A Highly Efficient Red‐Emitting Ruthenium Complex with 3,5‐Difluorophenyl Substituents

Abstract Five 3,5‐difluorophenyl‐substituted ruthenium complexes [Ru(bpy) 2 (dfpbpy)(ClO 4 ) 2 ] (Ru‐Fbpy‐bpy; bpy=bipyridine, dfpbpy=5,5′‐di(3,5‐difluorophenyl)‐2,2′‐bipyridine), [Ru(dpp) 2 (dfpbpy)(ClO 4 ) 2 ] (Ru‐Fbpy‐dpp; dpp=4,7‐diphenyl‐1,10‐phenanthroline), [Ru(dpp) 2 (dfpphen)(ClO 4 ) 2 ] (Ru‐Fphen‐dpp; dfpphen=5,5′‐di(3,5‐difluorophenyl)‐1,10‐phenanthroline), [Ru(dpp) 2 (4,7‐dfpphen)(ClO 4 ) 2 ] (Ru‐Fdpp‐dpp; 4,7‐dfpphen=4,7‐di(3,5‐difluorophenyl)‐1,10‐phenanthroline), and [Ru(4,7‐dfpphen) 3 (AsF 6 ) 2 ] (Ru‐Fdpp) were synthesized, and their photophysical, electrochemical, and electroluminescent properties were studied systematically. The introduction of the electron‐withdrawing group 3,5‐difluorophenyl leads to a redshift of the emission of the ruthenium complexes. In addition, the 3,5‐difluorophenyl substituent extends the π conjugation of the ligand, and thus facilitates the metal‐to‐ligand charge‐transfer process of the complexes. All the complexes display orange‐red phosphorescent emissions centered at 638, 638, 624, 614, and 605 nm, respectively. Density functional theory calculations show that the lowest unoccupied molecular orbital of Ru‐Fbpy‐dpp, Ru‐Fphen‐dpp, and Ru‐Fdpp‐dpp are all distributed on the 3,5‐difluorophenyl‐substituted ligand. By using these complexes as emitters, highly luminescent single‐layer devices are obtained. The optimized device based on Ru‐Fdpp exhibits the highest luminous efficiency and power efficiency of 4.19 cd A −1 and 1.46 lm W −1 , respectively.