Synthesis, Characterization, and Photochemical and Computational Investigations of Ru(II) Heterocyclic Complexes Containing 2,6-dimethylphenylisocyanide (CNx) Ligand

The isocyanide ligand forms complexes with ruthenium(II) bis-bipyridine of the type [Ru(bpy)2(CNx)Cl](CF3SO3) (1),
[Ru(bpy)2(CNx)(py)](PF6)2 (2), and [Ru(bpy)2(CNx)2](PF6)2 (3) (bpy = 2,2‘-bipyridine, py = pyridine, and CNx =
2,6-dimethylphenylisocyanide). The redox potentials shift positively as the number of CNx ligands increases. The
metal-to-ligand charge-transfer (MLCT) bands of the complexes are located at higher energy than 450 nm and
blue shift in proportion to the number of CNx ligands. The complexes are not emissive at room temperature but
exhibit intense structured emission bands at 77 K with emission lifetimes as high as 25 μs. Geometry optimization
of the complexes in the singlet ground and lowest-lying triplet states performed using density functional theory
(DFT) provides information about the orbital heritage and correlates with X-ray and electrochemical results. The
lowest-lying triplet-state energies correlate well with the 77 K emission energies for the three complexes. Singlet
excited states calculated in ethanol using time-dependent density functional theory (TDDFT) and the conductor-like
polarizable continuum model (CPCM) provide information that correlates favorably with the experimental absorption
spectra in ethanol.