EXCITED-STATE ABSORPTION-SPECTRA OF THE TETRANUCLEAR CUPROUS IODIDE CLUSTER CU4I4(PY)(4) AND RELATED SPECIES

Nanosecond flash photolysis studies have been carried out on the tetra meric clusters Cu(4)I(4)L(4) (L = pyridine (Py), 4-t-butyl pyridine (4 -Bu(t)-py)), 4-phenyl pyridine (Phpy) or piperidine (pip)). A broad tr ansient absorption band in the visible region was observed for each of the clusters with aromatic heterocycle ligands upon excitation at 337 or 355 nm but no excited state absorption (ESA) was observed when L i s the saturated amine piperidine. The ESA band maxima are dependent up on the nature of the pyridine ring substituent, occurring at 542 nm, 5 65 nm, and 532 nm for L = py, Phpy, and 4-Bu(t)-py), respectively. The se ESA bands are modestly solvent-sensitive, shifting to lower energy in solvents of lower polarity. The microsecond lifetimes of the ESA ba nds are comparable to those observed for emission from the triplet clu ster centered excited states ((CC)-C-3) previously assigned for these compounds (K.R. Kyle, C.K. Ryu, J.A. DiBenedetto and P.C. Ford, J. Am. Chem. Sec., 113 (1991) 2954-2965). Consideration of this data and exa mination of the energetics of the states involved suggests that the tr ansition responsible for the excited state absorption occurs from the 3CC state to a higher energy triplet halide-to-ligand charge transfer ((3)XLCT) state.