Design and Development of Fluorescent Sensors with Mixed Aromatic Bicyclic Fused Rings and Pyridyl Groups: Solid Mediated Selective Detection of 2,4,6-Trinitrophenol in Water

Abstract

For a strategic incorporation of both π-electron-rich moieties and Lewis basic moieties acting as hydrogen bonding recognition sites in the same molecule, two new fluorescent sensors, N , N ′-bis(anthracen-9-ylmethyl)- N , N ′-bis(pyridin-2-ylmethyl)butane-1,4-diamine ( banthbpbn , 1 ) and N , N ′-bis(naphthalen-1-ylmethyl)- N , N ′-bis(pyridin-2-ylmethyl)butane-1,4-diamine ( bnaphbpbn , 2 ), have been developed for the selective detection of highly explosive 2,4,6-trinitrophenol (TNP) in water. Each of the two identical ends of these sensors that are linked with a flexible tetra-methylene spacer contains a mixed aromatic bicyclic fused ring (anthracene or naphthalene) and a pyridyl group. These are synthesized via the simple reduced Schiff base chemistry, followed by the nucleophilic substitution reaction under basic conditions in high yields. Both 1 and 2 were characterized by Fourier transform infrared, UV–vis, and NMR ( 1 H and 13 C) spectroscopy, and high-resolution mass spectrometry. The bulk phase purity of 1 and 2 and their stability in water were confirmed by powder X-ray diffraction (PXRD). Utilizing the effect of solvents on their emission spectra as determined by fluorescence spectroscopy, spectral responses for 1 and 2 toward various nitro explosives were recorded to determine a detection limit of 0.6 and 1.6 ppm, respectively, for TNP in water via the “turn-off” quenching response. Also, the detailed mechanistic investigation for their mode of action through spectral overlap, lifetime measurements, Stern–Volmer plots, and density functional theory calculations reveals that resonance energy transfer and photoinduced electron transfer processes, and electrostatic interactions are the key aspects for the turn-off response toward TNP by 1 and 2 . In addition, the selectivity for TNP has been found to be more in 1 compared to 2 . Both exhibit good recyclability and stability after sensing experiments, which is confirmed by PXRD and field-emission scanning electron microscopy.

Design and Construction of a Luminescent and Highly Stable 3D Metal–Organic Framework with a [Zn4(μ3-OH)2]6+Core

“…Also, the detection of NAs has gained considerable attention because of their toxicity and high solubility in water . These chemicals are found to be core components of various industrial explosives and environmentally deleterious substances; therefore, effective detection of NAs is crucial for security and environmental concerns. − …”

Quinoline-tagged fluorescent organic probes for sensing of nitro-phenolic compounds and Zn2+ions at the ppb level

“…70b Also, the detection limit of 2 is higher and comparable with other probes performed in water such as organic probes: H 2 ATAIA (120 ppb), 32 [45][46][47][48][49] The K SV values of 1 and 2 are higher than other reported organic probes such as probes tagged with naphthalene (3.43 Â 10 3 M À1 and 2.69 Â 10 4 M À1 ), 24,25 benzimidazole (1.58 Â 10 4 M À1 ), 27 anthracene (1.77 Â 10 4 M À1 ) 16 and fluorescein (2.10 Â 10 4 M À1 ) 31 and comparable with that of other anthracene (8.08 Â 10 4 M À1 and 7 Â 10 4 M À1 ), 25,32 fluorene (3.90 Â 10 4 M À1 ) 16 and MOF probes such as [Tb(BTC)] n (3.9 Â 10 4 M À1 ), 49c {Zr 6 O 4 (OH) 4 (L) 6 } n (2.9 Â 10 4 M À1 ), 45 [Cd(NDC) 0.5 (PCA)] n (3.9 Â 10 4 M À1 ) 40 and TB-Zn-CP (4.37 Â 10 4 M À1 ) 49d based sensors (Table S4, ESI †). On comparing the detection limits with the two sensors recently reported by our group, 62 it was observed that the sensing ability is improved by the variation of the spacer and increasing Lewis basic nitrogen sites. In addition, the K SV value of 1 is higher than its naphthalene analogue (3.26 Â 10 4 M À1 ).…”

“…This non-linearity can be allocated to self-absorption or an energy transfer process between the sensor and analyte. 1,32,62 In comparison, the SV plots for other analytes are almost a linear curve, thereby suggesting that either static or dynamic quenching is involved. 72 For TNP, the K SV values were found to be (3.55 AE 0.09) Â 10 4 and (4.97 AE 0.08) Â 10 4 M À1 , respectively in 1 and 2 (Fig.…”

“…In addition, the K SV value of 1 is higher than its naphthalene analogue (3.26 Â 10 4 M À1 ). 62 To further introspect into the sensing mechanism, the extent of spectral overlap between the absorbance spectra of the NACs (0.03 mM) and the emission spectra of 1 and 2 was analysed.…”

“…Recently, we have reported two fluorescent sensors based on naphthalene and anthracene fused rings along with pyridyl moieties connected by a tetra-methylene spacer and demonstrated their role in TNP detection. 62 This study provided a platform to design different fluorescent sensors with some variation and increase the sensing capabilities towards TNP.…”