Absorption and magnetic circular dichroism spectra of metal-free phthalocyanine in ultraviolet-transparent solvents

Absorption and magnetic circular dichroism spectra of metal-free phthalocyanine (H2Pc) have been recorded over the range 270–800 nm. The use of solvents transparent in the 270–400 nm region allows the observation for the first time of the B band spectral envelope of H2Pc in solution. The mcd spectrum clearly indicates that the complex (NH4)2Pc is formed when ammonia is bubbled through a solution of H2Pc in dimethyl sulphoxide. The multi-transition nature of the B band region is identified as a property of the phthalocyanine π electron system rather than arising from charge transfer between the ring and a central metal cation.