Raman spectroscopy of phthalocyanines and their sulfonated derivatives

The aggregation and photochemistry of the copper (II) 3, 4″, 4″, 4‴-tetrasulfonated phthalocyanine, free base phthalocyanine and copper (II) phthalocyanine have been studied by UV-VIS absorption spectroscopy and resonance Raman spectroscopy (RRS). The vibrational mode ν3 of (Cu(tsPc)4− has been used as a probe in RRS measurements. The photochemistry of monomers and dimers of (Cu(tsPc)4− has been studied in liquid solutions of H2O and DMSO as well as in frozen matrices. Low temperature Raman measurements in a broad temperature range have been carried out for free base phthalocyanine and copper (II) phthalocyanine in DMSO to identify the nature of emissive bands observed in the Raman spectra. It has been shown that the dimerization equilibrium constant K for tetrasulfonated phthalocyanine Cu(tsPc)4− is strongly shifted towards monomeric form in DMSO solutions and in human blood compared to aqueous systems. The emission band at around 682 nm in DMSO and aqueous solutions observed at 77 K for tetrasulfonated salt of copper(II) phthalocyanine in concentrated solutions has been assigned to the radical transient species generated during the photoinduced dissociation with the electron transfer between the molecules of phthalocyanines. The emission at 527 nm in DMSO and at 556 nm in water has been preliminarily assigned to the fluorescence from the higher excited triplet state Tn→T1.