Photoinduced self-organization of donor–acceptor complex intended for oxidative splitting of water

Abstract

The ground and excited states of complexes combined on the base of associated forms of meso-tetra( p-aminophenyl)porphine (TAPP) and donor–acceptor complex formed between triethylamine and manganese(II), in which manganese(II) moiety of the complex possessing Δ H pp=70 mT was preliminary transformed into the EPR-silent form, are investigated by absorption and luminescence spectroscopy. According to absorption and fluorescence spectra dramatic photoinduced transformation of the combined complex in the presence of NaHCO 3 is found under illumination with a non-stop change of exciting light wavelength from red to ultraviolet. Absorption spectrum (before the transformation) had a broad Soret band with the maximum at 433 nm, where the associated state of the porphyrin is preliminary estimated as a trimer. The complex obtained after the transformation has the components of monomeric porphyrin with the maximum of Soret band at 418 nm in the spectrum and porphyrin dimer coordinated with the manganese ions. The dimer has a broad Soret band with λ max=467 nm and a broad red band with the maximum at ca. 780 nm in the absorption spectrum, although none of these bands are observed in the spectrum before the illumination. Selective excitation into these Soret bands and the intermediate region, reveals well-known fluorescence of monomeric porphyrin, which is similar to that of tetraphenylporphine, and a strong IR emission with the maximum at 875–880 nm. The relationship between the fluorescence of the monomeric porphyrin and the IR emission depends on the wavelength of excitation. The results of the study of the combined complexes allow to conclude that the photoprocess of water oxidation takes place in the combined complex formed between associates of TAPP and EPR-silent manganese–triethylamine complex.