Ground and excited state proton transfer of some carbazole derivatives: a linear correlation between the acidity constant and charge density on the deprotonation centre

Abstract

The acidity constants of carbazole (CZ), 2-nitrocarbazole (NC), 2-methoxycarbazole (MOC) and 3-methylcarbazole (MC) have been determined in the ground as well as in the lowest excited singlet state. The excited state acidity constant (pK∗) has been estimated following Weller's fluorometric titration technique and the ground state acidity constant (pK) has been determined therefrom using the Förster cycle principle. Semi-empirical calculations (AM1-SCI) have been performed to calculate the charge density on the deprotonation centre (>N-) for the different probes. A good linear correlation exists between the acidity constants and the charge densities on the deprotonation centres in the respective electronic states.