Photophysical Properties of Hexanuclear Copper(I) and Silver(I) Clusters

The spectroscopic properties, including emission spectra and lifetimes, absorption and diffuse reflectance spectra and excitation spectra, of the hexanuclear copper(I) and silver(I) clusters Cu6(mtc)6 (1), Ag6(mtc) (2), and Ag6(dtc)6 (3) (mtc = di-n-propylmonothiocarbamate, dtc = di-n-propyldithiocarbamate) are reported. At room temperature 1 exhibits a strong single emission (e.g., in toluene λem max = 725 nm, τ = 1.0 μs) , while at 77 K each of these is a bright emitter (spectral properties: 1 in toluene, λem max = 762 nm, τ = 20 μs; 2 in toluene, λem max = 607 nm, τ = 131 μs; 3 in toluene, λem max = 550 nm, τ = 21 μs). In analogy to previous assignments in tetranuclear Cu(I) clusters, the emission bands in the octahedral (MI)6 clusters are assigned to spin-forbidden transitions from triplet excited states which are mixed d -> s and LMCT (ligand to metal charge transfer) in character modified by metal-metal interactions