Laser ablation time-of-flight mass spectral studies of metal-substituted phthalocyanines

We have obtained time-of-flight mass spectra for metal complexes of tetrakis(cumylphenoxy)-phthalocyanines, MPc(CP)₄, by pulsed laser ablation from frozen benzene solutions. The Pc complexes themselves act as chromophores for the 355 and 580 nm excitation wavelengths used. Prior vapor pressure osmometry (VPO) and UV/visible absorption studies indicate an increasing degree of molecular association in solution in the order Pb < Cu < Ni < Pd < Hg. The mass spectra of all but the Hg-containing sample are dominated by the monomeric molecular ion (ML⁺) peak. The HgPc(CP)₄ sample shows a pattern containing strong peaks due to HgL₂⁺, Hg₂L₃⁺, Hg₃L₄⁺, and other complex molecular ions. We suggest that this is consistent with formation of a cofacial Hg-linked polymer or oligomer in solution, as proposed in a previous VPO and UV/visible spectroscopy study.