Nitroanilines as Quencher of Pyrene and 1-Methyl Pyrene Fluorescence

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

cordoba

Congreso; XI ELAFOT 2012; 2012

Nitroanilines are intermediates in the synthesis of dyes, drugs, pesticides, andherbicides. They have been used as fluorescence quenchers of organic chromophores,biomacromolecules, as well as nanomaterials.[1] In fact, some of these fluorescent systemshave been used as isomeric aromatic amine probes.[2] In addition, the capacity ofnitroanilines as quenchers has been used to study materials, such as fluorescent surfactantaggregates.It has been suggested that, depending on the nature of the fluorophore, its emissionquenching by nitroanilines is static or dynamic, can occur via electron or energy transfer, orcan involve formation of transitory charge-transfer complexes or exciplexes (which decay byelectron transfer, intersystem crossing, or internal conversion). Therefore, a systematic studyon the interaction between a well-known and extensively used fluorophore, such as pyrene,and NAs appeared of interest to gain insight into their role as quenchers. Pyrene has beenwidely used as a probe due to i) its absorption (strength) features, ii) its long singlet lifetime (>100 ns), and the information that can be obtained from its fluorescence emission (I3/I1 ratio)and iii) its long-lived triplet excited state (microsecond scale). This chromophore has beingused in fluorescent chemosensors that can recognize selectively chemical species in potentialanalytical applications [3]. In fact, nitrated explosives have been detected by fluorescencequenching of pyrene and related compounds.[4]We report here on the quenching of pyrene and 1-methylpyrene fluorescence byunsubstituted NAs, methylnitroanilines, and a dinitroaniline in toluene and 1,4-dioxane.Steady-state and time-resolved absorption and fluorescence studies were used to gain insightinto the quenching mechanism and the species involved in this process. These studies showthe tendency of NAs to establish specific interactions with the pyrene singlet excited state and,depending on their structure, to be adjacent to the fluorophore at the ground state, someforming a ground state complex.