The new substituent constants $({sigma}^{ast})$ are calculated from the acidity constants $(pK^{ast})$ of phenol derivatives in the excited state ($^1L_b$). These substituent constant are applied to the Hammett equations and found good correlation with $pK^{ast}$ of 2,6-di-tert-butyl phenol, benzamide, nitroaniline, thiophenol, azobenzene, and benzoic acid derivatives. The correlation was much better than that of ground state substituent constants such as ${sigma},;{sigma}^+$, and ${sigma}^-$. From these results, the new substituent constants $({sigma}^{ast})$are proposed to be used for the linear free energy relationship in the $^1({pi},{pi}^{ast})$ excited states of phenyl compounds.