Electronic structures and spectral properties of rhenium(I) tricarbonyl diimine complexes with phosphine ligands: DFT/TDDFT theoretical investigations

The ground and excited state geometries and frontier molecular orbital, absorption and emission properties of the four transition metal complexes Re(bpy)(CO)3(PEt3)+ (1), Re(bpy)(CO)3(PPh3)+ (2), Re(bpy)(CO)3[P(OEt3)]+ (3) and Re(bpy)(CO)3[P(OPh3)]+ (4) were studied theoretically. The introduction of different phosphine ligands significantly changed the geometric parameters of the complexes. The axial Re–C bond distance was longer than the equatorial Re–C bond distance. The lowest lying absorption bands of 1 and 2 have HOMO → LUMO transition configurations resulting in MLCT/LLCT transition characteristics. The HOMO-1 → LUMO transition predominantly contributed to the lowest absorption bands of 3 with MLCT/LLCT characteristics. The absorption band of 4 at 326 nm was dominated by HOMO-4 → LUMO and HOMO-6 → LUMO transitions with mixed MLCT/LLCT characteristics. The phosphorescence emission energies of 1–4 were also calculated and compared with the experimental values.