title: Light harvesting and directional energy transfer in long-lived homo- and heterotrimetallic complexes of Fe(II), Ru(II), and Os(II).
abstract: A new family of trimetallic complexes of the form [(bpy)2 M(phen-Hbzim-tpy)M'(tpy-Hbzim-phen)M(bpy)2](6+) (M=Ru(II), Os; M'=Fe(II), Ru(II), Os; bpy=2,2'-bipyridine) derived from heteroditopic phenanthroline-terpyridine bridge 2-{4-[2,6-di(pyridin-2-yl) pyridine-4-yl]phenyl}-1H-imidazole[4,5-f][1,10]phenanthroline (phen-Hbzim-tpy) were prepared and fully characterized. Zn(2+) was used to prepare mixed-metal trimetallic complexes in situ by coordinating with the free tpy site of the monometallic precursors. The complexes show intense absorptions throughout the UV/Vis region and also exhibit luminescence at room temperature. The redox behavior of the compounds is characterized by several metal-centered reversible oxidation and ligand-centered reduction processes. Steady-state and time-resolved luminescence data show that the potentially luminescent Ru(II)- and Os(II)-based triplet metal-to-ligand charge-transfer ((3)MLCT) excited states in the triads are quantitatively quenched, most likely by intercomponent energy transfer to the lower lying (3)MLCT (for Ru and Os) or triplet metal-centered ((3)MC) excited states of the Fe(II) subunit (nonluminescent). Interestingly, iron did not adversely affect the photophysics of the respective systems. This suggests that the multicomponent molecular-wire-like complexes investigated here can behave as efficient light-harvesting antennas, because all the light absorbed by the various subunits is efficiently channeled to the subunit(s) in which the lowest-energy excited states are located.
authors.affiliation: Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700032 (India).
authors.forename: Dinesh
authors.initials: D
authors.lastname: Maity
authors.forename: Chanchal
authors.initials: C
authors.lastname: Bhaumik
authors.forename: Sourav
authors.initials: S
authors.lastname: Mardanya
authors.forename: Srikanta
authors.initials: S
authors.lastname: Karmakar
authors.forename: Sujoy
authors.initials: S
authors.lastname: Baitalik
keywords: heterometallic complexes; iron; luminescence; osmium; ruthenium