UV Spectral Studies in Protonation of Cu-Phthalocyanine and Phthalocyanine in Sulphuric Acid-Solvent

Abstract

Our studies in protonation of phthalocyanine (H₂Pc) with sulphuric
acid remove the controversy concerning its degree of
protonation. The absorption spectra of phthalocyanine (H₀Pc) and
Cu-phthalocyanine (CuPc) have been used to illustrate the effect of
electronic nature of coordinated metal, its protonation depth and
position of bands in sulphuric acid medium. The CuPc and its ligand
H₂Pc absorb 786 nm and 754 nm respectively in sulphuric acid.
The position of bands of H₂Pc and CuPc in electronic absorption
spectra do not seem to depend upon the sulphuric acid concentration
and remain the same even in 100% H₂SO₄. This obviously indicates
that CuPc and H₂Pc  both yield a single protonated form in sulphuric
acid. The spectral changes during the protonation are almost the
same. This is clear indication of the same type of proton attachment
and the same site of its localization.