INTERACTIONS OF NITROGEN-DIOXIDE WITH LANGMUIR-BLODGETT-FILMS OF A COPPER PORPHYRIN

The in-plane d.c. conductivity of Langmuir-Blodgett (LB) monolayers and multilayers of a copper(II) mesoporphyrin IX diol has been studied in the presence of the toxic electron acceptor gas NO2 and other gases. The current increases by up to four orders of magnitude in the presence of 10 ppm NO2. The effects on conductivity of different substrates, deposition conditions, LB film thickness and overlayers are briefly discussed in terms of the physical film structure. The chemical changes in the films on exposure to gas and the conduction mechanism are investigated by studies on reversibility, UV-visible and IR spectral changes, and the temperature dependence of the conductivity. The observations are consistent with a reversible step to give a highly conductive π cation radical followed by irreversible changes of molecular structure on continued exposure. © 1990.