Solvent Effects on Dye Sensitizers Derived from Anthocyanidins for Applications in Photocatalysis

Abstract

Anthocyanidins under the effects of solvents water, ethanol, n-hexane, and methanol are interesting due to their suitability as natural dyes for photocatalytic applications. In this chapter, DFT and TDDFT methodologies are used to study their electronic structure. The results displayed include HOMO, LUMO, HOMO-LUMO gap, chemical properties, and reorganization energies for the ground states, and excited state data are also displayed. Malvidin in gas phase has lower gap energy. After addition of solvents, gap energy increases in all cases but malvidin with n-hexane presents narrower gap. Conceptual DFT results show that cyanidin and malvidin may have good charge transfer. Cyanidin presented lower electron reorganization energy (λ e) using solvent water; however, ethanol and methanol had similar values. TDDFT is used to calculate excited states, and absorption data show wavelength main peak between 479.1 and 536.4 nm. UV-Vis absorption spectra were generated and solvent effects on each molecule is discussed. Anthocyanidins work well in the visible region with the stronger peak at the green region. These pigments are good options for photocatalysis application and cyanidin and malvidin, in this order, may be the best choices for dye sensitization applications.

Excited States of Six Anthocyanidin Variants with Different Solvents as Dye Sensitizers for Photocatalysis

“…The lowest energy absorption in these molecules is due to the transition from HOMO to LUMO with the largest oscillator strength resulting in an enhanced LHE, this approach emphasizes the parameters recommended in the literature to identify the best choice [41,47,48]. Cyanidin, malvidin, and peonidin data has been regenerated for this work with very similar results, considering there is a set of our own results obtained with different methodology that were published previously elsewhere [22]. *Experimental data from the literature [43].…”

“…The difference between HOMO-LUMO is generally accepted as a similar value to the band gap. Results for HOMO-LUMO gap were between 2.539 and 2.881 eV in the *Data regenerated by our research group with a similar theoretical method reported elsewhere [22].…”

“…Such energy was calculated using intramolecular reorganization energies. Molecular orbitals for selected anthocyanidins cyanidin [22], delphinidin, malvidin [22], pelargonidin, peonidin [22], and petunidin corresponding to (a) gas phase, (b) water solvent, (c) ethanol solvent, (d) n-hexane solvent and (c) methanol solvent. H-L gap energy units are in eV.…”

“…Cyanidin lower hole reorganization energy (λ h ) was obtained when used solvent methanol followed by water with similar values but not as close as in the case of λ e . Molecular orbitals charge distribution using B3LYP/6-311 + g(d,p), corresponding to: (a) cyanidin [22], (b) delphinidin, (c) malvidin [22], (d) pelargonidin, (e) peonidin [22] and (f) petunidin.…”

“…Hydroxyl and methoxy groups differentiate these molecules by the number and position of their B-ring [19][20][21]. Prior work related to anthocyanidins by our research group has been published elsewhere and includes cyanidin, malvidin, and peonidin [22]. The methodology from such work was reproduced with an upgraded version of the Gaussian program as part of the continuity work by our research group and we developed further work with additional pigments and calculations which were included in the present work.…”