| Abstract
| - The synthetic approach, electrochemical behavior, and optical absorption and emission properties are reported of the Pt-bipyridine-acetylide/Ru-bipyridine complex [(dbbpy)Pt{(ebpy)Ru(bpy)2}2]4+, PtRu2, the Pt-bipyridine-acetylide/Os-bipyridine analogue, PtOs2, and the Pt/Ru/Os complex [(dbbpy)Pt(ebpy)2Ru(bpy)2Os(bpy)2]4+, PtRuOs; ebpy is 5-ethynylbpy, dbbpy is 4,4′-ditertiobutylbpy, and bpy is 2,2′-bipyridine. These triads are investigated in acetonitrile solvent by comparing their electrochemical and spectroscopic properties with those of the mononuclear species [(dbbpy)Pt(ebpy)2], Pt, [Ru(ebpy)(bpy)2]2+, Ru, and [Os(ebpy)(bpy)2]2+, Os. Results of X-ray analysis of Pt are reported, which show the planar arrangement of this unit that features two free bpy sites. The absorption spectra of the triads and the mononuclear species show that light at 452 or 376 nm can be employed to observe luminescence spectra of these complexes; for the observation of emission lifetimes, nanoled sources at 465 and 373 nm are employed. With λexc = 452 (and 465) nm, one selectively produces Ru → bpy/ebpy CT (RuLCT) or Os → bpy/ebpy CT states (OsLCT); MLCT is a metal-to-ligand charge-transfer. With λexc = 376 (and 373) nm, one populates Pt → dbbpy CT and intraligand charge transfer (ILCT, involving the ebpy fragment) levels, in addition to Ru(II)- or Os(II)-centered excited states, in aliquots that are estimated from comparison of the absorption features of the components. Upon excitation with light at 376 (and 373) nm, the optical studies of PtRu2, PtOs2, and PtRuOs reveal full quenching of the Pt-based emission and occurrence of efficient photoinduced energy transfer, leading to exclusive MLCT emission from the ruthenium and osmium centers. In particular, PtRuOs is found to exhibit a Ru- and Os-based dual luminescence, whose intensities ratio is consistent with a Pt → Os intramolecular energy transfer step being 3−6 times faster than the Pt → Ru one.
- Mixed-metal Pt−bipyridine−acetylide/Ru- and Os−bipyridine complexes have been synthesized and characterized: in the mixed-metal Pt/Ru/Os complex, through a bipartition of energy transfer both the Ru and Os centers luminesce with the latter collecting the majority of the excitation energy at 376 nm.
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