Theoretical Study on the Color of Chemical Species of Cyanidin Depending on pH

Theoretical studies were conducted using PM3 RHF-CI calculation, a semi-empirical quantum chemical method, to explain the absorption characteristics of cyanidin chemical species, which is a plant pigment substance that changes to pH. Chemical species with resonance structural relationships in a specific pH range showed the same appearance of thermodynamic stability, frontier orbitals and molecular electrostatic potentials. And chemical species in equilibrium relationships showed different propensity. The absorption characteristics of cyanidin at the maximum absorption wavelength were the result of two or more superimposed electronic transitions at pH 3 or less and 8-10, and a single electronic transition from HOMO to LUMO at other pHs. It is believed that the experimental results and methods obtained during the research will be useful as basic data for future research related to cyanidin chemical species.