The photophysics of salicylic acid derivatives in aqueous solution

Abstract

The photophysics of a number salicylic acid derivatives (SADs) in aqueous solutions was investigated in a wide range of pH by time-correlated single photon counting (λex=350 nm, τresp=300 ps) and fluorescence up-conversion (λex=266 nm, τresp= 300 fs) techniques. The acid-base equilibrium constants in the ground (pK a) and the excited states (pK*a), the fluorescence quantum yields as well as the lifetimes of anionic, neutral, and cationic forms of SADs were determined. Evidence of ultrafast excited-state intramolecular proton transfer (ESIPT) leading to the formation of the proton-transferred excited state of SADs was obtained from the fluorescence up-conversion measurement. The nature of the ESIPT process is discussed. Copyright © 2008 John Wiley & Sons, Ltd.