The SERS spectrum of 1,2-diaminoanthraquinone studied on silver colloid

1,2-Diaminoanthraquinone (1,2-DAAQ) was recently shown to recognize several anions selectively. In the presence of fluoride, it gives origin to a strongly coloured solution, as a consequence of a strong absorption band at ca. 550 nm. The detailed nature of such interaction is not known, although there are evidences for the formation of a hydrogen bonding involving the anion and the amino moieties. In particular, the use of resonance Raman spectroscopy, that would be one of techniques of choice for unveiling the nature of the chromophoric moiety responsible for the coloured solutions of 1,2-DAAQ with anions, is precluded by the intense fluorescence over the visible region. In the present work the SERS technique using silver colloid was employed to overcome such difficulties, besides aiming to reveal the interaction site of 1,2-DAAQ with the surface of the silver colloidal particles. In this work it was possible to determine that the site of the 1,2-DAAQ/FK interaction is one of the amino moieties of the molecule. Such interaction involves a hydrogen bonding of moderate strength. As a consequence of such interaction, the CT transition involving the amino moiety and the p system of 1,2-DAAQ is shifted to lower energies. In the presence of 1,2-DAAQ it appears two new bands at ca. 530 and 405 nm in the silver colloidal solution, assigned to silver aggregates of different sizes. Excitation of the SERS spectra at several wavelengths show that depending on the closeness of the excitation to the CT transition of 1,2-DAAQ, the RR contribution to the SERS enhancement can be significant. The outstanding solvatochromic behavior of 1,2-DAAQ, as shown by its UV–Vis spectra in several solvents, is not reflected in the SERS spectra at two different solvents (dichloromethane and acetonitrile) that show slight differences both in frequency values and relative intensities. q 2004 Elsevier B.V. All rights reserved.