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A hybrid tetrathiafulvalene–oligothiophene compound has been synthesised, in which the fulvalene unit is fused on both sides to an end-capped septithiophene oligomer. The compound (1) has been studied by cyclic voltammetry, UV-vis spectroelectrochemistry and X-ray crystallography. The properties of this material are compared to the half-unit (9), w...
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... order to investigate the electrochemical properties and consequences of fusing TTF directly between the 7T chains, cyclic voltammetry experiments were performed on compounds 1 and 9 ( Fig. 1 and Table 1). The oxidation of 9 shows three sequential oxidation waves. ...
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... the presence of the TTF core in 1 may lead us to expect two discernible reversible waves in the corresponding cyclic voltammogram, the oxidation of 1 in fact shows a complex series of redox processes over a wide potential range. The data are given in Table 1, but it is difficult to explain and interpret the results with a high level of confidence. It is reasonable to assume that the additional peak for 1, seen at the half-wave potential of Scheme 1 Synthesis of the TTF-bis(septithiophene) 1 and its 1,3- dithiole-2-one precursor 9. +0.25 V, suggests the oxidation of the TTF unit. ...
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... electrochemical HOMO-LUMO gaps of the materials were obtained from the difference in the onsets of the first oxidation and reduction peaks (Table 1). Using data referenced to the ferrocene/ferrocenium redox couple, HOMO and LUMO energies were calculated by subtracting the onsets from the HOMO of ferrocene, which has a known value of À4.8 eV. ...
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... the terminal bithiophene units with the syn conformation were twisted to an anti orien- tation and this structure was allowed to relax to a local minimum. The calculated HOMO-LUMO gap for the all-anti conformer (2.49 eV) was found to be closer to the experimental HOMO-LUMO gap (Table 1), than the structure obtained from crystallography (2.70 eV). Also, the all-anti conformer was lower in energy, showing that this is the preferred geometry in the gas phase. ...
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Citations
... For this reason, hole-mobility was measured by the space-charge-limite rent (SCLC) method. SCLC is one of the most widely used techniques [44,45] to m charge mobility in the direction perpendicular to the film, which is the directio relevant for photovoltaic applications or light emitting diodes [46,47]. Hole-only d having the following structure: ITO/PEDOT:PSS/Hx/MoO3/Au, were realized and acterized under the same experimental conditions, such as in the dark, in a vacuu mbar) and at a controlled temperature. ...
... For this reason, hole-mobility was measured by the space-charge-limited current (SCLC) method. SCLC is one of the most widely used techniques [44,45] to measure charge mobility in the direction perpendicular to the film, which is the direction most relevant for photovoltaic applications or light emitting diodes [46,47]. Hole-only devices having the following structure: ITO/PEDOT:PSS/Hx/MoO 3 /Au, were realized and characterized under the same experimental conditions, such as in the dark, in a vacuum (10 −3 mbar) and at a controlled temperature. ...
We have synthetized two classes of dibenzofulvene-arylamino derivatives with an H-shape design, for a total of six different molecules. The molecular structures consist of two D-A-D units connected by a thiophene or bitiophene bridge, using diarylamino substituents as donor groups anchored to the 2,7- (Group A) and 3,6- (Group B) positions of the dibenzofulvene backbone. The donor units and the thiophene or bithiophene bridges were used as chemico-structural tools to modulate electro-optical and morphological-electrical properties. A combination of experiments, such as absorption measurements (UV-Vis spectroscopy), cyclic voltammetry, ellipsometry, Raman, atomic force microscopy, TD-DFT calculation and hole-mobility measurements, were carried out on the synthesized small organic molecules to investigate the differences between the two classes and therefore understand the relevance of the molecular design of the various properties. We found that the anchoring position on dibenzofulvene plays a crucial key for fine-tuning the optical, structural, and morphological properties of molecules. In particular, molecules with substituents in 2,7 positions (Group A) showed a lower structural disorder, a larger molecular planarity, and a lower roughness.
... In the present case, we applied the space charge-limited current (SCLC) technique 40,43 to measure charge mobility in the direction perpendicular to the film, which is the direction most relevant for photovoltaic applications or light-emitting diodes. 44,45 The effect of the different molecular structures on charge transport has been studied by spin-casting solutions of TN3, T2N3, mTN3, and mT2N3 from chlorobenzene onto prepatterned ITO substrates, to fabricate hole-only devices having the following architecture: ITO/PEDOT:PSS/HTM/MoO3/Au. The room-temperature current−voltage (J−V) characteristics of each material investigated are shown in Figure 8 in semi-log scale (open circles). We can clearly see that under the same bias condition, the current density is higher for materials belonging to group I (TN3, T2N3) than group II (mTN3, mT2N3). ...
