A series of complexes of the type [Ru(tpy)(bpy)(4-R-py)]2+, where tpy = 2,2';6',2"-terpyridine, bpy = 2,2'-bipyridine, and 4-R-py = pyridine (py, 1), 4-methoxypyridine (4-MeO-py, 2), 4-acetylpyridine (4-Ac-py, 3) 4-aminopyridine (4-NH2-py, 4), and 4-trifluoromethylpyridine (4-CF3-py, 5) were synthesized and the effect of the electron donating methoxy and acetyl groups and the electron withdrawing amino and trifluoromethyl groups on the ground and excited state properties were compared. Cyclic voltammetry shows that 2 and 3 are more easily oxidized compared to 1, and that 4 and 5 have an increased oxidation potential. Electronic absorption spectra show a detectable red shift of the metal-to-ligand charge transfer (1MLCT) of 2 and 3 as compared to 1. Additionally, the 1MLCTs of 4 and 5 are blue shifted relative to 1. Complexes 1, 2, and 3 exhibit phosphorescence with quantum yields of 0.0032, 0.0046, and 0.0060 respectively. Complexes 4 and 5 are more weakly emissive with 4 having a quantum yield of &lt;0.0006 and 5 being undeterminable. Upon irradiation in CH3CN (λirr &gt; 395 nm) all five complexes undergo photoinduced ligand exchange with CH3CN to form [Ru(tpy)(bpy)(CH3CN)]2+. This process happens more rapidly in 4 (30 mins) and 5 (10 mins) compared to 1 (90 mins), 2 (240 mins) and 3 (&gt;24 hours). The data indicates that it is possible to tune the excited state properties by varying the substituents of the pyridine ring. Moving forward, this study will investigate the effect of adding electron donating and withdrawing groups to the bidentate and tridentate ligands.

Tuning excited state properties of Ru(II) complexes with a 4-substituted pyridine ligand

251st National Meeting (2016)

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