• Triplet state CPL active helicene-dithiolene platinum bipyridine complexes
    T. Biet, T. Cauchy, Q. Sun, J. Ding, A. Hauser, P. Oulevey, T. Bürgi, D. Jacquemin, N. Vanthuyne, J. Crassous and N. Avarvari
    Chemical Communications, 53 (66) (2017), p9210-9213
    DOI:10.1039/C7CC05198K | unige:96312 | Abstract | Article HTML | Article PDF | Supporting Info
Chiral metal dithiolene complexes represent a family of chiral precursors, which can give rise to molecular materials with properties resulting from the interplay of chirality with conductivity, magnetism, and photophysics. We describe herein the first examples of chiral metal diimine dithiolene complexes, by the use of a platinum(II) centre coordinated by 2,2’-bipyridine and helicene-dithiolene ligands. Straightforward synthesis of racemic and enantiopure complexes allows the preparation of luminescent Pt(bipy) [4] and [6]helicene compounds for which the solid-state structure was determined as well. TD-DFT calculations support the assignment of the low energy bands observed in the UV-vis absorption spectra as mixed metal-ligand-to-ligand charge transfer transitions and confirm that the emission band results from the T1 excited state. Interestingly the enantiopure [6]helicene complexes show CPL activity at room temperature in acetonitrile solutions with anisotropy factors of 3×10-4.
Introduction of heterocycles in the helical skeleton of helicenes allows modulation of their redox, chiroptical and photophysical properties. Herein, we describe the straightforward preparation and structural characterization by single crystal X-ray diffraction of thiadiazole-[7]helicene, which has been resolved into (M) and (P) enantiomers by chiral HPLC, together with its S-shaped double [4]helicene isomer, as well as the smaller congeners thiadiazole-[5]helicene and benzothiadiazole-anthracene. A copper(II) complex with two thiadiazole-[5]helicene ligands has been structurally characterized and it shows the presence of both (M) and (P) isomers coordinated to the metal centre. The emission properties of the unprecedented heterohelicenes are highly dependent on the helical turn, as the [7]- and [5]helicene are poorly emissive, whereas their isomers, that is, the S-shaped double [4]helicene and thiadiazole-benzanthracene, are luminescent, with quantum efficiencies of 5.4% and 6.5%, respectively. DFT calculations suggest a quenching of the luminescence of enantiopure [7]helicenes through an intersystem crossing mechanism arising from the relaxed excited S1 state.
  • Structural, Photophysical and Magnetic Properties of Transition Metal Complexes Based on the Dipicolylamino-chloro-1,2,4,5-tetrazine Ligand
    I. Nazarenko, F. Pop, Q. Sun, A. Hauser, F. Lloret, M. Julve, A. El-Ghayoury and N. Avarvari
    Dalton Transactions, 44 (19) (2015), p8855-8866
    DOI:10.1039/c5dt00550g | unige:72655 | Abstract | Article HTML | Article PDF | Supporting Info
The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) 1, prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl2]2, with M = Zn(II) 2a, Cd(II) 2b, Mn(II) 2c and Co(II) 2d, when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [MII-(m-Cl)2MII] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geometries. Moreover, the chlorine atoms, either coordinated to the metal or as substituent on the tetrazine ring, engage respectively in specific anion-p intramolecular and intermolecular interactions with the electron poor tetrazine units in the solid state, thus controlling the supramolecular architecture. Modulation of the emission properties is observed in the case of the Zn(II) and Cd(II) complexes when compared to the free ligand. A striking difference is observed in the magnetic properties of the Mn(II) and Co(II) complexes. An antiferromagnetic coupling takes place in the dimanganese(II) compound (J = -1.25 cm-1) while the Co(II) centers are ferromagnetically coupled in the corresponding complex (J = +0.55 cm-1), the spin Hamiltonian being defined as H = -JSA.SB.
