PhotonUp4Cat - Novel upconversion systems for photocatalysis with low energy photons

• Applicant: Professor Dr. Christoph Kerzig
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 466117789

Photochemical upconversion via the so-called sensitized triplet-triplet annihilation mechanism is capable of pooling the energy of two visible photons in order to generate a highly energetic excited state. Given that this two-photon mechanism can be driven by very low light intensities, as provided by the sun or conventional LEDs, several applications in the fields of catalysis, photobiology (medicine) and energy conversion become feasible under particularly mild conditions, which keeps fascinating numerous scientists.Starting from our exploratory investigations, we intend to bring about two novel concepts related to upconversion. The combination of meaningful spectroscopic techniques with preparative as well as mechanistic irradiation experiments should facilitate overcoming inherent difficulties, thereby paving the way for groundbreaking results in this highly competitive field. The first part of this project is concerned with the conversion of visible light to UV photons with unprecedented efficiencies and photon energies (more than 4 eV). This upconversion access to UVB light, which is practically not contained in the terrestrial solar spectrum and typically produced by environmentally hazardous lamps, will be used for the degradation of pollutants and for photocatalysis applications. Novel biphenyl-based annihilators will act as key species to break the current singlet-state energy record in upconversion and to study and exploit fundamentally new effects, e.g., regarding solvent dependences. The second part is devoted to establishing an upconversion-based reactivity control approach, which enables to switch between oxidative and reductive reactivity simply by changing the light intensity. The envisaged upconversion systems consist of a highly reducing sensitizer (activated at low intensities), whereas the excited annihilator singlet, only produced at higher light intensities, acts as a strong photooxidant. Combining this reactivity switch methodology with several different catalytic photoredox reactions is the goal of this subproject.The expected results of this project will decisively contribute to the development of more sustainable photochemical processes, in which sustainability is addressed by avoiding mercury-based UV light sources and by relying on versatile catalytic mechanisms.

• DFG Programme: Research Grants