We observed pressure effects on the rate of thermal fading of colored chromene 1 photochemically generated from 2 in ionic liquids. The reaction rates were retarded with increasing pressure in [C-4-mim][CS], [bzl-mint][Tf2N], and [mnp-mim][Tf2N], whereas the reaction rate increased with pressures in [C-4-mim][Tf2N]. These pressure-induced retardations, so-called dynamic solvent effects, result from the slow thermal fluctuations of solvents.