Two new blue-phosphorescent Ir(III) cyclometalated complexes demonstrating the pushing-up effects of amino on levels of Pi-type molecular orbitals

• The orbital-based rationalization of high-energy emission of [Ir(ppy)2(N,N-ligands)] has been proposed.
• Fluoro, methoxyl and amino groups can elevate frontier MOs by different extents.
• The content of carbon subjected to fluorination explains the position-dependent effects.

Orbital interactions between nitrogen’s 2p-orbital, 2p(N), and the higher-lying HOMO/LUMO would push-up the latter even higher. This destabilization effect exerted by an amino explains the high-lying LUMO of the 2,2′-dipyridyl amine (HDPA) ancillary ligand, as well as the high-lying LUMO in Ir(ppy)2HDPA+ (ppy = 2-phenylpyridine). The pi-destabilization effect on MOs exerted by a fluoro must be incorporated into consideration to explain the site-dependent characteristics observed by related color-tuning studies. Two new blue phosphorescent fluorinated Ir(ppy)2HDPA+ complexes have been synthesized by introducing fluoro(s) at suitable phenyl-carbon(s): having small 2pπ(C) content in HOMO and/or large 2pπ(C) content in LUMO.

The LUMO in Ir(ppy)2bpy is pushed up by amino to LUMO + 7 in Ir(ppy)2HDPA. The LUMO in Ir(ppy)2HDPA comes from the stabilized LUMO + 7 in the bpy-analog. Values of crystal orbital overlap populations calculated between two pyridinyl fragments decrease in magnitudes from −0.091 au (LUMO + 7) to −0.014 au (LUMO).Figure optionsDownload as PowerPoint slide