Quantitative real time sensing reveals enhanced sensitivity of polar dendrimer thin films for plastic explosive taggants

Abstract

A method of introducing pulses of analyte vapours has been developed to study the interactions of nitrocontaining analytes with fluorescent sensing films. The quenching of the photoluminescence of thin dendrimer films by exposure to sub-saturation concentration vapour pulses of nitro-containing analytes is quantified and the reversibility of quenching interactions qualitatively examined. The analysis reveals a linear dependence of the initial/quenched fluorescence ratio (F 0 /F) with quencher concentration akin to Stern-Volmer behaviour routinely used to quantify quenching efficiency in solution. Detection limits and quenching efficiencies were calculated in the sub-saturation regime for each of the analytes and tracelevel detection of 1,4-dinitrobenzene, 2,4-dinitrotoluene, 4-nitrotoluene, and nitromethane vapours was observed. It was found that the sensitivity of first generation bifluorene-and carbazole-cored dendrimers towards vapours of the nitroaliphatic taggant 2,3-dimethyl-2,3-dinitrobutane was significantly enhanced by changing the solubilising chains on the core from alkyl to oligo(ethylene oxide) groups. The responses of the films were observed to be independent of film exposure history making these dendrimers interesting candidates for deployment in thin film vapour sensors for explosives. † Electronic supplementary information (ESI) available: The experimental details for the synthesis and characterisation of the dendrimer precursors 1 and 3b is detailed. See

High-Sensitivity Poly(dendrimer)-Based Sensors for the Detection of Explosives and Taggant Vapors

“…This is an interesting result, as the difficulty in detecting DMNB often arises from the fact that its diffusion out of the film is rapid, meaning that the analyte concentration in the film is low and PL responses weak and difficult to distinguish from the baseline. P2 showed the greatest response to the 1.0 ppm concentration of DMNB with about a 10% relative decrease in PL after each exposure, which is competitive when comparing to a previously reported carbazole-based polymer (maximum relative decrease of 20% for equilibrium vapors (≈3 ppm) using a commercial FIDO instrument) and dendrimer (around 4% with vapor concentration in the range 1.0–1.5 ppm) sensing materials.…”

“…The dendritic side chains differ in their steric bulk, conjugation length of the chromophore, and number of branching points. Carbazole moieties were chosen to be part of the chromophore as they have been previously shown to be effective for the detection of nitro-based explosives − and, in some cases, with high sensitivity for the more difficult to detect nitro-containing taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB). , We describe the synthesis, physical, electronic, and photophysical properties of the materials and compare the solid state sensing performance of the polymers with their respective monomers.…”

Dendrimer Enhanced Fingerprint and Explosive Detection: A Critical Review

“…Fibres, flexible films, adhesives, resistant paints, etc., are wellknown polymers. [1][2][3][4][5][6] Polymer chemistry is historically targeted at linear and branching polymers. [7][8][9] In 1978, Fritz Vogtle proposed a divergent synthesis approach that resulted in the first "Cascade molecule.…”

The effect of the phenylene linkage in poly(fluorene-alt-phenylene)s on the thermodynamics and kinetics of nitroaromatic and nitroaliphatic sensing

“…Fluorescence quenching can be achieved using fluorescent small molecules [10,11], dendrimers [9,[16][17][18][19], quantum dots [20], metalorganic frameworks [21] and polymers [6][7][8]12,13]. Polymeric materials has driven this area of research because of the amplification of fluorescence quenching that occurs through the influence of one quencher within the entire multi-fluorophore polymeric chain [6,7].…”

“…Iptycene containing poly(phenylene-ethynylene)s are one of the leading materials used for explosives detection because of their appropriate electron affinity, allowing efficient photoinduced electron transfer, and low packing density, allowing penetration of the analyte [22]. Although these classes of polymers demonstrate high sensitivity towards nitroaromatic compounds, they are limited in terms of nitroaliphatic analytes which are used as taggants or accelerants [18,23]. To address this, polymers based on fluorene-alt-phenylene have had promising quenching properties for nitroaliphatic compounds.…”