Metalated Ir(III) Complexes Based on the Luminescent Diimine Ligands: Synthesis and Photophysical Study

• Published in: Inorganic chemistry Vol. 57; no. 12; pp. 6853 - 6864
• Main Authors: Shakirova, Julia R, Tomashenko, Olesya A, Galenko, Ekaterina E, Khlebnikov, Alexander F, Hirva, Pipsa, Starova, Galina L, Su, Shih-Hao, Chou, Pi-Tai, Tunik, Sergey P
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18-06-2018
• DOI: 10.1021/acs.inorgchem.8b00390
• EISSN: 1520-510X
• ISSN: 0020-1669

A series of novel diimine (N∧N) ligands containing developed aromatic [2,1-a]­pyrrolo­[3,2-c]­isoquinoline system have been prepared and used in the synthesis of Ir­(III) luminescent complexes. In organic solvents, the ligands display fluorescence which depends strongly on the nature of solvents to give moderate to strong orange emission in aprotic solvents and shows a considerable blue shift and substantial increase in emission intensity in methanol. Insertion of electron-withdrawing and -donating substituents into peripheral phenyl fragment has nearly no effect onto emission parameters. The ligands were successfully used to prepare the metalated [Ir­(N∧C)2(N∧N)]+ complexes (where N∧C = phenylpyridine (N∧C-1), p-tolylpyridine (N∧C-2), 2-(benzo­[b]­thiophen-2-yl)­pyridine (N∧C-3), 2-benzo­[b]­thiophen-3-yl)­pyridine (N∧C-4), and methyl 2-phenylquinoline-4-carboxylate (N∧C-5)) using standard synthetic procedures. The complexes obtained display moderate to strong phosphorescence in organic solvents; the emission characteristics is determined by the nature of emissive triplet state, which varies substantially with the variations in the structure and donor properties of the C- and N-coordinating functions in metalating ligands. TD-DFT calculations show that for complexes 1, 2, and 4 the emission originates from the mixed 3MLCT/3LLCT excited states with the major contribution from the aromatic moiety of the diimine ligand, whereas in 3 the emissive triplet manifold is mainly located at the N∧C ligand to give structured emission band typical for the ligand centered (LC) excited state. In the case of 5, the phosphorescence may be also assigned to the mixed 3MLCT/3LLCT excited state; however, the major contribution is attributed to the aromatic moiety of the metalating N∧C ligand.