Synthesis, characterization, photophysical and electrochemical properties of rhenium(I) tricarbonyl diimine complexes with triphenylphosphine ligand

Abstract

In this work, the compounds fac-[ReL(CO)3(NN)]0/+1, NN=1,10-phenanthroline, phen, 4,7-dimethyl-1,10-phenanthroline, Me2phen, or 4,7-dimethoxy-1,10-phenanthroline, (MeO)2phen, and L=Cl− or triphenylphosphine, PPh3, were synthetized and characterized by 1H NMR, UV–vis and FTIR spectroscopies and their photophysical properties were investigated by steady-state and time-resolved emission spectroscopies. All complexes displayed strong absorption in the high energy UV-region assigned to intraligand transitions, ILNN, and the lower energy band was ascribed to a metal-to-ligand charge transfer, MLCTRe→NN. The two electron donor groups attached to phen ligand shifted the emission maxima of the complexes to higher energy as the substituent becomes more electron donor, consequently the contribution of the 3ILNN on the 3MLCT emission becomes more evident. This effect is enhanced by coordinating the electron-withdrawing PPh3 ligand on Re(I) complexes (λmax=515nm, ϕ=13%, τ=2.52μs for phen; λmax=512nm, ϕ=8.2%, τ=2.00μs for Me2phen; λmax=478 and 506nm, ϕ=1.1%, τ=1.12μs for (MeO)2phen). This interference is supported by the small shift of the emission maxima and two lifetimes in the μs domain observed for substituted-phen complexes in PMMA films. The photophysics of Re(I) compounds reported herein provides new insights into the understanding of electron-donor groups on the phen ligand that are relevant to practical and fundamental development of photoinduced molecular devices.