Phosphorescent Cationic Heterodinuclear Ir^III/M^I Complexes (M=Cu^I, Au^I) with a Hybrid Janus‐Type N‐Heterocyclic Carbene Bridge

Abstract

A novel class of phosphorescent cationic heterobimetallic IrIII/MI complexes, where MI=CuI (4) and AuI (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 IrIII and a MI center, respectively. Complexes 4 and 5 have been prepared straightforwardly by a stepwise site‐selective metalation with the zwitterionic [(IPr)MI(IMesAcac)] metalloproligand (IPr=1,3‐(2,6‐diisopropylphenyl)‐2H‐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 (3IL/1MLCT) 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 IrIII 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 3IL and 1MLCT manifolds, which mix via spin–orbit coupling.

Chiroptical activity of benzannulated N-heterocyclic carbene rhenium(i) tricarbonyl halide complexes: towards efficient circularly polarized luminescence emitters

“…14 Recently, Mauro and co-workers reported on a novel family of luminescent rhenium(I) complexes bearing a pyridyl pyridoannelated NHC ligand with 3 LC emission, belonging to the family of general formula (V) in Scheme 1. 17 Stemming from our long-standing interest in the photophysics and photochemistry of rhenium(I) tricarbonyl complexes as well as NHC-based emitters for optoelectronics, [18][19][20][21][22][23][24] we questioned whether the use of a less extended, yet benzannulated, NHC scaffold with a limited steric demand would be suitable for the construction of efficient CPL-active phosphorescent rhenium(I)-based emitters. Therefore, the purpose of the present study is to explore the effect exerted by different substituents onto the photophysical and chiroptical properties of a family of enantiopure [ReX(CO) 3 (N^C NHC )] complexes, where N^C is a benzannulated NHC deriving from a series of six (substituted) 2-(pyridin-2-yl)imidazo [1,5-a]pyridin-2-ium pro-ligands (Schemes 1 and 2).…”