Solvent polarity switched by CO2 of 1,8-Diazabicyclo [5.4.0] undec-7-ene (DBU) + alcohol mixture was investigated on the effect of alcohol species and DBU mole fraction. The alcohols used in this work were ethylene glycol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol and 1-octanol. Kamlet - Taft parameter was applied for the evaluation of the solvent polarity of DBU + alcohol mixture treated by CO2. Ultraviolet-visible spectra of a solvatochromic dye N, N-Dimethyl-4-nitroaniline was used for the determination of the Kamlet - Taft parameter. The DBU mixture with ethylene glycol provides the switchable polarity by CO2 larger than those with other alcohol. The switchable polarity of DBU + ethylene glycol and DBU + 1-propanol mixtures increases with the mole fraction of DBU. A molecular information from quantum calculation can provide the modeling of the switchable polarity by CO2. The Kamlet - Taft parameter of DBU + alcohol mixture is estimated from the molecular surface charge density. The estimated Kamlet - Taft parameter of DBU + alcohol mixture represents the experimental data within the absolute deviation 0.1. (C) 2019 Elsevier B.V. All rights reserved.