Exploitation of the Z-scan technique as a method to optically probe pK_a in organic materials: application to porphyrin derivatives

Abstract

We demonstrate the use of the Z-scan technique as a method to measure a chemical parameter, the ${\mathrm{pK}}_{\mathrm{a}}$ 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-N-methyl-pyridyl) porphyrin. The results were compared with linear absorption measurements and electron paramagnetic resonance, the usual techniques employed to determine ${\mathrm{pK}}_{\mathrm{a}}$ values in aqueous solutions, and showed excellent agreement.

© 2000 Optical Society of America