Solvatochromic data have been collected from the literature or newly measured for 83 molecular solvents, 18 switchable solvents, and 187 ionic liquids that have been cited in the green chemistry literature. The data include the normalized Reichardt's parameter (E^N_T), the Nile red λ_max, and the Kamlet–Taft parameters (α, β, and π*). Disagreements within the literature about the properties of glycerol and poly(ethylene glycol) have been resolved with new data. The switching of a switchable-polarity solvent (also known as a reversible ionic liquid) by CO₂ causes a significant increase in polarity/polarizability (π*) but no change in the basicity (β). A switchable-hydrophilicity solvent undergoes an even greater change in polarity because it merges with an aqueous phase upon exposure to CO₂. Trends observed from the data of ionic liquids are presented, along with concerns about the best method for determining the Kamlet–Taft parameters.