Cu diimine complexes present a noble metal free alternative to classical Ru, Re, Ir and Pt based photosensitizers in solution photochemistry, photoelectrochemical or dye-sensitized solar cells. Optimization of these dyes requires understanding of factors governing the key photochemical properties: excited state lifetime and emission quantum yield. The involvement of exciplex formation in the deactivation of the photoexcited state is a key question. We investigate the excited-state structure of two Cu complexes using pump–probe X-ray absorption spectroscopy (XAS) and DFT. Features of XAS that distinguish flattened tetrahedral site and 5-coordinated geometry with an additional solvent near Cu(II) center are identified. Pump–probe XAS demonstrates that for both complexes the excited state is 4-coordinated. If Cu-coordinating ligand is relatively small (dimethilphenanthroline) the exciplex can be involved in deactivation pathways as a non-observable state that forms slower than it decays. Shielding of Cu center from solvent molecule using bulky ligand reduces distortions in the excited state and leads to 3 orders of magnitude longer excited-state lifetime.
Contact
Dr. Grigory Smolentsev
SuperXAS beamline
Operando spectroscopy
Swiss Light Source, Paul Scherrer Intitute
5232 Villigen-PSI, Switzerland
Telephone: +41 56 310 51 73
E-mail: grigory.smolentsev@psi.ch
Original Publication
Alexander Guda, Johannes Windisch, Benjamin Probst, Jeroen A. van Bokhoven, Roger Alberto, Maarten Nachtegaal, Lin X. Chen and Grigory Smolentsev "Excited-state structure of copper phenanthroline-based photosensitizers" Phys Chem Chem Phys 23 (2021) 26729-26736 https://doi.org/10.1039/D1CP02823E