Electrochemical Preparation and EPR Studies of Lithium Phthalocyanine: Evaluation of the Nucleation and Growth Mechanism and Evidence for Potential-Dependent Phase Formation

A very reliable and reproducible electrochemical preparative procedure to obtain oxygen-sensitive lithium phthalocyanine (LiPc) microcrystalline powder, a critical material for in vivo application of electron paramagnetic resonance (EPR) oximetry to measure the partial pressure of molecular oxygen pO2, is described. Important issues including the effect of preparative conditions on the resulting material and the influence of the deposition mechanism on crystal structure are investigated using cyclic voltammetry, chronoamperometry, X-ray diffraction (XRD), and high- and low-frequency EPR measurements. The electrochemical measurements reveal that electrodeposition of LiPc follows a nucleation pathway. Detailed electrocrystallization studies show that the nucleation mechanism is instantaneous and the three-dimensional growth is controlled by the diffusion of the reactant from the bulk solution. Critical evidence, for deposition potential-dependent electrochemical phase formation, is presented. The XRD studie...