• A Pt(II) complex with both a phenanthroline and a tetrathiafulvalene-extended dithiolate ligand: Synthesis, crystal structure, electro-chemical and spectroscopic properties
    C. Jia, J. Ding, S.-X. Liu, G. Labat, A. Neels, A. Hauser and S. Decurtins
    Polyhedron, 55 (2013), p87-91
    DOI:10.1016/j.poly.2013.02.064 | unige:32100 | Article HTML | Article PDF
 
The reaction of 4,5-bis(2'-cyano-ethylsulfanyl)-4',5'-dipropylthiotetrathiafulvalene with [Pt(phen)Cl2] (phen = 1,10-phenanthroline) with CsOH as base in CH3OH–THF affords the target complex 1 in 44% yield. This complex crystallizes in the monoclinic space group P21/c, M = 790.01, a = 12.1732(12), b = 15.851(2), c = 14.5371(16) Å, b = 107.693(12)˚, V = 2672.4(5) Å3 and Z = 4. It undergoes two reversible single-electron oxidation and two irreversible reduction processes. An intense electronic absorption band at 15200 cm-1 (658 nm) in CH2Cl2 is assigned to the intramolecular mixed metal/ligand-to-ligand charge transfer (LLCT) from a tetrathiafulvalene-extended dithiolate-based HOMO to a phenanthroline-based LUMO. This band shifts hypsochromically with increasing solvent polarity. Systematic changes in the optical spectra upon oxidation allow precise tuning of the oxidation states of 1 and reversible control over its optical properties. Irradiation of 1 at 15625 cm-1 (640 nm) in glassy solution below 150 K results in emission from the 3LLCT excited state.
  
In order to study the electronic interactions in donor-acceptor ensembles as a function of pH, an efficient synthetic route to three imidazole-annulated tetrathiafulvalene (TTF) derivatives 1-3 is reported. Their electronic absorption spectra, in view of photoinduced intramolecular charge transfer, and their electrochemical behavior were investigated, and pKa values for the two protonation processes on the acceptor unit were determined in organic solvents by photometric titration. The influence of the TTF moiety on these values is discussed.
  • Pronounced Electrochemical Amphotericity of a Fused Donor–Acceptor Compound: A Planar Merge of TTF with a TCNQ-Type Bithienoquinoxaline
    X. Gugano, A.L. Kanibolotsky, C. Blum, S.F.L. Mertens, S.-X. Liu, A. Neels, H. Hagemann, P.J. Skabara, S. Leutwyler, T. Wandlowski, A. Hauser and S. Decurtins
    Chemistry - A European Journal, 15 (1) (2009), p63-66
    DOI:10.1002/chem.200802011 | unige:3555 | Abstract | Article HTML | Article PDF
 
Electronic absorption spectrum of 1 in DMF solution at room temperature, together with the calculated oscillator strengths.
  
  • Ruthenium(II) Coordination Chemistry of a Fused Donor-Acceptor Ligand: Synthesis, Characterization and Photoinduced Electron Transfer Reactions of [{Ru(bpy)2}n(TTF-ppb)](PF6)2n (n = 1, 2)
    C. Goze, N. Dupont, E. Beitler, C. Leiggener, H. Jia, P. Monbaron, S.-X. Liu, A. Neels, A. Hauser and S. Decurtins
    Inorganic Chemistry, 47 (23) (2008), p11010-11017
    DOI:10.1021/ic801252t | unige:3564 | Abstract | Article HTML | Article PDF
A π-extended, redox-active bridging ligand 4′,5′-bis(propylthio)tetrathiafulvenyl[i]dipyrido[2,3-a:3′,2′-c]phenazine (L) was prepared via direct Schiff-base condensation of the corresponding diamine−tetrathiafulvalene (TTF) precursor with 4,7-phenanthroline-5,6-dione. Reactions of L with [Ru(bpy)2Cl2] afforded its stable mono- and dinuclear ruthenium(II) complexes 1 and 2. They have been fully characterized, and their photophysical and electrochemical properties are reported together with those of [Ru(bpy)2(ppb)]2+ and [Ru(bpy)2(μ-ppb)Ru(bpy)2]4+ (ppb = dipyrido[2,3-a:3′,2′-c]phenazine) for comparison. In all cases, the first excited state corresponds to an intramolecular TTF → ppb charge-transfer state. Both ruthenium(II) complexes show two strong and well-separated metal-to-ligand charge-transfer (MLCT) absorption bands, whereas the 3MLCT luminescence is strongly quenched via electron transfer from the TTF subunit. Clearly, the transient absorption spectra illustrate the role of the TTF fragment as an electron donor, which induces a triplet intraligand charge-transfer state (3ILCT) with lifetimes of approximately 200 and 50 ns for mono- and dinuclear ruthenium(II) complexes, respectively.
  • An Experimental and Computational Study on Intramolecular Charge Transfer: A Tetrathiafulvalene Fused Dipyridophenazine Molecule
    C. Jia, S.-X. Liu, C. Tanner, C. Leiggener, A. Neels, L. Sanguinet, E. Levillain, S. Leutwyler, A. Hauser and S. Decurtins
    Chemistry - A European Journal, 13 (13) (2007), p3804-3812
    DOI:10.1002/chem.200601561 | unige:3597 | Abstract | Article HTML | Article PDF
 
