Conjugated Poly(fluorene-quinoxaline) for Fluorescence Imaging and Chemical Detection of Nerve Agents with Its Paper-Based Strip

Abstract

Conjugated polymer of poly(fluorene-co-quinoxaline) was synthesized via Suzuki coupling polymerization. The emission color of the polymer can be tuned depending on the concentration of the polymer in solution. A low-energy bandgap is observed both in the concentrated solution and in the solid state, caused by aggregation of the polymer chains, resulting in long wavelength emission from the quinoxaline moiety, while short wavelength emission can be seen in diluted, well-dissolved solution. The presence of quinoxaline units enables us to demonstrate fluorescence switching and imaging. Paper-based strips containing the polymer are prepared via simple immersion of filter paper in the polymer solution for practical use in the detection of nerve agents. The emission of the paper-based strip is quenched upon exposure to diethyl chlorophosphate (DCP), a nerve agent simulant, and the initial emission intensity can be almost restored by treatment with aqueous sodium hydroxide solution, making a possible reversible paper-based sensor.

Synthesis and Sensing Applications of Fluorescent 3-Cinnamoyl Coumarins

“…This may be due to the electron donating effect of methoxy group which enriched the nucleophilic attack of compound on phosphorous atom of DCP. The Ksv values for both compounds 7 and 8 were found to be higher than the value reported for the DCP sensor based on poly(fluorene-quinoxaline) [ 34 ]. To confirm if the fluorescence quenching is a selective phenomenon for the cinnamoylcoumarins 7 and 8 , we have synthesized three structural analogues (11−13) of compounds 7 and 8 ( Scheme 2 ).…”

Challenges in Fluorescence Detection of Chemical Warfare Agent Vapors Using Solid‐State Films

“…Materials with nitrogen‐based nucleophiles constitute an important class of fluorescent sensors investigated for the detection of nerve agent and simulant vapors. N‐based chemosensors ( Figure ) include quinoline (e.g., 2 ), pyridine (e.g., 3 and 4 ), Schiff bases (e.g., 5 ), amines (e.g., 6 ), or quinoxaline . Solid‐state detection of the nerve agents has been reported to be achievable in different formats including drop‐casting ( 2 ) in a poly(ethylene oxide) (PEO) matrix, having ( 6 ) and ( 4 ) sorbed onto microbeads or glass, or filter paper, respectively, or in the form of a neat thin film by spin‐coating ( 3 ) or ( 5 ) onto quartz substrates.…”

“…Both the mechanisms lead to a fluorescence “turn on” response . There are other N‐based sensing materials (not listed here) that give fluorescence “turn off” signals, but the sensing mechanisms are unclear . Although N‐based chemosensors 3 – 5 have been reported to achieve a very low limit of detection against DCP vapor, false positives from acids due to the protonation of N‐based functionality is likely to be a major issue.…”

Conjugated Copolymers through Electrospinning Synthetic Strategies and Their Versatile Applications in Sensing Environmental Toxicants, pH, Temperature, and Humidity

“…with good sensitivity and selectivity without any considerable interference or contamination of the analyte. The sensors output can be monitored with optical responses, such as fluorescent off-on, on-off, and color changes, or by other coupled electrical read out devices [17][18][19].…”