Nitroanilines as Quenchers of Pyrene Fluorescence

CARLOS AGUDELO-MORALES; OSCAR FERNANDO SILVA; RAQUEL E. GALIAN; JULIA PÉREZ-PRIETO

Chemphyschem

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2012 vol. 13 p. 4195 - 4201

1439-4235

The quenching of pyrene and 1-methylpyrene fluorescence bynitroanilines (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 ofthe 4-NAs as quenchers and fit with a sphere-of-action model.This suggests a 4-NA tendency of being in close proximity tothe fluorophore, which could be connected with their high polarity/hyperpolarizability. In addition, emission and excitationspectra evidence the formation of emissive pyrene?NAground-state complexes in the case of the 4-NAs and, ina minor degree, in the 2-NA. Moreover, time-resolved fluorescenceexperiments show that increasing amounts of NA decreasethe pyrene fluorescence lifetime to a degree that dependson 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?dipoleenergy transfer from the pyrene singlet excited state (1Py) tothe NAs; this could be due to the low NA concentration usedin these experiments. Transient absorption spectra show thatthe formation of the pyrene triplet excited state (3Py) is barelyaffected by the presence of the NAs in spite of their efficiencyin 1Py quenching, suggesting the involvement of 1Py?NA exciplexeswhich?after intersystem crossing?decay efficientlyinto 3Py.