Publications (4)8.44 Total impact
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Article: Photochemical, photophysical and redox properties of novel fulgimide derivatives with attached 2,2'-bipyridine (bpy) and [M(bpy)(3)](2+) (M = Ru and Os) moieties.
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ABSTRACT: Fulgimides monosubstituted with [M(bpy)(3)](2+) (M = Ru, Os; bpy = 2,2'-bipyridine) chromophore units and with a single bpy group were synthesized and investigated as components of conceivable dinuclear photochromic switches of luminescence. The E-, Z- and closed-ring (C) photoisomer forms of the bpy-bound fulgimide were successfully separated by semi-preparative HPLC. The same procedure failed, however, in the case of the [M(bpy)(3)](2+)-substituted fulgimides. Energy transfer from the excited photochromic unit to the metal-bpy centre competes with the fulgimide cyclization, reducing the photocyclization quantum yields by approximately one order of magnitude compared to the non-complexed fulgimide-bpy ligand (phi(EC) = 0.17, phi(EZ) = 0.071, phi(ZE) = 0.15 at lambda(exc) = 334 nm). The cycloreversion of the fulgimide-bpy ligand is less efficient (phi(CE) = 0.047 at lambda(exc) = 520 nm). The intensity of the (3)MLCT-based luminescence of the metal-bpy chromophore (in MeCN, phi(deaer) = 6.6 x 10(-2) and tau(deaer) = 1.09 micros for Ru; phi(deaer) = 6.7 x 10(-3) and tau(deaer) = 62 ns for Os) is not affected by the fulgimide photoconversion. These results and supporting spectro-electrochemical data reveal that the lowest triplet excited states of the photochromic fulgimide moiety in all its E-, Z- and closed-ring forms lie above the lowest (3)MLCT levels of the attached ruthenium and osmium chromophores. The actual components are therefore unlikely to form a triad acting as functional switch of energy transfer from [Ru(bpy)(3)](2+) to [Os(bpy)(3)](2+) through the photochromic fulgimide bridge.Dalton Transactions 06/2009; · 3.84 Impact Factor -
Article: Rodlike bimetallic ruthenium and osmium complexes bridged by phenylene spacers. Synthesis, electrochemistry, and photophysics.
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ABSTRACT: In the search for light-addressable nanosized compounds we have synthesized 10 dinuclear homometallic trisbipyridyl complexes of linear structure with the general formula [M(bpy)3-BL-M(bpy)3]4+ [M = Ru(II) or Os(II); BL = polyphenylenes (2, 3, 4, or 5 units) or indenofluorene; bpy = 2,2'-bipyridine]. By using a "chemistry on the complex" approach, different sizes of rodlike systems have been obtained with a length of 19.8 and 32.5 A for the shortest and longest complex, respectively. For one of the ruthenium precursors, [Rubpy-ph2-Si(CH3)3][PF6]2, single crystals were obtained by recrystallization from methanol. Their photophysical and electrochemical properties are reported. All the compounds are luminescent both at room and low temperature with long excited-state lifetimes due to an extended delocalization. Nanosecond transient absorption showed that the lowest excited state involves the chelating unit attached to the bridging ligand. Electrochemical data indicated that the first reduction is at a slightly more positive potential than for the reference complexes [M(bpy)3]2+ (M = Ru, Os). This result confirms that the best acceptor is the bipyridine moiety connected to the conjugated spacers. The role of the tilt angle between the phenylene units, in the two series of complexes, for the ground and excited states is discussed.Inorganic Chemistry 07/2005; 44(13):4706-18. · 4.60 Impact Factor -
Article: Photochromic switches incorporated in bridging ligands: a new tool to modulate energy-transfer
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ABSTRACT: The thoughful construction of molecular switches has led to a gamut of supramolecular systems that can be used in molecular electronics. These include molecules based on thienylethenes, spiropyrans, fulgides, dithienylphenanthrolines, and diazafluorenes. This article reviews the recent developments made in the synthesis and characterization of all these systems, thereby allowing a comparative study to validate the viability of these switchable molecules on a nanoscale. Also, the drawbacks of each class are demonstrated and, at the same time, the remedies for further improvisation are prescribed. We have made an honest attempt to present an exhaustive account of all the different photochromic switches developed by us hitherto. -
Article: Photoinduced electronic energy transfer in modular, conjugated, dinuclear Ru(II)/Os(II) complexes
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ABSTRACT: Rigid, modular heterometallic dinuclear complexes containing luminescent units have been synthesized and their photophysical properties investigated. The metal complexes are derivatives of ruthenium and osmium trisbipyridine compounds and are linked by 2, 3, 4 or 5 para-phenylene units. A fast and efficient photoinduced energy transfer takes place from the excited ruthenium moiety to the osmium-based component. The rate constants of the energy transfer processes have been determined by time-resolved emission and sub-picosecond transient absorption spectroscopy. A comparison with similar systems containing substituted polyphenylene units is made in order to clarify the role of the tilt angle between the spacers on the energy transfer rates. Such investigation confirmed that a through bond Dexter type mechanism is responsible for the process.Coordination Chemistry Reviews.
