FWF - Photocatalysis - Photocatalytic application of watersoluble metalloporphyrins

Metalloporphyrins are key compounds in nature, but their advantageous coordination, redox and photoinduced properties can also be exploited in artificial systems, e.g., in photocatalytic reactions. According to our preliminary results water-soluble sitting-atop (SAT- metalloporphyrins containing large size metal ions located out of the plane of the porphyrin ligand exhibit unique photochemistry. They undergo efficient ligand-to-metal charge-transfer reactions followed by strong absorption of visible light. This special photoactivity allows their utilization as photocatalysts in cyclic processes for chemical synthesis and in solar energy conversion reaction mechanisms. The main goal of our proposed collaboration is the elucidation of these photoredox reaction mechanisms of such water-soluble SAT metalloporphyrins. On the basis of these new results, the catalytic systems and also in-plane complexes will be checked and utilized for preparative or photochemical water-splitting procedures for renewable energy technology and green chemistry in the future. For tuning the photoactivity of SAT metalloporphyrins, we shall synthesize water-soluble SAT complexes of a series of lanthanide ions with a wide range of ionic radii, and of other larger-sized metal ions to control the out-of-plane position of the metal center. The distortion of the ligand plane will also be governed by appropriate substituents (e.g. via bromination). The photophysical and photochemical properties of the newly prepared complexes will be determined using steady-state and time-resolved absorption, emission, resonance Raman and CW- and time-resolved ESR spectroscopy as well as quantum chemical calculations. The mechanism of their photoredox reactions will be elucidated by systematically testing wide ranges of both reductive and oxidative quenchers interacting with either the excited-state metalloporphyrins or their primary photochemical intermediates (but not with each other) . The optimal metalloporphyrin/oxidant/ reductant systems will be selected for the realization of the photocatalysis in a scalable reactor designed for solar energy utilization. We plan to use the complementary equipment of the participating Austrian and Hungarian laboratories.