Effect of the Appended Morpholinyl Group on Photophysical Behavior of Mono- and Bis-cyclometalated Terpyridine Iridium(III) Chromophores

This paper provides extensive studies of [IrCl(Ph-py)(morph-C₆H₄-terpy-κ³N)]PF₆ (1A), [Ir(Ph-py)₂(morph-C₆H₄-terpy-κ²N)]PF₆ (2A), [IrCl(Ph-py)(Ph-terpy-κ³N)]PF₆ (1B), and [Ir(Ph-py)₂(Ph-terpy-κ²N)]PF₆ (2B) designed to demonstrate the possibility of controlling the photophysical properties of mono- and bis-cyclometalated complexes [IrCl(Ph-py)(R-C₆H₄-terpy-κ³N)]PF₆ and [Ir(Ph-py)₂(R-C₆H₄-terpy-κ²N)]PF₆ through a remote electron-donating substituent introduced into the 4′-position of 2,2′:6′,2″-terpyridine (terpy) via the phenyl linker. The attachment of the morpholinyl (morph) group was evidenced to induce dramatic changes in the emission characteristics of the monocyclometalated Ir(III) systems with meridionally coordinated R-C₆H₄-terpy ligand (κ³N). In solution, the obtained complex [IrCl(Ph-py)(morph-C₆H₄-terpy-κ³N)]PF₆ was found to be a rare example of dual-emissive Ir(III) systems. Within the series [Ir(Ph-py)₂(R-C₆H₄-terpy-κ²N)]PF₆ bearing the R-C₆H₄-terpy ligand bound to the central ion in a bidentate coordination mode, the appended electron-donating morpholinyl group induced a minor effect on the emission maximum, but it was found to be an effective tool for extending the excited-state lifetime, further prolonging with the increase of solvent polarity. The results of this work are of high significance for better understanding the push-pull effect and dual-emission phenomena in Ir-based luminophores, as well as developing chromophores with prolonged emission lifetimes.