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Abstract
There is a recognized need in the area of explosives detection for fluorescence-based sensing systems that are capable of not only producing a turn-on response but also generating a distinctive spectral signature for a given analyte. Here, we report several supramolecular ensembles displaying efficient fluorophore displacement that give rise to an increase in fluorescence intensity upon exposure to various nitroaromatic compounds. The synthetic supramolecular constructs in question consist of a tetrathiafulvalene (TTF)-based pyrrolic macrocycle, benzo-TTF-calix[4]pyrrole (Bz-TTF-C4P), and fluorescent dyes, monomeric or dimeric naphthalenediimide (NDI) and perylenediimide (PDI) derivatives, as well as chloride or hexafluorophosphate (PF6-) salts of rhodamine 6G (Rh-6G). In chloroform solution, these assemblies exist in the form of discrete supramolecular complexes or oligomeric aggregates depending on the specific dye combinations in question. Each ensemble was tested as a potential explosive-responsive fluorescence indicator displacement assay (FIDA) by challenging it with a series of di- and trinitroaromatic compounds and examining the change in fluorescence spectral characteristics. Upon addition of nitroaromatic compounds (NACs), either a "turn-on" or a "turn-off" fluorescent response was observed depending on the nature of the constituent fluorophore and, where applicable, the counteranion. The FIDAs based on the PDI derivatives were found to display not only a ratiometric fluorescence enhancement but also analyte-dependent spectral changes when treated with NACs. The NAC-induced fluorescence spectral response of each ensemble was rationalized on the basis of various solution-phase spectroscopic studies, as well as single-crystal X-ray diffraction analyses.

Affiliations

Ji Yoon Lee  1 , Harrison D Root  2 , Rashid Ali  1   3 , Won An  4 , Vincent M Lynch  2 , Steffen Bähring  5 , In Su Kim  4 , Jonathan L Sessler  2 , Jung Su Park  1
1 Department of Chemistry, Sookmyung Women's University, Yongsan-gu, Seoul 04310, Republic of Korea.
2 Department of Chemistry, The University of Texas at Austin, 105 East 24th Street-Stop A5300, Austin, Texas 78712-1224, United States.
3 Department of Chemistry, Jamia Millia Islamia, Jamia Nagar (Okhla), New Delhi 110025, India.
4 School of Pharmacy, Sungkyunkwan University, Suwon 16419, Republic of Korea.
5 Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark.