A colorimetric array of metalloporphyrin derivatives for the detection of volatile organic compounds

Spin-coated layers of two metalloporphyrin derivatives (2-nitro-5,10,15,20-tetraphenylporphyrinato) zinc (II) (ZnTPP–NO2) and (2,3-dioxo-5,10,15,20-tetraphenylporphyrinato) zinc (II) (ZnTPPO) have been used as sensing materials for the detection of volatile organic compounds (VOCs) in the UV–vis spectral range. An optical characterization in controlled atmosphere has been carried out by acquiring the absorption spectra of the two metalloporphyrin derivatives both in dry air and in the presence of different VOCs. The results of the optical VOCs sensing tests show interesting differentiation in the optical responses depending on the metal ion and the peripheral substituent of the macromolecules. A 2 × 1 colorimetric array detection of VOCs has been achieved using ZnTPP–NO2 and ZnTPPO as immobilized on a reverse phase silica gel. The gas molecules were detected by the colorimetric array and the obtained responsive images were decomposed to RGB color components using a CMOS image sensor. RGB color components change patterns obtained from the colorimetric array give a good identification of VOCs. Morphological characterization of the sensing layer was also performed by scanning electron microscopy.