title: Excited-state dynamics of metal string complex Ni3(dpa)4X2 from femtosecond transient absorption spectra.
abstract: The excited-state dynamics of Ni(3)(dpa)(4)X(2), in which dpa is the ligand di(2-pyridyl)amido and X = NCS or Cl, are investigated by transient absorption spectroscopy. The pi pi* and dd states are excited upon irradiation at wavelengths of 330 and 600 nm, respectively. Similar transient spectra are observed under the experimental temporal resolution. The transient species also show weak absorption. It is proposed that a low-lying metal-centered dd state is accessed immediately after excitation. Analyses of the experimental kinetic traces reveal a rapid conversion from a ligand-centered pi pi* state to a metal-centered dd state in 0.1-0.4 ps. Vibrational cooling occurs with a time coefficient of 3.0-15.9 ps. From the spectral shift observed in the transient spectra relative to the steady-state spectra, the dd state is assigned as B(1)/B(2)(Ni(t)). This dd state eventually converts to the electronic ground state, in about 100 ps for the isothiocyanate complex and 200 ps for the chloride. In this trimetal string complex, relaxation to the ground electronic surface after excitation is therefore rapid.
authors.affiliation: Department of Chemistry, National Tsing Hua University, 101 Kuang Fu Road Section 2, Hsinchu 30013 Taiwan, Republic of China.
authors.forename: Chao-Han
authors.initials: CH
authors.lastname: Cheng
authors.forename: Ruei-Ding
authors.initials: RD
authors.lastname: Hung
authors.forename: Wen-Zhen
authors.initials: WZ
authors.lastname: Wang
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng
authors.forename: I-Chia
authors.initials: IC
authors.lastname: Chen