Bis(thiomethyl)- and bis(thiohexyl)-tetrathiafulvalene-bromo-benzothiadiazoles, containing electron donor tetrathiafulvalene (TTF) and electron acceptor benzothiadiazole (BTD) units, have been prepared by Stille coupling reactions between the TTF-SnMe3 precursors and BTD-Br2. In another series of experiments, TTF-acetylene-BTD compounds have been synthesized by Sonogashira coupling between either TTF-acetylenes and BTD-Br2 in low yields, or TTF-iodine and BTD-acetylene in moderate yields. In the compound TTF-C≡C-BTD the TTF and BTD units are coplanar in the solid state, as shown by the single crystal X-ray structure, and there is segregation in the packing between the donor and acceptor units. All the derivatives have good electron donor properties, as determined by cyclic voltammetry measurements, and they can also be reversibly reduced thanks to the presence of the BTD moiety. UV-visible spectroscopy and photophysical investigations show the presence of an intramolecular charge transfer (ICT) band and an emission band originating from the charge transfer. Both the absorption and the emission are modulated by the substitution scheme and the insertion of the acetylenic bridge.
  • Tetrathiafulvalene-1,3,5-triazines as (Multi)Donor-Acceptor Systems with Tunable Charge Transfer: Structural, Photophysical, and Theoretical Investigations
    F. Pop, F. Riobé, S. Seifert, T. Cauchy, J. Ding, N. Dupont, A. Hauser, M. Koch and N. Avarvari
    Inorganic Chemistry, 52 (9) (2013), p5023-5034
    DOI:10.1021/ic3027336 | unige:27865 | Abstract | Article HTML | Article PDF
Palladium-catalyzed cross-coupling reactions between chlorinated 1,3,5-triazines (TZ) and tetrathiafulvalene (TTF) trimethyltin derivatives afford mono- and C3 symmetric tris(TTF)-triazines as donor–acceptor compounds in which the intramolecular charge transfer (ICT) is modulated by the substitution scheme on TTF and TZ and by chemical or electrochemical oxidation. The TTF-TZ-Cl2 and (SMe)2TTF-TZ-Cl2 derivatives show fully planar structures in the solid state as a consequence of the conjugation between the two units. Electrochemical and photophysical investigations, supported by theoretical calculations, clearly demonstrate that the lowest excited state can be ascribed to the intramolecular charge transfer (ICT) π(TTF)→π*(TZ) transition. The tris(TTF) compound [(SMe)2TTF]3-TZ shows fluorescence when excited in the ICT band, and the emission is quenched upon oxidation. The radical cations TTF+• are easily observed in all of the cases through chemical and electrochemical oxidation by steady-state absorption experiments. In the case of [(SMe)2TTF]3-TZ, a low energy band at 5000 cm–1, corresponding to a coupling between TTF+• and TTF units, is observed. A crystalline radical cation salt with the TTF-TZ-Cl2 donor and PF6– anion, prepared by electrocrystallization, is described.
  • Tetrathiafulvalene-s-tetrazine: versatile platform for donor-acceptor systems and multifunctional ligands
    F. Pop, J. Ding, L.M. Lawson Daku, A. Hauser and N. Avarvari
    RSC Advances, 3 (2013), p3218-3221
    DOI:10.1039/c3ra21702g | unige:27369 | Abstract | Article HTML | Article PDF
The structurally characterized tetrathiafulvalene-1,2,4,5-tetrazine donor–acceptor system shows redox tuneable intramolecular charge transfer, solvatochromic and electrochromic behaviour. Attachment of a dipicolyl-amine chelating unit affords a multifunctional ligand, which allows the preparation of the ZnCl2 complex in which an anion-π interaction is seen.
  • Tetrathiafulvalene-Benzothiadiazoles as Redox-Tunable Donor-Acceptor Systems: Synthesis and Photophysical Study
    F. Pop, A. Amacher, N. Avarvari, J. Ding, L.M. Lawson Daku, A. Hauser, M. Koch, J. Hauser, S.-X. Liu and S. Decurtins
    Chemistry - A European Journal, 19 (7) (2013), p2504-2514
    DOI:10.1002/chem.201202742 | unige:26401 | Abstract | Article PDF
Electrochemical and photophysical analysis of new donor–acceptor systems 2 and 3, in which a benzothiadiazole (BTD) unit is covalently linked to a tetrathiafulvalene (TTF) core, have verified that the lowest excited state can be ascribed to an intramolecular-charge-transfer (ICT) π(TTF)→π*(benzothiadiazole) transition. Owing to better overlap of the HOMO and LUMO in the fused scaffold of compound 3, the intensity of the 1ICT band is substantially higher compared to that in compound 2. The corresponding CT fluorescence is also observed in both cases. The radical cation TTF+. is easily observed through chemical and electrochemical oxidation by performing steady-state absorption experiments. Interestingly, compound 2 is photo-oxidized under aerobic conditions.



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Last update Friday December 08 2017