Highly transparent low-symmetry zinc phthalocyanine-based monolayers for NO₂ gas detection

We demonstrate the NO₂ sensing properties of transparent two-dimensional organic films based on a low-symmetry zinc phthalocyanine (Pc) complexes. The amphiphilic nature of the Pc results in oriented monolayers on substrates, which provide an excellent conformation for Zn-NO₂ interactions without strong Pc intermolecular aggregation. Using the Langmuir-Blodgett technique, we form single monolayer films on glass and show their potential for NO₂ gas detection. We succeed in detecting 100 ppm NO₂, 20 s after gas exposure. We also demonstrate total recovery of the sensing effect by simply heating up to 60 °C. By exhibiting high transparency (~ 97%) and thermal stability, together with low costs and simplicity in scaling the technology for large-area structures, the low-symmetry zinc Pc complexes appear to be highly promising materials for gas sensing applications.