Pyreneamide-based dipodal probes for ultra-sensitive and selective detection of 3,5-dinitrosalicylic acid in an aqueous solution

Abstract

Pyrene-appended dipodal probes (probes 1 and 2) with differences in conformational rigidity were synthesized for sensitive detection of 3,5-dinitrosalicylic acid (DNSA) in an aqueous solution. Both dipodal probes had two pyrene units and exhibited quenching caused by aggregation (ACQ) at high water content (>60%) in DMSO. As the pyrene dimer (e.g., excimer) was a dominant conformation in 99% aqueous solution, both probes showed sufficient excimer emission intensity at 486 nm (probe 1) or 480 nm (probe 2) upon excitation. The excimer emission of the probes (probes 1 and 2) was sensitively quenched in the presence of DNSA. Probe 1 selectively responded to DNSA among various carboxylic acids (CAs), while probe 2 was responsive to both DNSA and 5-NSA. Density functional theory (DFT) calculations suggest that, in the presence of DNSA, the probes undergo structural changes, leading to formation of new pi-pi interactions between each pyrene unit of the probe and the benzene ring of the guest molecule. This new pi-pi interaction enabled energy transfer from pyrene to the non-radiative guest molecule (DNSA), resulting in fluorescence quenching in the probes. The limit of detection (LOD) of probe 1 with DNSA was observed to be 1 nM, the lowest value reported so far. This ultra sensitivity toward DNSA detection was retained even in the case of a probe 1-coated TLC strip. Probe 3, which had only one pyrene unit, gave produced a monomeric emission spectrum with lambda(max) = 406 nm, along with aggregation-induced emission enhancement (AIEE) behavior. The interactions of DNSA with individual probes were examined by UV-visible, fluorescence, and H-1 NMR spectroscopies and were further supported by DFT calculations. (C) 2017 Published by Elsevier Ltd.