Phthalocyanines based QCM sensors for aromatic hydrocarbons monitoring: Role of metal atoms and substituents on response to toluene

• Phthalocyanines based QCM sensors for toluene vapor detection are reported.
• Unsubstituted phthalocyanines based QCM devices exhibit low sensitivity.
• No effect of change of central metal atom in phthalocyanines on toluene sensitivity is observed.
• Strong effects of peripheral tert-butyl ligand on toluene sensitivity are noted.
• Enhancement in sensitivity of ttb-MPcs based QCM devices result from amorphous and highly porous nature of sensing layers.

The sensing properties of various metallophthalocyanines layered on Quartz Crystal Microbalance (QCM) transducers towards toluene vapor were investigated. Structural and morphological properties of thermally evaporated thin films of substituted and unsubstituted phthalocyanines were firstly characterized by Infrared spectroscopy, X-ray Diffraction and Scanning Electron Microscopy. The sensing characteristics were then determined from QCM responses to toluene at room temperature and correlated to physical and chemical properties of thin films. Effects of molecular composition of phthalocyanine, especially the nature of metal atom in the central cavity and peripheral grafted substituents, on sensor metrological characteristics were established. No significant effect because of change of the central metal atom (Cu, Zn, Fe, Co) in monomeric phthalocyanines was observed on toluene sensitivity. In contrast, strong effects of substituents particularly tert-butyl group at the periphery of the phthalocyanine ring on sensor response were highlighted. The sensing behavior of metallophthalocyanines towards toluene has been interpreted in correlation with the chemical nature of the materials (nature of metal atom and peripheral grafting groups), the physical properties of the sensitive films (structure, morphology and thickness) and the involved molecular interactions forces.

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