... [18] Recently, we reported the synthesis of a monodisperse hybrid compound bearing two septithiophene fragments bridged with a fused tetrathiafulvalene (TTF) unit (2; Scheme 1), which exhibits complex redox behavior and can be oxidized up to the octacation. [19] The end-capped oligothiophene 3 having a fused dithiolone unit is similar to that of 4, which was used for the synthesis of compound 2. Both compounds can be used as synthetic equivalents of dinucleophilic synthons for constructing a series of spiro structures with the sulfur handles providing space separation of the two conjugated backbones and the possibility for spiro conjugation. ...
... Communications the Ge cruciform exhibited distinct signs of aggregation similar to those observed earlier for hybrid TTF/oligothiophene compounds. [19,24] To disrupt aggregation in solution (e.g., for solution state NMR experiments and solution processing), it was necessary to add a small amount of CS 2 . Crystals of compound 6 suitable for X-ray analysis were grown by slow liquid diffusion of ethanol into a CH 2 Cl 2 /CS 2 (3:1) solution. ...
... It is interesting to compare these results with other mobility measurements in the direction perpendicular to the film on related materials. Highly dispersive charge transport has already been observed in the case of 2 and septithiophene 4, [19] thus leading to a mobility value of 1.2 10 À6 cm 2 V À1 s À1 for 4 and 2.5 10 À6 cm 2 V À1 s À1 for 2. [19] The mobility of 6 is an order of magnitude higher than that reported for sexithiophene, [33] and the same order of magnitude as that reported for poly (3-hexylthiophene). [34] To demonstrate that the stacking structure is suitable for organic electronic devices, we made BHJ solar cells containing the Ge cruciform 6 as the donor and PC 71 BM as the acceptor. ...
X marks the spot! A fascinating packing motif is observed in a novel cruciform oligothiophene containing a Ge (violet; see picture) spiro center. Long-range interchain interactions between molecules and strong electronic coherence between orthogonal chains within the molecules are present. Such ordering is advantageous for bulk charge transport as demonstrated by high short-circuit currents in bulk heterojunction organic solar cells.
The development of biosensors capable of achieving accurate and precise molecular measurements in the living body in pH-variable biological environments (e.g. subcellular organelles, biological fluids and organs) plays a significant role in personalized medicine. Because they recapitulate the conformation-linked signaling mechanisms, electrochemical aptamer-based (E-AB) sensors are good candidates to fill this role. However, this class of sensors suffers from a lack of a stable and pH-independent redox reporter to support their utility under pH-variable conditions. Here, in response, we demonstrate the efficiency of an electron donor π-extended tetrathiafulvalene (exTTF) as an excellent candidate (due to its good electrochemical stability and no proton participation in its redox reaction) of pH-independent redox reporters. Its use has allowed improvement of E-AB sensing performance in biological fluids under different pH conditions, achieving high-frequency, real-time molecular measurements in biological samples both in vitro and in the bladders of living rats.
Hole transporting materials (HTMs) play a crucial role in developing highly efficient and stable perovskite solar cells (PSCs). Their function is to extract and transport hole carriers, but at the same time protect the perovskite layer from environmental conditions (n-i-p PSCs). Therefore, there is a need to develop new HTMs to better balance all of the above functions and performances to make efficient, stable and possibly low-cost PSCs. To address these issues, we studied the structure-performance relationship of a series of recently synthesized star-shaped molecules characterized by a dibenzofulvene core, a thiophene ring and three arylamino moieties, but varying in size (thiophene number) and shape (anchoring position of arylamines to the core). By the interplay between size and shape, we managed to tune the hole mobility by up to three orders of magnitude, and our best compound (T2N3) showed a zero-field mobility value (3 Â 10 À5 cm 2 V À1 s À1) comparable to that of spiro-OMeTAD. Not only the mobility but also the main charge transport parameters were analyzed from the temperature-dependent space charge limited current characteristics. Usually, this analysis relies on simplified empirical equations but in the present case they were extracted by solving drift-diffusion equations. More importantly, we parametrized the field and temperature mobility dependence by simulating hopping transport via sites located on either regular grids or randomly distributed ones. The resulting transport parameters were correlated with the structure and morphology of the materials. The relatively good mobility of T2N3 combined with its good film-forming properties, which translates into good interaction with perovskites (efficient hole extraction), led to PSC efficiencies comparable to those of spiro-OMeTAD. Moreover, the laboratory synthesis of T2N3 was simpler and cheaper than that of commercially available spiro-OMeTAD. Importantly, non-encapsulated solar cells employing T2N3 showed an 80% efficiency lifetime of 2400 h (100 days), which is triple that of spiro-OMeTAD based ones. Thus, we propose T2N3 as a promising alternative to the expensive and poorly stable spiro-OMeTAD.
