Impedance spectroscopic investigations of ITO modified by new Azo-calix[4]arene immobilised into electroconducting polymer (MEHPPV)

A sensing material based on calix[4]arene molecules (Azo-C[4]) dispersed in a conjugated polymer (MEHPPV) is deposited by spin coating onto a transparent conducting substrate (ITO) to fabricate new chemical sensors. The electrochemical properties of the sensor are investigated by impedance spectroscopy. Transfer and ion diffusion processes of metal cations (Cu2+, Eu3+) in the Azo-C[4]-MEHPPV membranes are studied. The calixarene molecule behaviour into the polymer membranes is characterised by impedance spectroscopy showing the cation complexation by both, Azo-calix[4]arene and MEHPPV, components of the membrane. The differences in selectivity are found to be represented by variations in the bulk resistance of the membrane (Rm) and in the charge transfer resistance (Rtc) of the interface. The impedance behaviour of the Azo-C[4]-MEHPPV electrodes is modelled by an equivalent electrical circuit. Optical excitation tests of these membranes show that the sensing activity of the calixarene molecules entrapped in the polymer matrix is preserved.