Optochemical properties of gas-phase protonated tetraphenylporphyrin investigated using an optical waveguide NH3 sensor

Abstract

5,10,15,20-Tetraphenylporphyrin (TPP) was synthesized, and a glass optical waveguide (OWG, which restricts and maintains the light energy in a specific, narrow space and propagates along the space axially) was coated with a gas-phase protonated TPP thin film to develop a sensor for NH₃ gas detection. The results show that the TPP thin film agglomerated into H-based J-type aggregates after H₂S gas exposure. The molecules in the protonated TPP film OWG sensor acted as NH₃ receptors because the gas-phase protonated TPP film morphologically changed from J-type aggregates into free-base monomers when it was deprotonated by NH₃ exposure. In this case, H₂S gas could be used to increase the relative amount of J-type aggregates in the TPP film and restore the sensor response. The reversible surface morphology of the TPP film was analyzed by ¹H NMR spectroscopy, atomic force microscopy, and UV-vis spectroscopy.