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 (<b>1A</b>), [Ir(Ph-py)₂(morph-C₆H₄-terpy-κ²N)]PF₆ (<b>2A</b>), [IrCl(Ph-py)(Ph-terpy-κ³N)]PF₆ (<b>1B</b>), and [Ir(Ph-py)₂(Ph-terpy-κ²N)]PF₆ (<b>2B</b>) 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 <i>meridionally</i> 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.