Ultrafast primary processes of an iron-(iii) azido complex in solution induced with 266 nm light

Abstract

The ultrafast photo-induced primary processes of the iron-(III) azido complex, [Fe^IIIN₃(cyclam-acetato)] PF₆ (1), in acetonitrile solution at room temperature were studied using femtosecond spectroscopy with ultraviolet (UV) excitation and mid-infrared (MIR) detection. Following the absorption of a 266 nm photon, the complex undergoes an internal conversion back to the electronic doublet ground state at a time scale below 2 ps. Subsequently, the electronic ground state vibrationally cools with a characteristic time constant of 13 ps. A homolytic bond cleavage was also observed by the appearance of ground state azide radicals, which were identified by their asymmetric stretching vibration at 1659 cm⁻¹. The azide radical recombines in a geminate fashion with the iron containing fragment within 20 ps. The cage escape leading to well separated fragments after homolytic Fe–N bond breakage was found to occur with a quantum yield of 35%. Finally, non-geminate recombination at nanosecond time scales was seen to further reduce the photolytic quantum yield to below 20% at a wavelength of 266 nm.