Photoinduced degradation of indigo carmine: insights from a computational investigation
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ORIGINAL PAPER
Photoinduced degradation of indigo carmine: insights from a computational investigation ˜ C. da Silva1 · Fernando Campanha˜ Vicentini2 · Antonio H. da S. Filho1 · Flaviana S. Candeias2 · Sebastiao 2 3 ˆ ˜ · Alex Brown · Gabriel L. C. de Souza1,4 Monica H. M. T. Assumpc¸ao Received: 12 July 2020 / Accepted: 8 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this work, we present a computational investigation on the photoexcitation of indigo carmine (IC). Physical insights regarding IC photoexcitation and photolysis were obtained from a fundamental perspective through quantum chemistry computations. Density functional theory (DFT) was used to investigate the ground state while its time-dependent formalism (TD-DFT) was used for probing excited state properties, such as vertical excitation energies, generalized oscillator strengths (GOS), and structures. All the computations were undertaken using two different approaches: M06-2X/6-311+G(d,p) and CAM-B3LYP/6-311+G(d,p), in water. Results determined using both methods are in systematic agreement. For instance, the first singlet excited state was found at 2.28 eV (with GOS = 0.4730) and 2.19 eV (GOS = 0.4695) at the TDDFT/CAM-B3LYP/6-311+G(d,p) and TD-DFT/M06-2X/6-311+G(d,p) levels of theory, respectively. Excellent agreement was observed between the computed and the corresponding experimental UV-Vis spectra. Moreover, results suggest IC undergoes photodecomposition through excited state chemical reaction rather than via a direct photolysis path. To the best of our knowledge, this work is the first to tackle the photoexcitation, and its potential connections to photodegradation, of IC from a fundamental chemical perspective, being presented with expectations to motivate further studies. Keywords Indigo carmine · Dye degradation · Density functional theory (DFT) · Time-dependent density functional theory (TD-DFT)
Introduction Dyes and pigments have been used by humanity for centuries. For instance, mollusc purple, madder, and This paper belongs to Topical Collection XX-Brazilian Symposium of Theoretical Chemistry (SBQT2019) Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00894-020-04567-2) contains supplementary material, which is available to authorized users. Gabriel L. C. de Souza
[email protected] 1
Departamento de Qu´ımica, Universidade Federal de Mato Grosso, Cuiab´a, Mato Grosso, 78060-900, Brazil
2
Centro de Ciˆencias da Natureza, Universidade Federal de S˜ao Carlos, Buri, S˜ao Paulo, 18290-000, Brazil
3
Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada
4
Department of Chemistry, Washington State University, Pullman, Washington, 99164, USA
indigo/woad were very recently detected in Egyptian textiles of the first millennium from the Fill-Trevisiol collection [1]. However, since a few decades ago, it has been known that dyes generated in wastewaters, especially those resulting from industrial activities, can cause sever
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