Pressure-induced charge transfer in phthalocyanine conductors

Pressure dependence of optical absorption spectra were measured for NiPc(AsF6)0.5 and CoPc(AsF6)0.5. The absorption spectra of these compounds show a reversible and systematic change in the infrared, near-infrared, and visible regions. We interpreted this change that the d-electrons of the metal ion of MPc began to transfer to the macrocycle at 0.5 GPa in NiPc(AsF6)0.5 and 1.1 GPa in CoPc(AsF6)0.5 and that this electron transfer continued up to about 7 GPa. The analysis of the plasmon absorption suggests that a metal-nonmetal transition occurs in NiPc(AsF6)0.5 accordingly as the d-electrons are filled into the π-conduction band.