Molecular semiconductors for magnetometry and oximetry: lithium phthalocyanine radical

Lithium phthalocyanine (PcLi) is an intrinsic molecular semiconductor. This radical can crystallize in various crystalline phases, x, α, β, which show different properties (conductivity, magnetism, oxygen sensitivity). The x and β polymorphs may be studied on single crystals. Thin films are obtained by sublimation under vacuum on glass or oriented substrates. These films present different types of organization and crystalline structures depending on the nature of the substrate, its temperature, subsequent heating and solvent treatments, etc. The only x-form shows the following properties: (i) the presence of channels in which the dioxygen molecules can migrate; (ii) a strong overlap between consecutive PcLi molecules in a stack and a very efficient spin diffusion revealed by a very narrow EPR line. The latter is strongly broadened in the presence of oxygen. This chemically stable system is then a very good candidate for magnetometry and oximetry applications, in particular in aggressive environments. Nevertheless, these exceptional properties are not yet observed on x-form thin films.