We demonstrate the use of the Z-scan technique as a method to measure a chemical parameter, the pK<sub>a</sub> value, that characterizes the equilibrium constant in acid–base reactions. The measurements were performed with picosecond pulses at 532 nm in Fe(III)-meso-tetrakis(4-<i>N</i>-methyl-pyridyl) porphyrin. The results were compared with linear absorption measurements and electron paramagnetic resonance, the usual techniques employed to determine pK<sub>a</sub> values in aqueous solutions, and showed excellent agreement.
© 2000 Optical Society of America
A. G. Bezerra, Jr., I. E. Borissevitch, A. S. L. Gomes, and Cid B. de Araújo, "Exploitation of the Z-scan technique as a method to optically probe pKa in organic materials: application to porphyrin derivatives," Opt. Lett. 25, 323-325 (2000)