Structural and photophysical properties of [(CO)3(phen) Re(μ-Br)Re(phen)(CO)3]+[(CO)3+[Re(μ-Br)3Re(CO)3]-: Where does its luminescence come from?

The multimetallic complex [[(CO)(3)(phen) Re(mu-Br)Re(phen)(CO)(3)][(CO)(3)[Re(mu-Br)(3)Re(CO)(3)]]center dot CH2Cl2 was prepared by direct reaction of (Re(CO)(3)(THF)Br)(2) (THF: tetrahydrofuran) and 1,10-phenanthroline in a 1:1 ratio, followed by recrystallization in dichloromethane. The compound is an ionic salt where both, cation and anion, are bimetallic complexes. Inside both of them the Re-I centers are bridged by one or three bromides respectively. The compound has an absorption band centered at 375 nm in CH2Cl2, which has been assigned to a MLCT band. Excitation at 375 nm produces luminescent emission at 608 nm. Comparison of these results with closely related rhenium complexes, in addition to Time Dependant-DFT analysis, allow us to propose the [(CO)(3)(phen)Re(g-Br)Re(phen)(CO)(3)](+) cation as main responsible for luminescence. Luminescence lifetime and singlet oxygen formation quantum yield suggest also that the emissive excited state has a triplet character. (C) 2015 Elsevier Ltd. All rights reserved.