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 hybrid [Pt((t)Bu(3)terpy)(C[triple bond]C-Ph-C(60))](+) complex (Pt-Fu) wherein a phosphorescent platinum center is linked to fullerene has been prepared using a copper(I)-promoted cross-coupling reaction. The electrochemical and spectroscopic properties were understood in light of the properties of the isolated building blocks and references compounds, Pt and Fu. In particular, in Pt-Fu, the electrochemical studies revealed that the first reduction process is fullerene-based and that the lowest-energy Pt(+)-Fu(-) charge-separated (CS) state lies in the range 2.0-2.1 eV. The luminescence properties of the investigated species have been monitored in a CH(2)Cl(2) solvent at room temperature and in a MeOH/EtOH (1:4 v/v) glassy solution at 77 K. Upon excitation at 450 nm at room temperature and in air-free solvent, Pt displays an intense luminescence of (3)MLCT nature, with lambda(max) = 605 nm (523 nm at 77 K, corresponding to 2.37 eV), phi(em) = 0.013, and tau(em) = 920 ns. Under the same conditions, Fu exhibits the typical (1)C(60) fluorescence, with lambda(max) = 708 nm (703 nm at 77 K, corresponding to 1.76 eV), phi(em) = 6.0 x 10(-4), and tau(em) = 1.2 ns. For Pt-Fu, room-temperature excitation at 450 nm yields Pt*- and Fu*-centered excited states in a 1.2:1 proportion. However, no Pt-based emission is observed, and (i) in an air-free solvent, (1)Fu fluorescence is observed, while (ii) in an air-equilibrated solvent, singlet oxygen sensitization by the (3)Fu level takes place. Very close (1)O(2)* fluorescence intensities are observed at 1278 nm for isoabsorbing solutions at 450 nm of Fu and Pt-Fu, consistent with complete Pt --> Fu energy transfer in the dyad. The room-temperature nanosecond transient absorption spectra for Pt-Fu and Fu exhibit peaks at 680 and 690 nm with tau(TA) = 14.3 and 24.8 micros, respectively; in both cases, these are attributed to absorption by the fullerene triplet. By contrast, no CS species, Pt(+)-Fu(-), are detected. The Pt --> Fu energy transfer is discussed, and the rate constant for the (3)Pt-Fu --> Pt-(1)Fu step is evaluated, k(en) > 10(7) s(-1).

In bi- and trimetallic Pt-bipyridine-acetylide/Ru-bipyridine complexes the intermetallic Pt-Ru distance is approximately 9 è, and complete Pt-->Ru energy transfer is observed with sensitization of the Ru-based luminescence.

Various combinations of mono-or diethynyl-substituted fluorene or carbazole building blocks were connected via a r-bonded ethynyl linkage to ortho-metallated Pt(II) fragments, giving rise to phosphorescent mono-and dinuclear complexes for which the solubility and extent of delocalization could be tuned by the chemistry on the acidic methylene position of the fluorene.

This paper describes expeditious stepwise synthesis of polynuclear complexes based on heteroleptic iridium(iii) and osmium(ii) fragments linked to a central Pt(ii) module via a spirobifluorene-bridge using a strategy based on the construction of preformed complexes. The luminescence features of the final multi-chromophoric array, i.e. a tetrad consisting of spirobifluorene-bridged Pt, Ir and Os complexes, have been studied by comparison with the features of reference complexes bearing two identical luminophores (Ir or Os) at the periphery. The (3)MPtLCT and (3)LC states of the Pt and spiro ligand undergo fast energy transfer into the (3)MIrLCT or the (3)MOsLCT state in the Pt-M2 (M = Ir or Os) arrays, whereas the (3)LC and the (3)MPtLCT states function as energy reservoirs for the metal excited states close in energy, resulting in a pronounced increase of the excited state lifetimes of these arrays. The tetrad efficiently works as an antenna system where the collected light energy is transferred to the Os unit acting as the final collector.

The synthesis, characterization, photophysics, and time-dependent density functional theory (TD-DFT) calculations of spirobifluorene-bipyridine based iridium(III), osmium(II), and mixed Ir/Os complexes are presented. The preparation of the reference and mixed complexes proceeded step-by-step and microwave irradiation facilitated the complexation of osmium. The absorption of the target heterobimetallic derivative, Ir-L-Os, is described by linear combination of half of the absorption spectra of the homobimetallic analogues, Ir-L-Ir and Os-L-Os, due to the occurrence of mixed ligand and metal based transitions when the spirobifluorene-(bpy)(2) bridging ligand L is linked to the metal, confirming a negligible interaction between the substituted metallic chromophores. TD-DFT calculations on monometallic, homo- and hetero-bimetallic complexes fully disentangled the origin of the absorption features. Noticeably, in the mixed Ir-L-Os complex an almost quantitative energy transfer from the (3)Ir to the (3)Os MLCT state is occurring, with a rate constant of 4.1 × 10(8) s(-1) and nearly exclusively via a Dexter-type mechanism mediated by the orbitals of the spiroconjugated ligand. This result, together with the outcomes of the TD-DFT calculations, supports the existence of spiroconjugation and evidences the interesting role of this kind of bridge in the energy transfer dynamics of the arrays. In all the complexes, moreover, the ligand fluorescence is heavily quenched by energy transfer processes toward the metallic appended units; the rate constant is estimated in the order of 10(10) s(-1) for Ir-L-Os and higher than 10(12) s(-1) for the other complexes. In the heterometallic array, both at room temperature and at 77 K, all photons are thus funneled to the emissive Os (3)MLCT state, which acts as energy trap for the antenna cascade.