Trichromophoric Systems from Square-Planar Pt-Ethynylbipyridine and Octahedral Ru- and Os-Bipyridine Centers: Syntheses, Structures, Electrochemical Behavior, and Bipartition of Energy Transfer

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+), PtRu 2, the Pt-bipyridine-acetylide/Os-bipyridine analogue, PtOs 2, 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 lambda exc = 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 lambda exc = 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 PtRu 2, PtOs 2, 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.

A Pre‐organised Truxene Platform for Phosphorescent [Ru(bpy)2] and [Os(bpy)2] Metal Centres: A Clear‐Cut Switch from Förster‐ to Dexter‐Type Energy‐Transfer Mechanism

“…The lifetime of L 1 is of the same order of magnitude of values reported for halogen‐containing truxenes,26, 27 but notably the emission quantum yield is unusually high and this results in a high k r value of 8×10 8 s −1 . The Ru and Os complexes ( RuL 1 , OsL 1 and OsL 2 ) display luminescence properties (Table 2) similar to those previously observed19 for their precursors Ru and Os (Scheme ), here reported as sake of comparison. Notably, the truxene‐containing complexes display an emission quantum yield about 40 % higher than the respective precursors Ru and Os .…”

“…Further complexation reactions with one equivalent of ruthenium(II) or osmium(II) [M II (bpy) 2 Cl 2 ] complexes afforded RuL 1 and OsL 1 , respectively. Considering the difficulty of complexing the osmium(II) cation,19 we performed the reaction by microwave assisted heating. After only one hour at 180 °C, OsL 1 could be isolated in reasonable yield (40 %).…”

Synthesis, characterization and photophysics of alkyne bridged bimetallic rhenium(I) and ruthenium(II) complexes

“…Since the energy level of MLCT state of rhenium(I) is higher than ruthenium(II), * Re(I) acts as donor and Ru(II) acts as acceptor. Similar conclusion has been reached from the lifetime and quantum yield data in the case of dyad and triad complexes involving Pt, Ru and Os [46]. The increase in lifetime and quantum yield observed in the present study can be explained as detailed below similar to the previous report.…”

Facile Synthesis of Luminescent Ir–Pt–Ir Trimetallic Complexes

“…In addition, such constructs can serve as models for understanding the long‐range excited‐state and charge transport processes found in natural photosynthesis . As such, a large number of photoactive multimetallic complexes have been prepared and studied …”