2-Naphthol-aliphatic amine exciplex systems: A method for approximate estimation of kinetic parameters

The fluorescence quenching behavior of 2-naphthol was studied with aliphatic and alcohol amines (diethylamine, triethylamine, n-propylamine, n-butylamine, ethanolamine, diethanolamine, triethanolamine) as quenchers in solvents of varying polarity (cyclohexane, acetonitrile and methanol). The quenching proceeded via the formation of an emissive exciplex. The equilibrium constant for the formation of the exciplex (KE) in the first excited state was calculated from the fluorescence intensities of the monomer and exciplex intensities. All the rate constants appearing in the kinetic scheme (k1 to k6) for the two state system were then estimated with this equilibrium constant (KE) by using an approximate but essentially steady-state method based on the Ware's mechanism. Variable temperature experiments were carried out to obtain certain thermodynamic parameters like the entropy (ΔSE0), enthalpy (ΔHE0), free energy of formation (ΔGE0) and the formation constant (KE) for the exciplex. The equilibrium constant (KE) calculated from both the methods agreed very well. AM1 calculations were also done to obtain information about the ground and excited geometry of the naphthol-amine complex.