A. d'Aleo

Metal Ion Enhanced Charge Transfer in a Terpyridine-bis-Pyrene System

The synthesis, electrochemical and photophysical properties of a branched molecule 3,5-bis(pyrene-1-yl)-4′-phenyl-2,2′:6′,2″-terpyridine are reported. Spectroscopy in different solvents reveals that an optical electron transfer from the pyrene donor to the terpyridyl electron acceptor can occur in polar media, as the system displays both charge transfer (CT) absorption and CT emission. Furthermore, the study of the zinc complex as well as the bis-protonated form shows an enhancement of the electron transfer character of the system, by an increase of the acceptor strength. This is accompanied by a large increase of the non-radiative processes. With sub-nanosecond transient absorption spectroscopy, the CT state, consisting of the pyrene radical cation and the terpyridine radical anion, has been detected. At room temperature, the study of the nanosecond transient absorption spectra reveals the formation of a low-lying triplet excited state that we attribute to the pyrene moiety through which the CT state decays. At 77K, the absence of the terpyridine triplet emission also suggests the population of a low-lying triplet state of the pyrene unit.

Extending excited-state lifetimes by interchromophoric triplet-state equilibration in a pyrene-Ru(II)diimine dyad system

The synthesis and the spectroscopic properties of a bichromophoric ruthenium trisbipyridyl-1,4-diethynylenebenzene-pyrene system (Ru-b-Py) and the corresponding pyrene ligand (b-Py) are reported. The ruthenium model systems Ru-b-OH, Ru-b-Ph are also presented. UV–Vis absorption and emission at room and low temperature and time-resolved spectroscopy are discussed. For the Ru-b-Py dyad, a mixing of the 3MLCT state of the ruthenium-based component and the triplet state of pyrene, 3Py, is observed. Time-resolved transient absorption studies performed on the Ru-b-Py and on the b-Py ligand show that the lowest energy absorption is due to the population of the triplet state localized on the pyrene-component. Time-resolved studies also evidenced a relatively slow forward triplet equilibration rate, in the order of 2×105u2009s-1 (5u2009μs), and an even slower back energy transfer rate, 3.3×104u2009s-1, still faster than the intrinsic decay time of the pyrene (200u2009μs).

Electronic Energy Transfer in Dinuclear Metal Complexes Containing Meta Substituted Phenylene Units

The synthesis and photophysical properties of heterometallic dinuclear complexes based on ruthenium and osmium trisbipyridine units, Ru-mPh3-Os and Ru-mPh5-Os, in which the metal complexes are linked via an oligophenylene bridge centrally connected in the meta position, are described. Electronic energy transfer from the excited ruthenium-based component (donor) to the osmium moiety (acceptor) has been investigated using steady-state and time-resolved spectroscopy. The results obtained for the meta-substituted compounds are compared with the analogous systems in which the phenylene spacers are substituted in the para position. The mechanism of energy transfer is discussed.

Electrochemical and Photophysical Properties of Ruthenium(II) Bipyridyl Complexes with Pendant Alkanethiol Chains in Solution and Anchored to Metal Surfaces

Luminescent ruthenium trisbipyridine complexes containing one or two mercapto-alkyl chain(s) on one of the bipyridyl units have been synthesized through a new strategy. The electrochemical and photophysical properties, determined in solution and in the solid state were compared. Deposition on electrode surfaces (gold, platinum and indium tin oxide) was realized by self-assembly and the re- sulting adsorbed layers were characterized by electrochemistry and fluorescence confocal microscopy. Voltammetric measurements of the films, in aqueous and in acetonitrile solution, allowed the determination of the surface coverages and the oxidation potentials of the complexes. The effect of the number of chains and the chain length in the complexes is highlighted. Emission of the adsorbed complexes was strongly quenched by the metallic surfaces, while confocal microscopy images showed aggregate formation on am length scale. The latter results provide considerable insight into the nature of the adsorbed layers and support deductions from the voltammetric data.

Chapter 1 Self-Organised Nanoparticle Assemblies: A Panoply of Patterns

Abstract An overview of self-organisation in an archetypal nanostructured system—2D nanoparticle assemblies—is given. We first focus on the parallels that may be drawn for pattern formation in nanoscopic, microscopic, and macroscopic systems (spanning, for example, nanoparticle arrays, phase-separated polymers, diatom microskeletons, and binary fluid separation) before discussing the quantification of morphology and topology in nanostructured matter. The question of quantification is of key importance for the development of programmable or directed assembly and we highlight the central role that image morphometry can play in the software control of matter. The nanostructured systems we describe are, in very many cases, far from their ground state and we show that Monte Carlo simulations (based on the approach pioneered by Rabani et al . [ Nature 426 (2003) 271]) provide important insights into the coarsening ( i.e. approach to equilibrium) of nanoparticle arrays. We conclude with a consideration of the near-term prospects for programmable matter.

Packing effects in 4,4'-bis(4-hydroxybutyl)-2,2'-bipyridine and 4,4'-bis(4-bromobutyl)-2,2'-bipyridine.

Structure analyses of 4,4-bis(4-hydroxybutyl)-2,2-bipyridine, C18H24N2O2, (I), and 4,4-bis(4-bromobutyl)-2,2-bipyridine, C18H22Br2N2, (II), reveal intermolecular hydrogen bonding in both compounds. For (I), O-H...N intermolecular hydrogen bonding leads to the formation of an infinite two-dimensional polymer, and pi stacking interactions are also observed. For (II), C-H...N intermolecular hydrogen bonding leads to the formation of a zigzag polymer. The two compounds crystallize in different crystal systems, but both molecules possess Ci symmetry, with one half molecule in the asymmetric unit.