Detection of Volatile Organic Compounds Using Porphyrin Derivatives

Seven different porphyrin compounds have been investigated as colorimetric gas sensors for a wide range of volatile organic compounds. The porphyrins examined were the free base and Mg, Sn, Zn, Au, Co, and Mn derivatives of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21<i>H</i>,23<i>H</i>-porphine. Chloroform solutions of these materials were prepared and changes in their absorption spectra induced by exposure to various organic compounds measured. The porphyrins that showed strong responses in solution were selected, and Langmuir−Blodgett films were prepared and exposed to the corresponding analytes. This was done to determine whether they are useful materials for solid state thin film colorimetric vapor sensors. Porphyrins that readily coordinate extra ligands are shown to be suitable materials for colorimetric volatile organic compound detectors. However, porphyrins that already have bound axial ligands when synthesized only show a sensor response to those analytes that can substitute these axial ligands. The Co porphyrin displays a considerably larger response than the other porphyrins investigated which is attributed to a switch between Co(II) and Co(III) resulting in a large spectral change.