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

摘要

We demonstrate the use of the Z-scan technique as a method to measure a chemical parameter, the pK_(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 pK_(a) values in aqueous solutions, and showed excellent agreement.