A DFT investigation of anthocyanidins

A theoretical analysis of anthocyanidins, a class of natural plant pigments, has been conducted using density functional theory at the B3LYP/6-31G(d) level. It is found that these compounds are non-planar, with the 2-phenyl ring twisted relative to the benzopyrylium rings. TD-DFT calculations reveal a first excited state dominated by two orbital transitions, including the HOMO-LUMO transition. From a comparison of these molecular orbitals with those of related compounds, and from the known chemistry of these compounds, it is suggested that anthocyanidins should be regarded as natural, stable carbocations.