Broad-Band NIR Transient Absorption Spectroscopy of an “All-Carbon”-Bridged Bimetallic Radical Cation Complex

Broad-band near-infrared (NIR) transient absorption (TA) spectroscopy has been used for the first time to probe an all-carbon-bridged organometallic radical cation complex. The compound [{Ru­(PPh3)2Cp}2(μ-CCCC)]+ ([1]+) was investigated in dichloromethane and acetonitrile solutions, using laser excitation at 700, 800, 900, and 1000 nm; these wavelengths span the NIR absorption band envelope. The resulting TA spectra were found to be independent of excitation wavelength and consist of an excited state absorption feature with a peak at ca. 1150 nm and the corresponding bleach signal of the ground-state NIR absorption band, which both decay to 0 over the 50 ps time window investigated. Data were analyzed globally and fit collectively for each of the four different excitation wavelengths, with the resulting best fit to a biexponential decay function indicating two processes with slightly different time scales of ca. 1.5 and ca. 9.0 ps involved in the relaxation to the ground state.