Physical insight into the gas-sensing properties of copper (II) tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin Langmuir-Blodgett films

The Langmuir isotherm of copper (II) tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin [CuPaz(t-Bu)₄] has been investigated at the air-water interface. The Langmuir monolayer displays two phase regions, which have a phase transition at 7 mN/m. Langmuir-Blodgett (LB) films have been fabricated onto glass slides, interdigitated electrodes and quartz crystal microbalance electrodes, and characterized by UV-VIS spectroscopy, electrical and nanogravimetric measurements, respectively. The CuPaz(t-Bu)₄ LB films were used to quantity some of the volatile gases, i.e. vapors of hexane, benzene and toluene. UV-VIS spectroscopic measurements reveal that there is an interaction between CuPaz(t-Bu)₄ molecules and the above organic solvent molecules, which is manifested by a red shift and broadening of Soret and Q bands. The response and recovery behaviors, sensitivity and selectivity of the LB films to different organic vapors have been investigated by means of nanogravimetric measurements. Such results offer a potential application of such a porphyrin derivative for the detection of aromatic compounds, even at room temperature.