Platinum diimine bis(acetylide) complexes: synthesis, characterization, and luminescence properties

A new set of luminescent platinum(II) diimine complexes has been synthesized and characterized. The anionic ligands in these complexes are arylacetylides. The complexes are brightly emissive in fluid solution with relative emission quantum yields phiem ranging from 3 x 10(-3) to 10(-1). Two series of complexes have been investigated. The first has the formula Pt(Rphen)(C...CC6H5)2 where Rphen is 1,10-phenanthroline substituted in the 5-position with R = H, Me, Cl, Br, NO2, or C...CC6H5, while the second has the formula Pt(dbbpy)(C=CC6H4X)2 where dbbpy = 4,4'-di(tert-butyl)bipyridine and X = H, Me, F, or NO2. From NMR, IR, and electronic spectroscopies, all of the complexes are assigned a square planar coordination geometry with cis-alkynyl ligands. The crystal structure of Pt(phen)(Ce-CC6H4CH3)2 confirms this assignment. All of the complexes exhibit an absorption band at ca. 400 nm that corresponds to a Pt d-->pi*diimine charge-transfer transition. The variation of lambdamax for this band with substituent variation supports this assignment. From similar changes in the energy of the solution luminescence as a function of substituents R and X, the emissive excited state is also of MLCT origin, but with spin-forbidden character on the basis of excited-state lifetime measurements (0.01-5.6 micros). The complexes undergo electron-transfer quenching, showing good Stern-Volmer behavior using 10-methylphenothiazine and N,N,N',N'-tetramethylbenzidine as reductive quenchers. Excited-state reduction potentials are estimated on the basis of a simple thermochemical analysis. Crystal data for Pt(phen)(C...CC6H4CH3)2: monoclinic, space group C2/c, a = 19.0961(1) A, b = 10.4498(1) A, c = 11.8124(2) A, beta = 108.413(1) degrees, V = 2236.49 A3, number of reflections 1614, number of variables 150, R1 = 0.0163, wR2 (I > 2sigma) = 0.0410.     

Preparation of block copolymer vesicles in solution

Block copolymer vesicles can be prepared in solution from a variety of different amphiphilic systems. Polystyrene‐block‐poly(acrylic acid), polystyrene‐block‐poly(ethylene oxide), and many other block copolymer systems can produce vesicles of a wide range of sizes; those in the range of 100–1000 nm have been explored extensively. Different factors, such as the absolute and relative block lengths, the presence of additives (ions, homopolymers, and surfactants), the water content in the solvent mixture, the nature and composition of the solvent, the temperature, and the polydispersity of the hydrophilic block, provide control over the types of vesicles produced. Their high stability, resistance to many external stimuli, and ability to package both hydrophilic and hydrophobic compounds make them excellent candidates for use in the medical, pharmaceutical, and environmental fields. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 923–938, 2004     

Platinum chromophore-based systems for photoinduced charge separation: a molecular design approach for artificial photosynthesis

Photoinduced charge separation is a fundamental step in photochemical energy conversion. In the design of molecularly based systems for light-to-chemical energy conversion, this step is studied through the construction of two- and three-component systems (dyads and triads) having suitable electron donor and acceptor moieties placed at specific positions on a charge-transfer chromophore. The most extensively studied chromophores in this regard are ruthenium(II) tris(diimine) systems with a common 3MLCT excited state, as well as related ruthenium(II) bis(terpyridyl) systems. This Forum contribution focuses on dyads and triads of an alternative chromophore, namely, platinum(II) di- and triimine systems having acetylide ligands. These d8 chromophores all possess a 3MLCT excited state in which the lowest unoccupied molecular orbital is a pi orbital on the heterocyclic aromatic ligand. The excited-state energies of these Pt(II) chromophores are generally higher than those found for the ruthenium(II) tris(diimine) systems, and the directionality of the charge transfer is more certain. The first platinum diimine bis(arylacetylide) triad, constructed by attaching phenothiazene donors to the arylacetylide ligands and a nitrophenyl acceptor to 5-ethynylphenanthroline of the chromophore, exhibited a charge-separated state of 75-ns duration. The first Pt(tpy)(arylacetylide)+-based triad contains a trimethoxybenzamide donor and a pyridinium acceptor and has been structurally characterized. The triad has an edge-to-edge separation between donor and acceptor fragments of 27.95 Angstroms. However, while quenching of the emission is complete for this system, transient absorption (TA) studies reveal that charge transfer does not move onto the pyridinium acceptor. A new set of triads described in detail here and having the formula [Pt(NO2phtpy)(p-C triple-bond C-C6H4CH2(PTZ-R)](PF6), where NO2phtpy = 4'-{4-[2-(4-nitrophenyl)vinyl]phenyl}-2,2';6',2'-terpyridine and PTZ = phenothiazine with R = H, OMe, possess an unsaturated linkage between the chromophore and a nitrophenyl acceptor. While the parent chromophore [Pt(ttpy)(C triple-bond CC6H5)]PF6 is brightly luminescent in a fluid solution at 298 K, the triads exhibit complete quenching of the emission, as do the related donor-chromophore (D-C) dyads. Electrochemically, the triads and D-C dyads exhibit a quasi-reversible oxidation wave corresponding to the PTZ ligand, while the R = H triad and related C-A dyad display a facile quasi-reversible reduction assignable to the acceptor. TA spectroscopy shows that one of the triads possesses a long-lived charge-separated state of approximately 230 ns.     

Measurement theory in the Lax-Phillips formalism

It is shown that the application of the Lax-Phillips scattering theory to quantum mechanics provides a natural framework for the realization of the ideas of the Many-Hilbert-Space theory of Machida and Namiki to describe the development of decoherence in the process of measurement. We show that if the quantum mechanical evolution is pointwise in time, then decoherence occurs only if the Hamiltonian is time-dependent. If the evolution is not pointwise in time (as in Liouville space), then the decoherence may occur even for closed systems. These conclusions apply as well to the general problem of mixing of states.     

Sulfonated polypropylene ionomers

Polypropylene ionomers have been prepared by sulfonation of copolymers of propene and 7 methyl, 1-6 octadiene, followed by neutralization to cesium salts. Both WAXS and SAXS were used to study the morphology of the samples, while their thermal properties were studied by DSC and their mechanical properties by DMTA. The sulfonation process is shown to cause a further drop in crystallinity in addition to the effect of comonomer incorporation. Ion clustering is observed when the extent of sulfonation is high enough, the limit being dependent on the copolymer composition. The ion pairs which are not incorporated into the cluster cause a small-angle upturn in the WAXS pattern. The mechanical properties are strongly affected by the drop in crystallinity, but may be partly recovered due to ion clustering. No disruption of the ion clusters is observed before thermal decomposition of the polymer.     

Polynomials: a theme which should not be forgotten

There is a definite movement to remove many of the topics concerning polynomials from the school curriculum. The purpose of this paper is to point out why this movement is misguided and should be reversed.