Probing the Indigo Molecule in Maya Blue Simulants with Resonance Raman Spectroscopy

Author(s)

Bemardino, N. D. ^[1] ; Constantino, V. R. L. ^[2] ; de Faria, D. L. A. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Chem, Dept Fundamental Chem, Mol Spect Lab, Ave Prof Lineu Prestes 748, BR-05508000 Sao Paulo - Brazil

^[2] Univ Sao Paulo, Inst Chem, Dept Fundamental Chem, Lamellar Solids Lab, Ave Prof Lineu Prestes 748, BR-05508000 Sao Paulo - Brazil

• Document type: Journal article
• Source: Journal of Physical Chemistry C; v. 122, n. 21, p. 11505-11515, MAY 31 2018.
• Web of Science Citations: 3

Abstract

Maya blue (MB) simulants were prepared from mixtures of indigo and palygorskite (ind-paly) and investigated by resonance Raman and UV-vis absorption spectroscopies together with thermogravimetric analysis, aiming to enlarge the understanding of the dye-clay interaction, the relationship between color and chemical stability, and the alleged formation of dehydroindigo (DHI); for comparative purposes, other simulants were prepared using sepiolite, laponite, and montmorillonite. The results obtained here suggest that the greenish hue that develops when the ind-paly is heated seems to be linked with a decrease in the indigo molecular symmetry, which causes an increase in the oscillator strength of an absorption band at 500 nm (forbidden under the C(2)h symmetry) and a bathochromic shift and narrowing of the intense electronic transition at 657 nm (indigo). The DHI characteristic features are not observed in the resonance Raman spectrum (457.9 nm) of the ind-paly system, contrary to what happens with sepiolite, Laponite and montmorillonite that, however, do not present the chemical stability observed for MB. Resonance Raman, UV-vis absorption spectroscopy, and thermal analysis provided firm evidences that in ind-paly, the dye is inside the micropores, interacting through hydrogen bonding with water molecules coordinated with the metal ions of the clay framework. (AU)

• FAPESP's process: 11/50318-1 - Development of compounds with pharmacological or medicinal interest and of systems for their transport, detection and recognition in biological media
• Grantee: Ana Maria da Costa Ferreira
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 12/05643-4 - Impact of nanostructural aspects on the stability of dyes and pigments of archaeological interest
• Grantee: Nathália Delboux Bernardino
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 12/13119-3 - Vibrational spectroscopy in condensed phases
• Grantee: Mauro Carlos Costa Ribeiro
• Support Opportunities: Research Projects - Thematic Grants