To study the electronic interactions in donor-acceptor (D-A) ensembles, D and A fragments are coupled in a single molecule. Specifically, a tetrathiafulvalene (TTF)-fused dipyrido[3,2-a:2',3'-c]phenazine (dppz) compound having inherent redox centers has been synthesized and structurally characterized. Its electronic absorption, fluorescence emission, photoinduced intramolecular charge transfer, and electrochemical behavior have been investigated. The observed electronic properties are explained on the basis of density functional theory.
  • Preparation and characterization of 3-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)naphthopyranone: a luminescent redox-active donor–acceptor compound
    S. Dolder, S.-X. Liu, X. Gugano, M. Atanasov, C.A. Daul, C. Leiggener, A. Hauser, A. Neels and S. Decurtins
    Tetrahedron, 62 (48) (2006), p11106-11111
    DOI:10.1016/j.tet.2006.09.032 | unige:3295 | Abstract | Article HTML | Article PDF
A new 1,3-dithiol-2-ylidene substituted naphthopyranone 2 has been synthesized and characterized. UV–vis spectroscopic and cyclic voltammetry results, interpreted on the basis of density functional theory, show that 2 displays an intramolecular charge-transfer transition and acts like a donor–acceptor (D–A) system. Furthermore, a weak fluorescence originating from the excited charge-transfer state is observed.
  • Inter- and Intramolecular Interactions in Some Supramolecular Photochemical Systems
    S. Delahaye, C. Loosli, S.-X. Liu, S. Decurtins, G. Labat, A. Neels, A. Loosli, T.R. Ward and A. Hauser
    Advanced Functional Materials, 16 (2) (2006), p286-295
    DOI:10.1002/adfm.200500329 | unige:3286 | Abstract | Article PDF
In supramolecular systems, the interaction between different units modulates their photophysical properties. a) For platinum(II) complexes with ligands that have extended π systems, π-stacking and direct metal-metal interactions result in the formation of excimers with characteristically red-shifted luminescence. Time-resolved emission spectra show clear evidence of dual luminescence. b) In phthalocyanines to which electron-donating tetrathiafulvalene (TTF) groups have been fused, the luminescence is strongly quenched by intramolecular electron transfer. The luminescence can be switched on by oxidation of the TTF groups. c) The luminescence of ruthenium tris-bipyridyl derivatives is strongly influenced by the environment. Linked to biotin, the luminescence quantum yield of such a complex is enhanced by 30 % upon binding to avidin. Furthermore, the binding to avidin induces a circular-dichroism signal from the π-π* transition of the initially racemic ruthenium tris-bipyridyl derivative.
  • Synthesis and Electrochemical and Photophysical Studies of Tetrathiafulvalene-Annulated Phthalocyanines
    C. Loosli, C. Jia, S.-X. Liu, M. Haas, M. Dias, E. Levillain, A. Neels, G. Labat, A. Hauser and S. Decurtins
    Journal of Organic Chemistry, 70 (13) (2005), p4988-4992
    DOI:10.1021/jo0501801 | unige:3274 | Abstract | Article HTML | Article PDF
The synthesis of tetrakis(tetrathiafulvalene)-annulated metal-free and metallophthalocyanines 58 via the tetramerization of the phthalonitrile derivative 4 is reported. All of them have been fully characterized by electronic absorption spectroscopy, thin-layer cyclic voltammetry, mass spectrometry, and elemental analysis. Their solution electrochemical data show two reversible four-electron oxidation waves, indicating that these fused systems are strong π-electron donors, which give rise to tetra- or octaradical cation species. For the metal-free phthalocyanine 5, additionally a reversible one-electron wave was found in the negative direction arising from the reduction of the macrocycle. Moreover, the tetrathiafulvalene unit acts as an efficient reductive electron-transfer quencher for the phthalocyanine emission, but upon its oxidation, an intense luminescence is switched on.

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