Achieving NIR circularly polarized luminescence (CPL) by triad change of d10 systems

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Chiral photoactive compounds that exhibit circularly polarized luminescence (CPL) in the near-IR (λem > 700 nm) from triplet excited states have the potential to greatly influence the development of possibly game-changing technologies, such as quantum computing and cryptography, spintronics, and biosensors. The challenges to design molecular systems suitable for such applications based on electroluminescence are manifold, with a particularly intriguing intellectual dilemma related to the mutually exclusive prerequisites for simultaneously high luminescence efficiency and high dissymmetry of left and right polarized emission. Molecular low-energy emitters typically suffer significantly from non-radiative decay according to the energy gap law, and thus high radiative rate constants k(r) (i.e. high electric transition dipole moments) are mandatory to outcompete k(nr). However, CPL with a high dissymmetry factor g(lum) requires a large magnetic transition dipole moment, that is detrimental to k(r). Thus, a very fine balance needs to be found between these two properties to efficiently harvest triplet states in the NIR for chiroptical applications. While d10 metal complexes of group 11 typically exhibit LLCT/MLCT excited states, group 12 compounds are dominated by LLCT/LMCT electronic structures and it has been found that there are severe limitations to achieve NIR emission with high k(r). In contrast, group 10 complexes bearing strongly donating ligands benefit from high oxidation potentials, allowing for very low energy MLCT states with high spin-orbit coupling. Thus, within this collaborative project, we aim to combine our expertise in the fields of synthetic chemistry, spectroscopy and theoretical chemistry to construct chiral highly efficient (Ni0/Pd0/Pt0) luminophores in linear and trigonal coordination geometries, of which the dissymmetry of the triplet state emission is fine-tuned by the ligand environment. Suitable candidate compounds will be tested in proof-of-concept applications such as NIR-CPL-OLEDs or non-classical single-photon sources.