Helicene Appended Benzothiadiazoles as Chiral Emitters

A homologous series of 4,7-bis(aryl) substituted benzothiadiazole (BTD) compounds, containing the helicenic derivatives bis([4]helicene), bis([5]helicene) and bis([6]helicene), have been prepared upon a double Suzuki coupling between 3,6-bis(pinacolyl-borane)-BTD and the corresponding bromo-aryl precursors. The single crystal X-ray structure of the bis([4]helicene) compound shows the existence of both helicities (M) and (P) on the same molecule. All the compounds of the series are highly emissive in solution, with quantum yields of the emission ranging from 50 to 91 %. The enantiopure compounds (M,M) and (P,P) for the BTD-bis([6]helicene) have been prepared from the corresponding enantiopure 2-bromo-[6]helicene precursors. Their chiroptical properties have been investigated in correlation with density functional theory (DFT) calculations, which allowed to confidently assign the absolute configuration of the helicene arms and to characterize the different electronic transitions, including the low energy charge transfer excitation from helicenes to BTD. The enantiomerically pure fluorophores (M,M)- and (P,P)-BTD-bis([6]helicene), which exist in solution as two main conformers, according to the DFT calculations, show CPL activity in solution, with glum factors of ≈1.7×10-3 at λem=525 nm, and also in the solid state, with glum factors of ≈1.2×10-3 in spite of the strong decrease of the quantum efficiency.

Field-induced mononuclear cobalt(II) single-molecule magnet (SMM) based on a benzothiadiazole-ortho-vanillin ligand

A unique π-conjugated benzothiadiazole-ortho-vanillin ligand (HL), characterized by single crystal X-ray diffraction and DFT calculations, has been prepared by condensation between 4-amino-benzothiadiazole (BTD) and ortho-vanillin. Its reaction with cobalt(II) acetate...

Dimensionality Control in Crystalline Zinc(II) and Silver(I) Complexes with Ditopic Benzothiadiazole-Dipyridine Ligands

Three 2,1,3-benzothiadiazole-based ligands decorated with two pyridyl groups, 4,7-di(2-pyridyl)-2,1,3-benzothiadiazol (2-PyBTD), 4,7-di(3-pyridyl)-2,1,3-benzothiadiazol (3-PyBTD) and 4,7-di(4-pyridyl)-2,1,3 benzothiadiazol (4-PyBTD), generate ZnII and AgI complexes with a rich structural variety: [Zn(hfac)2(2-PyBTD)] 1, [Zn2(hfac)4(2-PyBTD)] 2, [Ag(CF3SO3)(2-PyBTD)]23, [Ag(2-PyBTD)]2(SbF6)24, [Ag2(NO3)2(2-PyBTD)(CH3CN)] 5, [Zn(hfac)2(3-PyBTD)] 6, [Zn(hfac)2(4-PyBTD)] 7, [ZnCl2(4-PyBTD)2] 8 and [ZnCl2(4-PyBTD)] 9 (hfac = hexafluoroacetylacetonato). The nature of the resulting complexes (discrete species or coordination polymers) is influenced by the relative position of the pyridyl nitrogen atoms, the nature of the starting metal precursors, as well as by the synthetic conditions. Compounds 1 and 8 are mononuclear and 2, 3 and 4 are binuclear species. Compounds 6, 7 and 9 are 1D coordination polymers, while compound 5 is a 2D coordination polymer, the metal ions being bridged by 2-PyBTD and nitrato ligands. The solid-state architectures are sustained by intermolecular π–π stacking interactions established between the pyridyl group and the benzene ring from the benzothiadiazol moiety. Compounds 1, 2, 7–9 show luminescence in the visible range. Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) calculations have been performed on the ZnII complexes 1 and 2 in order to disclose the nature of the electronic transitions and to have an insight on the modulation of the photophysical properties upon complexation.

Covalent non-fused tetrathiafulvalene–acceptor systems

The main families of non-fused TTF–acceptors are discussed with a special focus on their characteristics and properties.

A hybrid electron donor comprising cyclopentadithiophene and dithiafulvenyl for dye-sensitized solar cells

Two new photosensitizers featured with a cyanoacrylic acid electron acceptor (A) and a hybrid electron donor (D) of cyclopentadithiophene and dithiafulvenyl, either directly linked or separated by a phenyl ring, were synthesized and characterized. Both of them undergo two reversible oxidations and strongly absorb in the visible spectral region due to a photo-induced intramolecular charge-transfer (ICT) transition. To a great extent, the electronic interaction between the D and A units is affected by the presence of a phenyl spacer. Without a phenyl ring, the D unit appears more difficult to oxidize due to a strong electron-withdrawing effect of the A moiety. In sharp contrast, the insertion of the phenyl ring between the D and A units leads to a broken π-conjugation and therefore, the oxidation potentials remain almost unchanged compared to those of an analogue without the A group, suggesting that the electronic coupling between D and A units is relatively weak. As a consequence, the lowest-energy absorption band shows a slight hypsochromic shift upon the addition of the phenyl spacer, indicative of an increased HOMO-LUMO gap. In turn, the direct linkage of D and A units leads to an effective π-conjugation, thus substantially lowering the HOMO-LUMO gap. Moreover, the application in dye-sensitized solar cells was investigated, showing that the power conversion efficiency increases by the insertion of the phenyl unit.

Voltammetric studies on the inter-relationship between the redox chemistry of TTF, TTF+˙, TTF2+ and HTTF+ in acidic media

The chemistry of oxidized forms of TTF in acidified CH₃CN has been established using electrochemical and spectroscopic techniques.

Dithiafulvenyl–triphenylamine organic dyes with alkyl chains for efficient coadsorbent-free dye-sensitized solar cells

Dithiafulvenyl–triphenylamine (DTF–TPA) based D-D-η-A organic dyes with different alkyl chains attached on the DTF unit were synthesized to investigate the effect of alkyl chain lengths on the photovoltaic performances of dye-sensitized solar cells.

Anthanthrene dye-sensitized solar cells: influence of the number of anchoring groups and substitution motif

Four anthanthrene-based molecules were synthesized as sensitizers in dye-sensitized solar cells, leading to the best overall efficiency up to 5.3%.

Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives

Stille and Sonogashira coupling strategies allowed the preparation of luminescent TTF-benzothiadiazole donor–acceptor compounds with direct linkage or an acetylenic spacer.