UV–visible spectral study on the stability of lead phthalocyanine complexes

UV–visible electronic spectral study has been done on lead phthalocyanine (PbPc), lead tetranitro phthalocyanine (PbTNP) and lead tetraamino phthalocyanine (PbTAP) in dimethyl sulphoxide (DMSO) and H2SO4 media. Metal free phthalocyanine (H2Pc) is insoluble in DMSO and soluble in conc. H2SO4. The study has been extended to H2Pc to compare the stability of phthalocyanine structure with the PbPc complexes in H2SO4 medium. PbPc complexes are stable in DMSO, and all the complexes are more stable in 36 N H2SO4 than in 30 N and 28 N H2SO4 media. Further, complete demetallation and degradation of the phthalocyanine structure have been observed for all the PbPc complexes in 36 N H2SO4 medium within a week's time. The stability of these complexes is compared with H2Pc in H2SO4 medium. The decomposition reactions in H2SO4 media for H2Pc, PbPc, PbTNP and PbTAP are followed spectrophotometrically and rate constants were calculated. The decomposition reactions were found to follow the first-order kinetics with respect to the concentration of their respective phthalocyanine derivatives.