Rational design of dual-state emission fluorophores for sensing nitro explosives by using sulfone unit as an electron acceptor in D-A system.

Dual-state emission (DSE) fluorescent molecules have become the preferred type in designing sensing fluorescent molecules due to the virtue of their bright emission in both solid and liquid states. In this study, five D-A molecules were successfully designed and synthesized according to the design concept that structural modification of D-A molecules can lead to DSE molecules. Among them, the balance between the electron donor with a strong electron donation capacity and the twisted conformation in the whole molecule makes the compounds 3c-3e DSE molecules with excellent optical performances, showing significant solvatochromic effects and large Stoke shifts. In addition, the feasibility of the sulfone unit as an electron acceptor in the D-A structure is also verified, extending the application of sulfone group in the field of fluorescence. Interestingly, the fluorescence of 3c can exhibit sensitive and selective quenching of nitro aromatic compounds (NACs) under the synergistic mechanism of fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET), with LOD as low as 10-8 M and KSV as high as 104 M-1. Furthermore, the selective, efficient, and sensitive detection of NACs by DSE fluorescent molecule 3c in real aqueous samples and loaded on test strips has demonstrated the potential of its practical applications.