Ab initio investigation of substituent effects on the excited electronic states of flavylium cation analogues of anthocyanin pigments

Abstract

Anthocyanins are particularly noteworthy natural plant pigments that are responsible for the red, purple and blue color of many fruits, vegetables and flowers. Dietary anthocyanins have potential health benefits, but their color loss due to pH-dependent chemistry limits widespread application as coloring agents in food and consumer products. The ability to predict the color of synthetic analogues of natural pigments is crucial to the rational development of new bioinspired dyes and pigments with tailored colors and properties with lower potential for environmental and health concerns than those of conventional synthetic pigments. In this work, we employ the ab initio second-order algebraic diagrammatic construction, ADC(2), level of theory to calculate the absorption spectra of 26 synthetic flavylium cation analogues of anthocyanins. In general, the theoretical absorption spectra compare favorably with the corresponding experimental absorption spectra in an aqueous solution. The excitation energies, the charge transfer character, and the oscillator strengths of the electronic transitions provide insight into the effects of the type and position of the substituents on the excited singlet and triplet states of these compounds. The results show that the theoretical framework employed constitutes a reliable tool for obtaining a deeper understanding of the properties of bioinspired synthetic analogues of anthocyanin pigments.