Fluorescent Calix[4]arene-Carbazole-Containing Polymers as Sensors for Nitroaromatic Explosives

Patrícia D Barata,José V Prata

doi:10.3390/chemosensors8040128

Abstract

Two highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-carbazolylene polymers (Calix-PPE-CBZs) were used in the detection of explosives from the nitroaromatic compounds (NACs) family, in solution and in vapour phases. Both fluorophores exhibit high sensitivity and selectivity towards NACs detection. The quenching efficiencies in solution, assessed through static Stern-Volmer constants (KSV), follow the order picric acid (PA) >> 2,4,6-trinitrotoluene (TNT) > 2,4-dinitrotoluene > (2,4-DNT) > nitrobenzene (NB). These correlate very well with the NACs electron affinities, as evaluated from their lowest unoccupied molecular orbitals (LUMOs) energies, indicating a photo-induced electron transfer as the dominant mechanism in fluorescence quenching. Moreover, and most interesting, detection of TNT, 2,4-DNT and NB vapours via thin-films of Calix-PPE-CBZs revealed a remarkably sensitive response to these analytes, comparable to state-of-the-art chemosensors. The study also analyses and compares the current results to previous disclosed data on the detection of NACs by several calix[4]arene-based conjugated polymers and non-polymeric calix[4]arenes-carbazole conjugates, overall highlighting the superior role of calixarene and carbazole structural motifs in NACs’ detection performance. Density functional theory (DFT) calculations performed on polymer models were used to support some of the experimental findings.

Highlights

Development of chemical sensors and devices thereof for trace detection of high explosives is a very active area of research given the potential of this approach to increase anti-terrorism actions and homeland security, to help foster secure methodologies for hidden landmines detection and, in general, to assist environmental and forensic investigations related to explosive materials [1,2,3,4].development of fast and ultra-sensitive detection devices for explosive materials is critical to ensuring global security
Very precise methods exist for Nitroaromatic compounds (NACs) detection and quantification, which rely on several well-established techniques (e.g., surface enhanced Raman spectroscopy (SERS), ion mobility spectrometry (IMS), gas chromatography-electron capture detection (GC/ECD) and electrospray ionization-liquid chromatography/mass spectrometry (ESI-LC/MS)), they are usually quite expensive, time-consuming and/or lack the portability required for in-field applications [5,6]
Gel permeation chromatography (GPC) allowed the determination of the polymers’ weight-average molecular weights (Figure S3), which range from 8000 g·mol−1 (Mw /Mn = 1.73; average degree of polymerisation (DP) ≈ 2) for

Summary

Introduction

Development of chemical sensors and devices thereof for trace detection of high explosives is a very active area of research given the potential of this approach to increase anti-terrorism actions and homeland security, to help foster secure methodologies for hidden landmines detection and, in general, to assist environmental and forensic investigations related to explosive materials [1,2,3,4].development of fast and ultra-sensitive detection devices for explosive materials is critical to ensuring global security. Very precise methods exist for NACs detection and quantification, which rely on several well-established techniques (e.g., surface enhanced Raman spectroscopy (SERS), ion mobility spectrometry (IMS), gas chromatography-electron capture detection (GC/ECD) and electrospray ionization-liquid chromatography/mass spectrometry (ESI-LC/MS)), they are usually quite expensive, time-consuming and/or lack the portability required for in-field applications [5,6]. In this context, Chemosensors 2020, 8, 128; doi:10.3390/chemosensors8040128 www.mdpi.com/journal/chemosensors

Methods

Results

Conclusion