Protolytic dissociation of cyanophenols in ground and excited states in alcohol and water solutions

► We studied the protolytic dissociation of 3,4-dicyanophenol and o-, m- and p-cyanophenol in ground and excited electronic states in alcohols. ► The acidic dissociation constant of 3,4-dicyanophenol in the ground state in water was calculated. ► The change of acidity constants in the excited state in comparison to the ground state for all investigated compounds in alcohol and water solutions was obtained. ► 3,4-Dicyanophenol is a stronger acid in ground state in comparison to ortho-, meta- and p-cyanophenol. ► In the excited state the acidity of investigated cyanophenols in methanol strongly increases: the change of pKa is ∼−8.5 for dicyano- and about −7 for o- and m-derivatives.