Efficient blue-emitting silafluorene-fluorene-conjugated copolymers:selective turn-off/turn-on detection of explosives

摘要

The synthesis and spectroscopic characterization of a series of new blue-emitting silafluorene-fluorene copolymers is described.The polymers are synthesized using kinetically controlled hydrosilylation copolymerization of 1,1-dihydridosilafluorene with a series of 9-substituted 2,7-diethynylfluorenes.The polymers contain a trans-only framework with molecular weights in the range of 13 000-20 000,as determined by gel permeation chromatography(GPC)using polystyrene standards,and by ~1H NMR spectroscopy using dimethylphenylsilane as an end-capping marker group.The three stereoregular polymers synthesized include a 9,9-dihydridofluorene(PSF1),a 9,9-dimethyl-9H-fluorene(PSF2),and a 9,9'-spirobifluorene(PSF3)comonomer with the frameworks.These fiuorenyl units are conjugated through the silicon center of the silafluorene moiety by bridging vinylene groups.Quantum yields of fluorescence range from 20 to 100% with PSF3 having the highest quantum efficiency.Polymers PSF1-3 emit in the blue region of the spectrum(~475 nm),showing good color purity with little change in luminescence properties between the solution and solid-state phases.The polymers were tested for explosives detection properties by a fluorescence-quenching mechanism.Targeted explosives include laboratory prepared TNT,DNT,picric acid,RDX,HMX,PETN,TNG,and Tetryl,as well as production line PETN and C-4.All three polymers exhibit detection of explosive particulates with limits as low as 1 pg cm~(-2)for Tetryl.Polymer PSF1 simultaneously acts as a selective fluorescence"turn-on"sensor for nitrate ester explosives when irradiated with UV light.In the presence of nitrate ester-based explosives such as PETN,PSF1 initially exhibits fluorescence quenching,but continued exposure to UV-light(302 nm),promotes a photochemical reaction forming a luminescent green fluorenone copolymer.This is the first example of a single material acting as both a turn-off and turn-on selective fluorescent sensor for an explosive material.