Pressure-induced d–π charge transfer in one-dimensional phthalocyanine conductors, NiPc(AsF6)0.5 and CoPc(AsF6)0.5

Pressure dependence of optical absorption spectra were measured for (phthalocyaninato)-nickel hexafluoroarsenate, NiPc(AsF6)0.5 and (phthalocyaninato)-cobalt hexafluororarsenate, CoPc(AsF6)0.5. We found a charge transfer from the central metal ion to the macrocycle at 0.5 GPa in NiPc(AsF6)0.5 and 1.1 GPa in CoPc(AsF6)0.5. According to the electron-filling process in the π-conduction band, a metal–insulator transition and an evolution of the energy gap was observed in NiPc(AsF6)0.5. On the other hand, nonmetallic CoPc(AsF6)0.5 showed a continuous change.