Magnesiumphthalocyanine (MgPc) is a blue pigment whose X-phase (MgPc/(H2O)2) is known to exhibit an intense near-IR absorption. The effect of water desorption on the dark conductivity and photoconductivity at elevated temperatures has been investigated in evaporated thin films of the X-phase of MgPc. Both dark conductivity and photoconductivity are found to greatly diminish with the onset of water desorption around 150°C. This is due to the scattering of charge carriers at defects formed by collapse of the vacancies of water molecules. Especially, the photoconductivity is quite sensitive to subtle structural changes due to thermal motion of water molecules in the lattice, even before water desorption. It is therefore crucial to keep the water molecules firmly coordinated to the central metal for the stable operation of MgPc-photoreceptors.
J. Mizuguchi, H. Takahashi, K. Shiokawa, "Desorption of Water Molecules and its Effect on the Dark Conductivity and Photoconductivity in X-Magnesiumphthalocyanine" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP19), 2003, pp 693 - 696, https://doi.org/10.2352/ISSN.2169-4451.2003.19.1.art00060_2