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School of Chemistry Colloquium: Prof. Andreas Steffen (Technische Universität Dortmund) Towards Cu(I)- and Zn(II)-based low-energy CPL triplet emitters and their application as non-classical single photon sources

The investigation of photoactive transition metal complexes based on abundant 3d elements to substitute established IrIII- or PtII-compounds as triplet excited state emitters for photonic applications is a rapidly growing field.[1] Copper(I) complexes are very promising candidates as their d10 configuration hinders non-radiative decay via d-d* transitions and provides access to various coordination geometries, allowing facile tuning of the excited state properties[2] including stimulus-responsive luminescence behavior.[3] Despite the smaller spin-orbit coupling of the 3d metal ion in comparison to 5d elements, it has been shown recently that linearly coordinated CuI carbene complexes in particular are able to compete with regard to the radiative rate constants of blue to orange triplet state emission, where values for kr(T1) or kr(TADF) between 105-106 s-1 were observed.[4] However, in the fields of quantum communication and cryptography, low-energy triplet emitters in the deep red to near-IR — ideally combined with circularly polarized emission — are needed.[4a,b,5] Only very few 3d metal complexes match that energy and CPL with high kr, and quantum yields are usually well below 10%. In this contribution our design strategies and first forays towards low-energy triplet state emitters based on (chiroptical) CuI and ZnII complexes as non-classical light sources for applications involving single-molecule photon correlation will be discussed.
[1] a) Steffen, A.; Hupp, B. In Comprehensive Coordination Chemistry III; Constable, E. C., Parkin, G., Que Jr, L., Eds., Vol. 2, Elsevier, 2021, pp 466–502; b) Wenger, O. S. J. Am. Chem. Soc. 2018, 140, 13522; c) Bizzarri, C.; Spuling, E.; Knoll, D. M.; Volz, D.; Bräse, S. Coord. Chem. Rev. 2018, 373, 49; d) Hockin, B. M.; Li, C.; Robertson, N.; Zysman-Colman, E. Catal. Sci. Technol. 2019, 9, 889.

[2] a) Yersin, H.; Czerwieniec, R.; Shafikov, M. Z.; Suleymanova, A. F. ChemPhysChem 2017, 18, 3508; b) Nitsch, J.; Lacemon, F.; Lorbach, A.; Eichhorn, A.; Cisnetti, F.; Steffen, A. Chem. Commun. 2016, 2932; c) Braunschweig, H.; Dellermann, T.; Dewhurst, R. D.; Hupp, B.; Kramer, T.; Mattock, J. D.; Mies, J.; Phukan, A. K.; Steffen, A.; Vargas, A. J. Am. Chem. Soc. 2017, 139, 4887; d) Bissinger, P.; Steffen, A.; Vargas, A.; Dewhurst, R. D.; Damme, A.; Braunschweig, H. Angew. Chem. Int. Ed. 2015, 54, 4362.

[3] a) Hupp, B.; Nitsch, J.; Schmitt, T.; Bertermann, R.; Edkins, K.; Hirsch, F.; Fischer, I.; Auth, M.; Sperlich, A.; Steffen, A. Angew. Chem. Int. Ed., 2018, 57, 13671; b) Liske, A