Treelike (dendritic) structures made of Ru"-polypyridine complexes have been prepared by the "complexes-asmetals and complexes-as-ligands" synthetic strategy. The key building blocks are Ru" complexes of the 2,3-bis-(2-pyridy1)pyrazine (2.3-dpp) bridging ligand, where one of the two chelating sites can be protected by methylation. Dendendrimers exhibit strong absorption in the UV/Vis spectral region, a moderately strong red luminescence, and a great number of metal-based oxidation and ligandde de drimers containing four, ten, and twentytwo metal ions have been obtained. These SJISlreffts based reduction processes. The nature of the terminal ligands determines in which subunits of the supramolecular array the HOMO and LUMO orbitals and the luminescent excited state are localized. The reported synthetic strategy is eflicient, characterized by a full, step-by-step control of the growth process, and can be easily extended to building blocks containing other metals and/or ligands.
Two new cyclometalated Rh(III) and Ir(III) complexes have been synthesized, and their absorption spectra, luminescence properties (in rigid matrix at 77 K and in fluid solution at room temperature), and electrochemical behavior have been investigated and compared to those of other similar Rh(HI) and Ir(III) cyclometalated species.The new compounds are [Rh(ppy)2(dpt-NH2)](PF6) (1) and [Ir(ppy)2(dpt-NH2)](PF6) (2) (ppy = phenylpyridine anion; dpt-NH2 = 4-amino-3,5-bis(2-pyridyl)-4/f-l,2,4-triazole). The absorption spectra of the compounds are dominated by intense ligand-centered bands in the UV region (ema* in the range 10* 1234-105 M-1 cm-1) and by moderately intense metal-to-ligand charge transfer bands in the visible region (emax in the range 103 7-104 M-1 cm-1). A reversible oxidation occurs for 2 at +1.23 V vr SCE, assigned to removal of an electron from a metalcentered cbr orbital, while an irreversible oxidation is observed for 1 at more positive potentials (Epeak = +1.51 V vr SCE), assigned to removal of an electron from a metal-ligand (C-) a-bonding orbital. Both complexes are luminescent in rigid matrices at 77 K (1, Am* = 458 nm, r = 160 fis; 2, Amax = 475 nm, r = 5.8 fis), while only the Ir compound emits in fluid solution at room temperature (Ama* = 560 nm, r = 870 ns, = 0.246). The emission originates from a metal-perturbed, triplet ppy-centered excited state for the Rh species, while a triplet MLCT level is responsible for the emission of the Ir compound. The results obtained are a step toward the preparation of photoactive and redox-active multinuclear compounds based on bis(pyridyl)triazole derivative bridges and incorporating Ir(IH) and Rh(III) cyclometalated building blocks.
Dendrimers based on Ru(II) and Os(II) polypyridine complexes as building blocks and 2,3-dpp (2,3-dpp = 2,3-bis(2'pyridyl)pyrazine) as bridging ligands are presented and their properties as light-harvesting antenna systems are illustrated. The dendrimers exhibit a huge absorption in the visible region and energy migration patterns whose direction and efficiency depend on the synthetically determined topography of the systems. New recent developments are also discussed, with particular regard towards ultrafast energy transfer processes and long-range electron transfer within the dendritic arrays.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.