Acid-base-induced fac→mer isomerization of luminescent Ir(III) complexes Anastasia Gitlina and Kay Severin École polytechnique fédérale de Lausanne (EPFL), Switzerland Iridium(III) complexes are of everlasting interest due to their unique chemical, photochemical and photophysical properties including remarkable chemical and thermal stability, reversible redox transformations, high luminescence quantum yields, and easily tunable emission colour and lifetime. These features have allowed these complexes to be widely used in optoelectronics, photonics, photoredox catalysis, oxygen and sensing etc. [1] Structurally, luminescent Ir(C^N) 3 complexes (C^N = cyclometalated arylpyridyl ligand) exist as two stable geometrical isomers with distinct photophysical properties: facial ( fac ) and meridional ( mer ). [2] The mer isomer tends to be thermodynamically less stable than the fac isomer. Varying the reaction conditions, the mer isomer can be obtained in a kinetically controlled reaction and transformed to the fac form at high temperatures or under light irradiation. [3] The back fac → mer isomerization has not been reported so far. Herein we show that fac -Ir(C^N) 3 complexes can be converted into their mer isomers by a successive reaction with acid and then base. [4] The chemically induced fac → mer isomerization is fast, clean, quantitative, tolerant to different substituents, stereoselective, and it can be reversed by light irradiation. The cleanliness and reversibility of the new fac → mer isomerization provide the possibility to use luminescent Ir(C^N) 3 complexes as substrates for rewritable data storage devices or as a basis for molecular machines. Another application direction of this isomerization is the synthetic accessibility of mer isomers, which are difficult to prepare using published procedures. The authors greatly appreciate a financial support from Swiss National Science Foundation (SNSF) and EPFL as well as facility/equipment available within EPFL. References 1. E. Zysman-Colman, Iridium(III) in Optoelectronic and Photonics Application, John Wiley & Sons , Chichester, West Sussex, 2017 .
2. A. Tamayo, B. Alleyne, P. Djurovich, J. Am. Chem. Soc ., 2003 , 125 , 7377. 3. A. McDonald, M. Lutz, L. von Chrzanowski, Inorg. Chem ., 2008 , 47 , 6681. 4. A. Gitlina, F. Fadaei-Tirani, A. Ruggi, Chem. Sci ., 2022 .
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