Photoinduced Redox Processes in Phthalocyanine Derivatives by Resonance Raman Spectroscopy

Photochemical and photophysical behavior of copper(II) phthalocyanine-3,4',4'',4'''-tetrasulfonate anion Cu(tsPc) 4 - irradiated with the visible light from the range 465-514 nm (vis) has been studied by resonance Raman spectroscopy. The photochemistry of monomers and dimers of Cu(tsPc) 4 - has been studied in liquid solutions of H 2 O and dimethyl sulfoxide (DMSO) as well as in crystal and glassy frozen matrixes as a function of temperature in the range 293-77 K. We have identified the transient species of the photoredox dissociation as ligand radicals Cu I I (tsPc . ) 3 - and Cu I I (tsPc . ) 5 - . We have shown that the photoinduced dissociation with the electron transfer between the molecules of phthalocyanine is determined mainly by the molecular structure. The electron transfer that leads to the generation of the ligand-centered radicals may occur only for the ring-stacked structures with strong overlapping between the π-electronic clouds of the macrocycle rings of the adjacent molecules. These structures exist in highly concentrated aqueous solutions and in the crystal phases. The photoinduced electron transfer does not occur for the monomers of Cu(tsPc) 4 - in DMSO solution and in the glassy phases. We have assigned the emission at 527 nm for Cu(tsPc) 4 - in DMSO and at 556 nm in H 2 O to the T n → T 1 fluorescence. Competitively, the higher excited triplet state T n state (or the first excited singlet state S 1 ) participates in photoinduced redox dissociation Cu(tsPc) 4 - → h v Cu I I (tsPc . ) 3 - + Cu I I (tsPc . ) 5 - . The vis irradiation of the Cu I I (tsPc . ) 3 - and Cu I I (tsPc . ) 5 - radicals excites them to the lowest lying excited states that emit fluorescence at 682 nm after undergoing to the ground states.