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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.

Tight contact ion pairs of general formula {Pt(H(2)-R(2)-dto)(2)(2+),(X(-))(2)} have been prepared, and their absorption spectra and luminescence properties (at room temperature in dichloromethane fluid solution and at 77 K in butyronitrile rigid matrix) have been studied (dto = dithiooxamide; R = methyl, X = Cl (1); R = butyl, X = Cl (2); R = benzyl, X = Cl (3); R = cyclohexyl, X = Cl (4); R = cyclohexyl, X = Br (5); R = cyclohexyl, X = I (6)). The absorption spectra of all the compounds are dominated by moderately strong Pt(dpi)/S(p) to dithiooxamide (pi) charge transfer (Pt/S --> dto CT) bands in the visible region (epsilon in the 10(4)-10(5) M(-)(1) cm(-)(1) range). Absorption features are also present at higher energies, due to pi-pi transitions centered in the dto ligands (ligand centered, LC). All the compounds exhibit a unstructured luminescence band in fluid solution at room temperature, with the maximum centered in the 700-730 nm range. The luminescence bands are blue-shifted about 4000 cm(-)(1) on passing to the rigid matrix at 77 K. Luminescence lifetimes are on the 10(-)(8)-10(-)(7) s time scale at room temperature and 1 order of magnitude longer at 77 K. Luminescence is assigned to triplet Pt/S --> dto CT excited states in all cases. Compounds 3-6 also exhibit a second higher-energy luminescence band at room temperature, centered at about 610 nm, attributed to a LC excited state. Charge transfer interactions between halides and dto ligands destabilize dto-centered orbitals, affecting the energy of Pt/S --> dto CT transitions and states. The X counterions and X --> dto CT levels are proposed to play a role in promoting excited state conversion between LC and Pt/S --> dto CT levels. The R substituents on the nitrogen atoms of the dto ligands influence the absorption and photophysical properties of the compounds, by affecting proximity of the ion pairs. The possibility to functionalize the R substituents may open the way to interface these luminescent compounds with desired substrates and to construct supramolecular assemblies.

The title compound, C(21)H(19)N(7), is a polypyridine ligand that is suitable for assembling complex metal systems capable of photoinduced electron transfer. The solid-state structure has been determined at room temperature by single-crystal X-ray diffraction. The molecule is not flat and both the bis(pyridyl)triazole and the benzylideneamine fragments show significant distortions from planarity.

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