Excited state properties of (acetylacetonato)dicarbonyliridium(I)

Monomeric Ir(CO)2acac as it occurs in dilute solutions (<10−3 M) absorbs only in the UV spectral region and shows a greenish luminescence (λmax = 480 nm) which originates from the lowest-energy intraligand (acac) triplet. At higher concentrations a yellow coloration is observed which is attributed to the formation of oligomers. At 77 K these solutions turn blue owing to the presence of oligomers which are characterized by strong metal–metal interactions. These blue oligomers display an intense red luminescence which consists of a fluorescence at λmax = 662 nm and a phosphorescence at λmax = 815 nm.