Nitroanilines as quenchers of pyrene fluorescence.

Chemphyschem : a European journal of chemical physics and physical chemistry (2012-10-24)
Carlos E Agudelo-Morales, Oscar F Silva, Raquel E Galian, Julia Pérez-Prieto
ABSTRACT

The quenching of pyrene and 1-methylpyrene fluorescence by nitroanilines (NAs), such as 2-, 3-, and 4-nitroaniline (2-NA, 3-NA, and 4-NA, respectively), 4-methyl-3-nitroaniline (4-M-3-NA), 2-methyl-4-nitroaniline (2-M-4-NA), and 4-methyl-3,5-dinitroaniline (4-M-3,5-DNA), are studied in toluene and 1,4-dioxane. Steady-state fluorescence data show the higher efficiency of the 4-NAs as quenchers and fit with a sphere-of-action model. This suggests a 4-NA tendency of being in close proximity to the fluorophore, which could be connected with their high polarity/hyperpolarizability. In addition, emission and excitation spectra evidence the formation of emissive pyrene-NA ground-state complexes in the case of the 4-NAs and, in a minor degree, in the 2-NA. Moreover, time-resolved fluorescence experiments show that increasing amounts of NA decrease the pyrene fluorescence lifetime to a degree that depends on the NA nature and is larger in the less viscous solvent (toluene). Although the NA absorption and the pyrene (Py) emission overlap, we found no evidence of dipole-dipole energy transfer from the pyrene singlet excited state ((1)Py) to the NAs; this could be due to the low NA concentration used in these experiments. Transient absorption spectra show that the formation of the pyrene triplet excited state ((3)Py) is barely affected by the presence of the NAs in spite of their efficiency in (1)Py quenching, suggesting the involvement of (1)Py-NA exciplexes which--after intersystem crossing--decay efficiently into (3)Py.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
1,4-Dioxane, anhydrous, 99.8%
Sigma-Aldrich
1,4-Dioxane, ACS reagent, ≥99.0%
Sigma-Aldrich
1,4-Dioxane, suitable for HPLC, ≥99.5%
Supelco
1,4-Dioxane, analytical standard
Sigma-Aldrich
1,4-Dioxane, ReagentPlus®, ≥99%
Supelco
1,4-Dioxane solution, certified reference material, 2000 μg/mL in methanol, ampule of 1 mL
Sigma-Aldrich
1,4-Dioxane, puriss. p.a., ACS reagent, reag. ISO, reag. Ph. Eur., ≥99.5% (GC)
Sigma-Aldrich
1,4-Dioxane, ACS reagent, ≥99.0%
Sigma-Aldrich
1-Methylpyrene, suitable for fluorescence, ≥97.0% (GC)
Sigma-Aldrich
1,4-Dioxane solution, NMR reference standard, 40% in benzene-d6 (99.6 atom % D)
Sigma-Aldrich
1,4-Dioxane solution, NMR reference standard, 40% in benzene-d6 (99.6 atom % D), chromium(III) acetylacetonate 5 mg/mL, NMR tube size 5 mm × 8 in.
Sigma-Aldrich
1,4-Dioxane solution, NMR reference standard, 10 mM in D2O ("100%", 99.96 atom % D), NMR tube size 5 mm × 7 in.
Supelco
1,4-Dioxane solution, NMR reference standard, 40% in benzene-d6 (99.6 atom % D), NMR tube size 5 mm × 8 in.
Sigma-Aldrich
1,4-Dioxane solution, NMR reference standard, 40% in benzene-d6 (99.6 atom % D), NMR tube size 10 mm × 8 in.
Supelco
1,4-Dioxane solution, NMR reference standard, 5 mM in chloroform-d (99.8 atom % D), NMR tube size 3 mm × 8 in.
Supelco
1,4-Dioxane solution, NMR reference standard, 5 mM in benzene-d6 (99.6 atom % D), NMR tube size 3 mm × 8 in.
Sigma-Aldrich
1,4-Dioxane solution, NMR reference standard, 40% in benzene-d6 (99.6 atom % D), chromium(III) acetylacetonate 5 mg/mL, NMR tube size 3 mm × 8 in.
Supelco
1,4-Dioxane solution, NMR reference standard, 40% in benzene-d6 (99.6 atom % D), NMR tube size 3 mm × 8 in.