Excited-state properties of Rh2(O2CCH3)4(L)2 (L = CH3OH, THF, PPh3, py)

The photophysical properties of Rh-2(O2CCH3)(4)(L)(2) (L = CH3OH, THF = tetrahydrofuran, PPh3 = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. Time-resolved absorption shows that all the complexes possess a long-lived transient (3.5-5.0 Cls) assigned as an electronic excited state of the molecules, and they exhibit an optical transition at similar to 760 nm whose position is independent of axial ligand. No emission from the Rh-2(O2CCH3)(4)(L)(2) (L = CH3OH, THF, PPh3, py) systems was detected, but energy transfer from *Rh-2(O2CCH3)(4)(PPh3)(2) to the (3)pi pi* excited state of perylene is observed. Electron transfer from *Rh-2(O2CCH3)(4)(PPh3)(2) to 4,4'-dimethyl viologen (MV2+) and chloro-p-benzoquinone (CI-BQ) takes place with quenching rate constants (k(q)) of 8.0 x 10(6) and 1.2 x 10(6) M-1 s(-1) in methanol, respectively. A k(q) value of 2 x 10(8) M-1 s(-1) was measured for the quenching of the excited state of Rh-2(O2CCH3)(4)(PPh3)(2) by O-2 in methanol. The observations are consistent with the production of an excited state with excited-state energy, E-00, between 1.34 and 1.77 eV.