Micelle-Induced VersatileSensing Behavior of Bispyrene-BasedFluorescent Molecular Sensor for Picric Acid and PYX Explosives.

Theeffect of surfactant micelles on the photophysical propertiesof a cationic bispyrene fluorophore, Py-diIM-Py, was systemicallyexamined. The results from series of measurements including UV–visabsorption, steady-state fluorescence emission, quantum yield, fluorescencelifetime, and time-resolved emission spectra reveal that the cationicfluorophore is only encapsulated by the anionic sodium dodecyl sulfate(SDS) surfactant micelles and not incorporated in the cationic dodecyltrimethylammoniumbromide (DTAB) and neutral Triton X-100 (TX100) surfactant micelles.This different fluorophore location in the micellar solutions significantlyinfluences its sensing behavior to various explosives. Fluorescencequenching studies reveal that the simple variation of micellar systemsleads to significant changes in the sensitivity and selectivity ofthe fluorescent sensor to explosives. The sensor exhibits an on–offresponse to multiple explosives with the highest sensitivity to picricacid (PA) in the anionic SDS micelles. In the cationic DTAB micelles,it displays the highest on–off responses to PYX. Both the sensitivityand selectivity to PYX in the cationic micelles are enhanced comparedwith that to PA in the anionic micelles. However, the poor encapsulationin the neutral surfactant TX100 micelles leads to fluorescence instabilityof the fluorophore and fails to function as a sensor system. Time-resolvedfluorescence decays in the presence of explosives reveal that thequenching mechanism of two micellar sensor systems to explosives isstatic in nature. The present work demonstrates that the electrostaticinteraction between the cationic fluorophore and differently chargedmicelles plays a determinative role in adjusting its distributionin micellar solutions, which further influences the sensing behaviorof the obtained micellar sensor systems. [ABSTRACT FROM AUTHOR]