INVESTIGADORES
CORREA Nestor Mariano
artículos
Título:
An Interesting Case where Water Behaves as a Unique Solvent. 4-Aminophthalimide Emission Profile to Monitor Aqueous Environment
Autor/es:
ANDRES DURANTINI; R DARIO FALCONE; JORGE D ANUNZIATA ; ELSA B ABUIN; EDUARDO A LISSI; JUANA J. SILBER; N MARIANO CORREA*
Revista:
JOURNAL OF PHYSICAL CHEMISTRY B
Editorial:
American Chemical Society
Referencias:
Año: 2013 vol. 117 p. 2160 - 2168
ISSN:
1089-5647
Resumen:
The behavior of 4-aminophthalimide (4-AP), a common
molecular probe utilized in solvation dynamics experiments, was revisited in
polar aprotic and protic solvents using absorption, steady-state, and timeresolved
fluorescence (TRES) techniques. Also, the deuterium isotope
effect was investigated using D2O as solvent. The absorption spectra of 4-
AP consist of two absorption bands with maxima around 300 nm (B2 band)
and 370 nm (B1 band) depending on the environment, while the emission
feature consists of a single band. In all the solvents investigated (excluding
water), the 4-AP photophysics is similar and the emission spectra are
independent of the excitation wavelength used. In water the behavior is
unique and the emission spectra maximum is different depending on the
excitation wavelength used. The emission maximum is 561.7 nm using the
excitation wavelength that correspond to the B2 absorption band maximum
(ëexcB2 = 303.4 nm) but is 545.7 nm when the excitation wavelength that correspond to the B1 absorption maximum (ëexcB1 =
370.0 nm) is used. Moreover, while the fluorescence decays of 4-AP in water exhibit no emission wavelength dependence at
ëexcB2, the situation is quite different when ëexcB1 is used. In this case, we found a time-dependent emission spectrum that shifts to
the blue with time. Our results show that the solvent-mediated proton transfer process displays a fundamental role in the 4-AP
emission profile and for the first time a mechanism was proposed that fully explains the 4-AP behavior in every solvent including
water. The deuterium isotope effect confirms the assumption because the proton-transfer process is dramatically retarded in this
solvent. Consequently, we were able to elucidate not only why in water the emission spectra depend on the excitation wavelength
but also why the time-dependent emission spectra shift to the blue with time. Thus, our work reveals the importance that the
medium has on the behavior of a widespread dye used as chromophore. This is significant since the use of chromophores without
understanding its chemistry can induce artifacts into the interpretation of solvation dynamics in heterogeneous environments, in
particular, those provided by aqueous biological systems.