Synthesis, Functionalization, Characterization, and Photophysical Study of Carbonyl-Containing Isocyano Rhenium(I) Diimine Complexes

New classes of tunable rhenium(I) diimine luminophores with formula of [Re(CO)(CNR)3(N–N)]PF6 and [Re(CO)(Lx)(CNC6H4Cl-4)2(1,10-phenanthroline)]PF6, (R = C6H5, 4-BrC6H4, 4-ClC6H4, 4-MeOC6H4, 2,6-iPr2C6H3; N–N = 1,10-phenanthroline, 5,6-dibromo-1,10-phenanthroline, 4,4′-di-tert-butyl-2,2′-bipyridine; Lx = MeCN, pyridine and PPh3) have been synthesized. Different synthetic routes including photo-ligand substitution and thermal carbonyl ligand substitution through the oxidative decarbonylation with trimethyl amine N-oxide, for the facial and meridional isomeric forms of [Re(CO)(CNR)3(N–N)]PF6 were investigated. On the basis of these synthetic strategies, different ligand modification and functionalization of the rhenium(I) diimine luminophores with tailored excited state properties could be readily achieved. The structures of both facial and meridional conformations of [Re(CO)(CNR)3(N–N)]PF6 and the complex precursors fac-[Re(CO)3(CNC6H3iPr-2,6)3]OTf were determined by X-ray crystallography. These complexes display an orange to red 3MLLCT [dπ(Re) → π*(N–N)] phosphorescence at room temperature. Detailed photophysical investigations revealed that the physical, photophysical, electrochemical, and excited state properties can be fine-tuned and tailored through the modifications of the substituents on isocyanide or diimine ligands.