4-(9’-Hexylcarbazol-3’-yl)benzaldehyde (Cz-Ph-CHO: 4) and 4-(9’-hexylcarbazol-3’-yl)benzylidenemalononitrile (Cz-Ph-CN: 5) were synthesised with the structure of D-π-A, where carbazole, phenylene and formyl/dicyanovinyl groups act as electron donor (D), pi-spacer (π) and electron acceptor (A) units, respectively. The thermal, electrochemical, optical and intramolecular charge transfer (ICT) properties of compounds 4 and 5 were investigated. Compounds 4 and 5, in particular their ICT behaviour, were also compared with the closely related structure, 2-(9’-hexylcarbazol-3’-yl)-5-pyridinecarbaldehyde (Cz-Py-CHO: 7). For the purpose of tuning chemical structure to obtain targeted properties, electrochemical data and absorption and emission measurements suggest that the dicyanovinyl unit in compound 5 is a better acceptor than formyl in compound 4, and that pyridine in compound 7 is a better π-spacer than benzene in compound 4, in exerting ICT characteristics such as fluorosolvatochromism and Stokes shifts.
A series of TTF and EDT-TTF derived donors bearing thiophene, bithiophene and terthiophene side chains is described, from which a group of six radical cation salts with polyiodide ions were formed and structurally characterised. Typically, they contain complex networks of pentaiodide or triiodide anions or both, in some cases including further iodine, with networks of eight, ten, twelve or sixteen iodine atoms. Donor monocations form face-to-face pairs, but tetrakis-substituted donors are slipped along their main axis so the donor side chains can wrap around each other.
Through density functional theory, we studied molecular device composed of a single tetrathiafulvalene (TTF) molecule connected with the zigzag graphene nanoribbon electrodes by four different junctions. Interestingly, some devices exhibit half-metallic behavior and can bring out perfect spin filtering effect and remarkable negative differential resistance behavior. The current-voltage characteristics shows that these four devices possess different spin current values. We find that the TTF molecules have all been stretched during interaction with the electrodes in four devices. This leads to three devices’ Fermi levels down-shifted into the valence-band, so these devices exhibit half-metallic properties. The underlying mechanisms of different spin current values are attributed to the different electron transmitting ways (by chemical bond or through hopping between atoms). These results suggest that the device properties and conductance are controlled by different junctions. Our work predicts an effective way for designing high performance spin-injected molecular devices.
A new dual-chain oligothiophene-based organic semiconductor, EH-5T-TTC, is presented. The molecule contains two conjugated chains linked by a fused tetrathiocin core. X-ray crystallography reveals a boat conformation within the 8-membered sulfur heterocycle core and extensive - and intermolecular sulfur-sulfur interactions in the bulk, leading to a 2-dimensional structure. This unusual molecule has been studied as an additive in ternary organic solar cells in blends containing the electron donor PTB7-Th and both fullerene (PC71BM) and non-fullerene acceptors ITIC and EH-IDTBR. By incorporating EH-5T-TTC as a ternary component, the power conversion efficiency of the binary blends containing non-fullerene acceptor increases by 17 % (from 7.8 % to 9.2 %) and by 85 % for the binary blend with fullerene acceptor (from 3.3 % to 6.3%). Detailed characterisation of the ternary blend systems implies that the ternary small molecule EH-5T-TTC functions differently in polymer:fullerene and polymer:non-fullerene blends and has dual functions of morphology modification and complementary spectral absorption.
A series of novel star-shaped oligofluorene–thiophene–tetrathiafulvalene systems have been synthe- sised, following different synthetic routes. Each system incorporates a tetrathiafulvalene redox-active centre and four oligofluorene arms, providing a two-dimensional character of the conjugated backbone. The oligomers differ in the number of fluorene units present in the arms (1 to 4) and the terminal groups at the end of each arm (H or trimethylsilyl). Half-unit oligofluorene systems possessing a 1,3-dithiole-2- one core (a known precursor to the tetrathiafulvalene centre) have been synthesised in order to compare the thermal, optical and electrochemical properties. These half-unit systems consist of a 1,3- dithiole-2-one core fused to a thiophene unit at the 3- and 4-positions. Two oligofluorene arms consisting of 1 to 4 monomer units per arm are positioned at the 4- and 6-positions of the thiophene unit, affording extended conjugation through the thiophene centre. The half-unit systems are found to be moderate emitters in the solution-state, however, the star-shaped systems bearing the tetrathiafulvalene core exhibit inhibited fluorescence in both the solution and solid states. We have demonstrated that the emission of the tetrathiafulvalene systems can be enhanced through the oxidation of the redox-centre followed by a consecutive reaction of the strongly electrophilic tetrathiafulvalene dication with such nucleophiles as water and hydrazine. The result of these reactions leads to an increase in the photoluminescence of these systems, affording the opportunity for the tetrathiafulvalene materials to be used as photonic materials in moisture indicators.
