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Phosphorescent Cationic Heterodinuclear Ir III /M I Complexes (M=Cu I , Au I ) with a Hybrid Janus‐Type N‐Heterocyclic Carbene Bridge
Author(s) -
Bonfiglio Anna,
Pallova Lenka,
César Vincent,
Gourlaouen Christophe,
BelleminLaponnaz Stéphane,
Daniel Chantal,
Polo Federico,
Mauro Matteo
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202002767
Subject(s) - phosphorescence , carbene , chemistry , cationic polymerization , excited state , denticity , ligand (biochemistry) , photochemistry , crystallography , moiety , stereochemistry , polymer chemistry , crystal structure , physics , fluorescence , atomic physics , biochemistry , receptor , quantum mechanics , catalysis
A novel class of phosphorescent cationic heterobimetallic Ir III /M I complexes, where M I =Cu I ( 4 ) and Au I ( 5 ), is reported. The two metal centers are connected by the hybrid bridging 1,3‐dimesityl‐5‐acetylimidazol‐2‐ylidene‐4‐olate (IMesAcac) ligand that combines both a chelating acetylacetonato‐like and a monodentate N‐heterocyclic carbene site coordinated onto an Ir III and a M I center, respectively. Complexes 4 and 5 have been prepared straightforwardly by a stepwise site‐selective metalation with the zwitterionic [(IPr)M I (IMesAcac)] metalloproligand (IPr=1,3‐(2,6‐diisopropylphenyl)‐2 H ‐imidazol‐2‐ylidene) and they have been fully characterized by spectroscopic, electrochemical, and computational investigation. Complexes 4 and 5 display intense red emission arising from a low‐energy excited state that is located onto the “Ir(C^N)” moiety featuring an admixed triplet ligand‐centered/metal‐to‐ligand charge transfer ( 3 IL/ 1 MLCT) character. Comparison with the benchmark mononuclear complexes reveals negligible electronic coupling between the two distal metal centers at the electronic ground state. The bimetallic systems display enhanced photophysical properties in comparison with the parental congeners. Noteworthy, similar non‐radiative rate constants have been determined along with a two‐fold increase of radiative rate, yielding brightly red‐emitting cyclometalating Ir III complexes. This finding is ascribed to the increased MLCT character of the emitting state in complexes 4 and 5 due to the smaller energy gap between the 3 IL and 1 MLCT manifolds, which mix via spin–orbit coupling.