Effect of\nthe Appended Morpholinyl Group on Photophysical\nBehavior of Mono- and Bis-cyclometalated Terpyridine Iridium(III)\nChromophores

This paper provides extensive studies of [IrCl(Ph-py)(morph-C<sub>6</sub>H<sub>4</sub>-terpy-κ<sup>3</sup>N)]PF<sub>6</sub> (<b>1A</b>), [Ir(Ph-py)<sub>2</sub>(morph-C<sub>6</sub>H<sub>4</sub>-terpy-κ<sup>2</sup>N)]PF<sub>6</sub> (<b>2A</b>), [IrCl(Ph-py)(Ph-terpy-κ<sup>3</sup>N)]PF<sub>6</sub> (<b>1B</b>), and [Ir(Ph-py)<sub>2</sub>(Ph-terpy-κ<sup>2</sup>N)]PF<sub>6</sub> (<b>2B</b>)\ndesigned to demonstrate the possibility of controlling the photophysical\nproperties of mono- and bis-cyclometalated complexes [IrCl(Ph-py)(R-C<sub>6</sub>H<sub>4</sub>-terpy-κ<sup>3</sup>N)]PF<sub>6</sub> and\n[Ir(Ph-py)<sub>2</sub>(R-C<sub>6</sub>H<sub>4</sub>-terpy-κ<sup>2</sup>N)]PF<sub>6</sub> through a remote electron-donating substituent\nintroduced into the 4′-position of 2,2′:6′,2″-terpyridine\n(terpy) via the phenyl linker. The attachment of the morpholinyl (morph)\ngroup was evidenced to induce dramatic changes in the emission characteristics\nof the monocyclometalated Ir(III) systems with <i>meridionally</i> coordinated R-C<sub>6</sub>H<sub>4</sub>-terpy ligand (κ<sup>3</sup>N). In solution, the obtained complex [IrCl(Ph-py)(morph-C<sub>6</sub>H<sub>4</sub>-terpy-κ<sup>3</sup>N)]PF<sub>6</sub> was\nfound to be a rare example of dual-emissive Ir(III) systems. Within\nthe series [Ir(Ph-py)<sub>2</sub>(R-C<sub>6</sub>H<sub>4</sub>-terpy-κ<sup>2</sup>N)]PF<sub>6</sub> bearing the R-C<sub>6</sub>H<sub>4</sub>-terpy ligand bound to the central ion in a bidentate coordination\nmode, the appended electron-donating morpholinyl group induced a minor\neffect on the emission maximum, but it was found to be an effective\ntool for extending the excited-state lifetime, further prolonging\nwith the increase of solvent polarity. The results of this work are\nof high significance for better understanding the push–pull\neffect and dual-emission phenomena in Ir-based luminophores, as well\nas developing chromophores with prolonged emission lifetimes.