Micromodulating the Electronic Coupling Across Redox-Active Ferrocenyl Spacer in Binuclear Ruthenium(II) Terpyridine Complexes: Synthesis, Electrochemistry, and Photophysical Properties

The electrochemical and photophysical properties of [(X-tpy)Ru(tpy-(fc)2-tpy)Ru(X-tpy)] (tpy ) terpyridyl; X ) -H (1a), -OCH3 (1b), -Cl (1c); fc ) ferrocenyl) and [(X-tpy)Ru(tpy-CtC-(fc)2CtC-tpy)Ru(X-tpy)] (X ) -H (2a), -OCH3 (2b), -Cl (2c)) are described. The ground-state HOMO and LUMO energies were probed by electrochemical measurements. The excited-state photophysical properties were probed by UV–vis absorption spectroscopy and luminescence spectroscopy. Complexes of 1a-c are nonemissive (λexc 480–580 nm) in deoxygenated pure CH3CN or H2O/CH3CN (4/1) solution at 25 °C. Complexes 2a-c have room-temperature luminescence in H2O/CH3CN (4/1) solution. On comparison of the luminescent properties of 2b,c with those of 2a, the attachment of -OCH3 and -Cl substitutents causes a decrease of luminescence quantum yields and triplet lifetimes.