UV-visible absorption, density functional theory (DFT), and dynamic light scattering (DLS) studies. Advantageously, probes were able to detect picric acid in vapor phase. In addition, probes were practically applicable for the contact mode detection of PA and sensing of PA in LFPs and industrial samples.

Automated summary

This study presents the synthesis and characterization of multiple stimuli responsive organic probes with remarkable structural properties. The probes exhibit aggregation induced emission and aggregation caused quenching effects. They also demonstrate high selectivity and sensitivity for the detection of picric acid, both in solution and in the vapor phase.