Phosphorescent Cyclometalated Platinum(ii) Hexahydroimidazo[1,5‐a]pyridinylidene Complexes

Abstract

The synthesis of N-heterocyclic carbene precursors based on the hexahydroimidazo[1,5-a]pyridine and their corresponding cyclometalated platinum(II) carbene complexes is reported. All compounds are fully characterized by standard techniques and additionally X-ray structures could be obtained for three complexes. The photophysical properties of these platinum complexes were investigated by absorption and photolumines-cence measurements. All complexes showed strong phosphorescence at room temperature in the sky-blue area with quantum yields of up to 71 %. Additionally, their electrochemical properties were examined by voltammetry experiments. All results were rationalized by quantum chemical DFT calculations (PBE0/6-311G*).

Phosphorescent Platinum(II) Complexes with a Spiro‐fused Xanthene Unit: Synthesis and Photophysical Properties

“…Computational results suggest that this signal is attributed to the LUMO on the β-diketonate. [84,87,88] Then, at higher voltage, multiple irreversible events take place. A characteristic signal for this class of platinum(II) complexes with fluorene or xanthene scaffolds as part of the C^C*-ligand (Scheme 1) is found at À 2.9 V. [84] A similar voltammogram with multiple events at higher voltage (from À 2.9 V) was recorded for complex 6.…”

“…This effect is often observed for the mesacac ligand, but still lacks a reliable explanation. [17,[85][86][87][88] Recently, we found that the cyclometalating fluorene motif of the SBF building block is able to neutralize the influence on the photophysical properties of the mesacac auxiliary ligand. [84] By synthesizing the corresponding regioisomers of the 2'-SFX complexes, we obtained an ideal platform for the rigorous study of this effect.…”

Luminescent Platinum(II) Complexes with a Tridentate Caffeine‐Based NHC‐Pincer Ligand: Synthesis, Electrochemistry and Photophysics

“…[6] In particular, cyclometalating variants of these ligands, in which at least one of the pyridine rings is replaced by a phenyl one, have attracted chemistry, [34][35][36] but also with respect to opto-electronic applications Pt(II) complexes with NHC ligands have been studied. [37] In this respect, the NHC moiety might either represent a monodentate ligand [35,38] or be a part of a bidentate, [39][40][41][42][43] tridentate [44][45] or even tetradentate ligand framework. [46][47] In the overwhelming majority of the published studies imidazole or one of its derivatives (e. g., benzo[d]imidazole) is employed as the NHC precursor.…”

C^C* Platinum(II) Complexes with Bis(pyridyl)borate Ligands: Synthesis, Crystal Structures, and Properties

“…We as well as other research groups have established a class of such ligands in emissive transition metal complexes in the past decade, namely cyclometalated N -heterocyclic carbene (C^C*) ligands. ,− As derivatives of the more common 2-phenylpyridines (C^N), the C^C* ligands help to facilitate more energy-rich emissions due to the stronger donor effect of the carbene motif. In addition to the extensive variation of the cyclometalated NHC ligands, − we investigated the influences of different auxiliary ligands on the emission properties of emissive platinum(II) complexes in several studies. − More recently, we successfully used bis(pyrazolyl)borate ligands as auxiliary ligands, resulting in excellent phosphorescent platinum emitters. , To further explore the applicability of borate ligands in photophysically active complexes, we chose to use bis(pyridyl)borate ligands. Transition metal complexes with bis(pyridyl)borates − and tris(pyridyl)borates − have been known for more than 20 years.…”