Here, we present a strategy designed to permit access to the PDI triplet manifold that preserves the desirable colorfastness and visible light-absorption properties associated with these dyes. To this end, three new Pt(II) complexes each bearing two PDI moieties tethered to the metal center via acetylide linkages emanating from one of the PDI bay positions have been synthesized, structurally characterized, and thoroughly examined by nanosecond laser flash photolysis. Upon ligation, the bright singlet-state fluorescence of the PDI chromophore is quantitatively quenched, and no long wavelength photoluminescence is observed from the Pt(II)-PDI complexes in deaerated solutions. In each of the Pt-PDI chromophores, quantitatively similar transient absorption difference spectra were obtained; the only distinguishing characteristic is in their single-exponential lifetimes (tau = 246 ns, 1.0 micros, and 710 ns). Triplet-state sensitization experiments of "free" PDI-CCH using thioxanthone confirmed the PDI triplet state assignments in each of the Pt-PDI structures.

The synthesis, structural characterization, electrochemistry, and molecular photophysics of [Ir(ppy)(2)(bpy-C[triple bond]C-Bodipy)](PF(6)), where ppy is 2-phenylpyridine and bpy-C[triple bond]C-Bodipy is 5-ethynyl-2,2'-bipyridine-8-phenyl-1,3,5,7-tetramethyl-4,4-bis(2,5-dioxaoct-7-ynyl)-4-bora-3a,4a-diaza-s-indacene (4), is presented. Static and dynamic photoluminescence and absorption measurements in conjunction with cyclic voltammetry were employed to elucidate the nature of the intramolecular energy transfer processes occurring in the excited state of the title chromophore. Parallel studies were performed on appropriate model chromophores (2 and 3) intended to represent the photophysics of the isolated molecular subunits, that is, triplet metal-to-ligand-charge-transfer ((3)MLCT) and triplet Bodipy intraligand ((3)IL) excited states, respectively. Upon charge transfer excitation of the title chromophore, the (3)MLCT based phosphorescence readily observed in 2 (Phi(em) = 0.027, tau = 243 ns) is quantitatively quenched resulting from production of the (3)Bodipy excited state through intramolecular triplet-triplet energy transfer. The formation of the (3)Bodipy-localized excited state is confirmed by features in the transient absorption difference spectrum, extended excited-state lifetime (tau = 25 micros), as well the observation of (3)IL Bodipy-based phosphorescence detected at 730 nm at 77 K. The low temperature Bodipy phosphorescence is readily produced in 4 as a result of the internal Ir(III) heavy atom.

Compounds of the type [Ru(tpy)(L2)(dmso)](z+) (tpy is 2,2':6',2' '-terpyridine; L2 can be 2,2'-bipyridine (bpy), N,N,N',N'-tetramethylethylenediamine (tmen), 2-pyridine carboxylate (pic), acetylacetonate (acac), malonate (mal), or oxalate (ox)) have been studied by X-ray crystallography, electrochemistry, NMR, IR, and UV-vis spectroscopy. When L2 is bpy, tmen, or pic, the dmso ligand can be intramolecularly isomerized either electrochemically or photochemically. Isomerization is not observed when L2 is acac, mal, or ox. Isomerization results in a drastic change in the absorption spectrum, as well as in the voltammetry. Absorption maxima shift by 3470 (419-490 nm), 4775 (421-527 nm), and 4440 cm(-)(1) (429-530 nm) for the bpy, pic, and tmen complexes, respectively. Reduction potentials for S-bonded and O-bonded complexes differ by 0.57, 0.75, and 0.62 V for the bpy, pic, and tmen complexes, respectively. Quantum yields of isomerization (phi(S)(-->)(O)) were determined for the bpy (0.024 +/- 1), pic (0.25 +/- 1), and tmen (0.007 +/- 1) complexes. In comparison of these data to photosubstitution quantum yields, it appears that the isomerization mechanism does not involve the ligand field states. This result is surprising given the importance of these states in the photochemistry of ruthenium and osmium polypyridine complexes. These results and details of the mechanism are discussed.

The homoleptic arylisocyanide tungsten complexes, W(CNXy) 6 and W(CNIph) 6 (Xy = 2,6dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400−550 nm). MLCT emission (λ max ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy) 6 and W(CNIph) 6 with lifetimes of 17 and 73 ns, respectively. Diffusioncontrolled energy transfer from electronically excited W(CNIph) 6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bu n 4 N][PF 6 ], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph) 6 ] + and [anth] •− . ET from *W to benzophenone and cobalticenium also is observed in [Bu n 4 N][PF 6 ]/THF solutions. The estimated reduction potential for the [W(CNIph) 6 ] + /*W couple is −2.8 V vs Cp 2 Fe +/0 , establishing W(CNIph) 6 as one of the most powerful photoreductants that has been generated with visible light.