Theoretical studies of structures and spectroscopic properties of [(tpy)(bpy)RuC CC6H4R]+ (tpy=2,2′:6′,2"-terpyridine, bpy=2,2′-bipyridine; R = F, Cl, H, Me and OMe)

A series of polypyridine ruthenium (II) acetylide complexes, [(tpy)(bpy)RuC CC6H4R](+) (tpy = 2,2 ':6 ',2 ''-terpyridine, bpy = 2,2 '-bipyridine; R = F (1), Cl (2), H (3), Me (4) and OMe (5)) are investigated theoretically to explore their electronic structures and spectroscopic properties. Their ground/excited state geometries, electronic structures and spectroscopic properties are first calculated using density functional theory (DFT) and time-dependent DFT (TDDFT). The absorption and emission spectra of the complexes in acetonitrile solution are also obtained by using TDDFT (B3LYP) method associated with the CPCM model. The calculations show that the energy levels of HOMOs for 1-5 are sensitive to the substituent on phenylacetylide ligand and increase with the same order of the electron-donating ability of the substituents; however, those of polypyridine-based LUMOs vary slightly. The lowest-energy absorptions and emissions for 1-5 are progressively red-shifted in the order of 1 approximate to 2 < 3 < 4 < 5 when the electron-donating groups are introduced into the phenylacetylide ligand. The phosphorescence of 1 are attributed to {[d (xz) (Ru) + pi(Ca C)]->[pi*(tpy)]} ((MLCT)-M-3/(LLCT)-L-3) transition, whereas those of 2-5 are originated from {[d (xz) /d (xy) (Ru)+pi(Ca C)+pi(C6H4R)]->[pi*(tpy/bpy)]} ((MLCT)-M-3/(LLCT)-L-3) transitions.