New luminescent cyclometalated iridium complexes prepared by the post-synthetic modification

Abstract

Luminescent heteroleptic bis-cyclometalated iridium(III) complexes, [Ir(ppy)2(RPh-phen)](PF6) (Hppy=2-phenylpyridine; RPh-phen=5-(4′-R-substituted phenyl)-1,10-phenanthroline, R=H for 3, tBu for 4, and CF3 for 5), have been synthesized via Suzuki–Miyaura cross coupling reaction of the corresponding boronic acids with [Ir(ppy)2(X-phen)]Cl (X-phen=5-halogen-1,10-phenanthroline, X=Cl for 1 and Br for 2) and structurally characterized via single crystal X-ray diffraction analysis. Spectroscopic analyses and density functional calculations revealed that 3-5 in CH2Cl2 show intense orange emission with long emission lifetimes (τ=708–784ns) and high quantum yields (Φ=23.6–40.6%) that originate from a T1→S0 transition from the phen moiety to the Ir(ppy)2 moiety. Cyclic voltammetry analyses elucidated that 3-5 have reversible 1e− reduction and oxidation waves. The photosensitizing properties of 1-5 as well as [Ir(ppy)2(phen)](PF6) (6; phen=1,10-phenanthroline) were also analyzed via Stern-Volmer plots and photoreduction reactions of protons to yield hydrogen (H2). These results revealed that 3 is a promising photosensitizer for photochemical H2 evolution reaction that is comparable to 6.