Peculiar photoinduced properties of water-soluble, early lanthanide (III) porphyrins

Water-soluble, early lanthanide(III) mono- and bisporphyrin complexes possess very similar UV-Vis absorption as well as photophysical and photochemical properties, as a consequence of a special type of aggregation, through the peripheral substituents. In the absence of the bidentate, O-donor acetate ligand, bisporphyrin can form too, which has slightly redshifted and broadened absorption bands, compared to those of the monoporphyrin. Also the bisporphyrin displays a blueshifted and less intense fluorescence, related to the free-base porphyrin. The formation of complexes and the transformation between the mono- and bisporphyrins are very slow reactions in dark at room temperature. These reactions are accelerated by the photolysis of the system, which are considerable by-processes of the photoredox degradation. Depending on the wavelength of irradiation, two types of photoproducts can appear: during the photolysis at the Soret-band, a radical type intermediate can be observed, which disappears in dark. However, during the irradiation at the Q-bands, a new photoproduct appears, which is stable in dark and undetectable in the case of post-transition metal ions' out-of-plane porphyrin complexes. (C) 2014 Elsevier B.V. All rights reserved.