Solvatochromism and proton transfer kinetics of 1,5- and 1,7-naphthalenediols in the excited singlet state: A study by electronic spectra

Abstract

A study of solvent and <i>p</i>H effects on absorption and fluorescence of 1,7- and 1,5-naphthalenediols has been carried out. The life-times of neutral and monoanionic forms of both naphthalenediols have been determined. Solvatochromic shift of 1,7-naphthalenediol (l,7ND) is different from that of 1,5-naphthalenediol (1,5ND) both in the ground and excited states. The difference is more in S₁ state. In 1,5ND the -OH groups are α αʹ and placed symmetrically, but in 1,7ND the –OH groups are α, βʹ and their positions are not symmetrical. The large solvatochromic and Stoke's shifts are explained on the basis of the point group symmetry of naphthalenediols. The stretched sigmoidal fluorimetric titration curves obtained for the equilibrium between neutral form and monoanion of both NDs are analysed using Weller's steady state kinetics and lifetimes of the species. These curves meet only at the ground state <i>pK</i>_a<i> </i>values. The excited state equilibrium constants determined from rate constants and by other methods are compared.