title: Fluorescent detection of nitroaromatics and 2,3-dimethyl 2,3-dinitrobutane (DMNB) by a zinc complex: (salophen)Zn.
abstract: Fluorescent sensors for the detection of chemical explosives are in great demand. It is shown herein that the fluorescence of ZnL* (H2L=N,N'-phenylene-bis-(3,5-di-tert-butylsalicylideneimine)) is quenched in solution by nitroaromatics and 2,3-dimethyl-2,3-dinitrobutane (DMNB), chemical signatures of explosives. The relationship between the structure and fluorescence of ZnL is explored, and crystal structures of three forms of ZnL(base), (base=ethanol, tetrahydrofuran, pyridine) are reported, with the base=ethanol structure exhibiting a four-centered hydrogen bonding array. Solution structures are monitored by 1H NMR and molecular weight determination, revealing a dimeric structure in poor donor solvents which converts to a monomeric structure in the presence of good donor solvents or added Lewis bases to form five-coordinate ZnL(base). Fluorescence wavelengths and quantum yields in solution are nearly insensitive to monomer-dimer interconversion, as well as to the identity of the Lewis base; in contrast, the emission wavelength in the solid state varies for different ZnL(base) due to pi-stacking. Nitroaromatics and DMNB are moderately efficient quenchers of ZnL*, with Stern-Volmer constants KSV=2-49 M-1 in acetonitrile solution.
authors.affiliation: Department of Chemistry and Program in Molecular and Cellular Biology, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, USA.
authors.forename: Meaghan E
authors.initials: ME
authors.lastname: Germain
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Vargo
authors.forename: Peter G
authors.initials: PG
authors.lastname: Khalifah
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Knapp
mesh_terms: D002073:Butanes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006860:Hydrogen Bonding; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D017672:Nitrogen Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012459:Salicylates / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D017186:Titrimetry; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D002073:Butanes; D008024:Ligands; D017672:Nitrogen Compounds; D012459:Salicylates; D017967:Zinc Compounds; C090416:salophen; C089312:2,3-dimethyl-2,3-dinitrobutane