Development of lutetium bisphthalocyanine/carbon nanotube Langmuir-Blodgett films: Sensing properties

Abstract

A method has been developed to obtain good quality Langmuir-Blodgett (LB) films of mixtures of lutetium bisphthalocyanine and carbon nanotubes. The π-A isotherms exhibit high monolayer stability and the compressed monolayers are easily transferred to solid substrates by Y-type deposition. The electronic absorption spectra of the composite LB films show the characteristic bands of both compounds; the bands appear broader and shifted to higher wavelengths than those observed in solutions or in disordered films prepared by the casting method. The films are sensitive to oxidant or reducing vapors, whose presence cause modifications in the electronic absorption spectra of the films. These fast and reversible changes can be the basis of optical sensors based on thin films of lutetium bisphthalocyanine and carbon nanotubes. LB film electrodes immersed in KCl and KClO4 solutions show electroactivity associated to the oxidation and reduction of the phthalocyanine ring. Important changes in the UV-vis-NIR spectra registered in situ simultaneously to the application of the electrical potential have been observed. The electrochromism observed opens the possibility of using such thin films in electrochromic devices. Composite films show characteristic electrochemical responses when exposed to solutions of antioxidants, where a certain degree of electrocatalytic effect is observed. The enhanced degree of selectivity can be used in the development of voltammetric sensors.