Excited State Properties of Rh2(O2CCH3)4: Solution Photochemistry and Photoinitiated DNA Cleavage

Abstract The photophysical properties of Rh2(O2CCH3)4(L)2 (L = CH3OH, THF = tetra-hydrofuran, PPh3 = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. All the complexes exhibit a long-lived transient absorption signal (τ = 3.5–5.0 μs) assigned as an electronic excited state of each molecule. An optical transition at −760 nm is observed in the spectra of the transients, whose position is relatively independent of axial ligand. No emission from the Rh2(O2CCH3)4(L)2 (L = CH3OH, THF, PPh3, py) systems was observed at room temperature or at 77 K, but energy transfer from excited Rh2(O2CCH3)4(PPh3)2 to tetracene and perylene takes place to form the 3ππ∗ excited state of each acceptor. Electron transfer from ∗Rh2(O2CCH3)4(PPh3)2 to dimethyl viologen (MV2+) and chloro-p-benzoquinone (Cl-BQ) takes place with quenching rate constants (kq) of 8.0 × 106 M−1s−1 and 1.2 × 106 M−1s−1 in methanol, respectively. A kq value of 2 × 108 M−1s−1 was measured for the quenching of the excited s...