Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics

The aim of this review is to give an update on current progress in the synthesis, properties and applications of thiophene-based conjugated systems bearing tetrathiafulvalene (TTF) units. We focus mostly on the synthesis of poly- and oligothiophenes with TTF moieties fused to the thiophene units of the conjugated backbone either directly or via a dithiin ring. The electrochemical behaviour of these materials and structure-property relationships are discussed. The study is directed towards the development of a new type of organic semiconductors based on these hybrid materials for application in organic field effect transistors and solar cells.

Negishi coupling in the synthesis of advanced electronic, optical, electrochemical, and magnetic materials

Negishi coupling is an efficient and versatile tool for selective C–C bond formation in the synthesis of organic electronic, optical, electrochemical, and magnetic materials.

THEORETICAL INVESTIGATIONS OF THE CHARGE TRANSFER PROPERTIES IN OLIGOTHIOPHENE DERIVATIVES

The structures of 5,5′-bis(naphth-2-yl)- 2,2′-bithiophene (NaT2), 5,5″-bis(naphth-2-yl)-2,2′:5′,2′-terthiophene (NaT3), 5,5‴-bis(naphth-2-yl)-2,2′:5′,2″:5″,2‴-tetrathiophene (NaT4), 5,5″″-bis(naphth-2-yl)-2,2′:5′,2″:5″,2‴:5‴,2″″-quinquethiophene (NaT5) and 5,5′″″-bis(naphth-2-yl)-2,2′:5′,2″:5″,2‴:5‴,2″″:5″″,2′″″-sexithiophene (NaT6) have been optimized at PBE1PBE/6-31G* level of theory. By increasing the chain length (thiophene units) energy gap decreases. The hole reorganization energy also decreases from NaT2–NaT6 . We have observed that mobility of NaT5 and NaT6 can be enhanced by minimizing the polarization and relaxation. The end-capped naphthyl groups have been rotated from 0°–60° in the case study of NaT2 , it was found that hole reorganization energy increases with the increment in angle. Furthermore the charge transport properties of 5,5′-bis(thionaphth-2-yl)-2,2′-bithiophene (TNT2), 5,5″-bis(thionaphth-2-yl)-2,2′:5′,2″-terthiophene (TNT3), and 5,5‴-bis(thionaphth-2-yl)-2,2′:5′,2″:5″,2‴-quaterthiophene (TNT4) have been investigated at the same level of theory. It has been studied that cis isomers have higher hole reorganization energies as compared to trans ones thus these isomers would diminish the mobility.

Sexithiophenes as efficient luminescence quenchers of quantum dots

Sexithiophenes 1a and 1b, in which a 4-(dimethylamino)phenyl unit is incorporated as an end-capping group, were synthesised and characterised by cyclic voltammetry, absorption spectroscopy and UV-vis spectroelectrochemistry. Additionally, their ability to function as effective luminescence quenchers for quantum dot emission was studied by photoluminescence spectroscopy and compared with the performance of alkyl end-capped sexithiophenes 2a and 2b.

Incorporation of fused tetrathiafulvalenes (TTFs) into polythiophene architectures: varying the electroactive dominance of the TTF species in hybrid systems

A novel polythienylenevinylene (PTV) and two new polythiophenes (PTs), featuring fused tetrathiafulvalene (TTF) units, have been prepared and characterized by ultraviolet-visible (UV-vis) and electron paramagnetic resonance (EPR) spectroelectrochemistry. All polymers undergo two sequential, reversible oxidation processes in solution. Structures in which the TTF species is directly linked to the polymer backbone (2 and 4) display redox behavior which is dictated by the fulvalene system. Once the TTF is spatially removed from the polymer chain by a nonconjugated link (polymer 3), the electroactivity of both TTF and polythiophene moieties can be detected. Computational studies confirm the delocalization of charge over both electroactive centers (TTF and PT) and the existence of a triplet dication intermediate. PTV 4 has a low band gap (1.44 eV), is soluble in common organic solvents, and is stable under ambient conditions. Organic solar cells of polymer 4:[6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) have been fabricated. Under illumination, a photovoltaic effect is observed with a power conversion efficiency of 0.13% under AM1.5 solar simulated light. The onset of photocurrent at 850 nm is consistent with the onset of the pi-pi absorption band of the polymer. Remarkably, UV-vis spectroelectrochemistry of polymer 4 reveals that the conjugated polymer chain remains unchanged during the oxidation of the polymer.

Synthesis of an End-Capped Sexithiophene Bearing Fused Tetrathiafulvalene (TTF) Units

[structure: see text] We report the synthesis of a novel end-capped sexithiophene derivative bearing two pendent, fused tetrathiafulvalene (TTF) units linked to the main chain through 1,4-dithiin heterocycles. Cyclic voltammetry and absorption spectroscopy are used to investigate the electronic properties of this hybrid electroactive material. The oligomer has a band gap of 2.1 eV, and the material can be oxidized through the sexithiophene and TTF units simultaneously.

Triphenylamine-thienylenevinylene hybrid systems with internal charge transfer as donor materials for heterojunction solar cells

Star-shaped molecules based on a triphenylamine core derivatized with various combinations of thienylenevinylene conjugated branches and electron-withdrawing indanedione or dicyanovinyl groups have been synthesized. UV-vis absorption and fluorescence emission data show that the introduction of the electron-acceptor groups induces an intramolecular charge transfer that results in a shift of the absorption onset toward longer wavelengths and a quenching of photoluminescence. Cyclic voltammetry shows that all compounds present a reversible first oxidation process whose potential increases with the number of electron-withdrawing groups in the structure. Prototype bulk and bilayer heterojunction solar cells have been realized using fullerene C60 derivatives as acceptor material. The results obtained with both kinds of devices show that the introduction of electron-acceptor groups in the donor structure induces an extension of the photoresponse in the visible spectral region, an increase of the maximum external quantum efficiency, and an increase of the open-circuit voltage under white light illumination. These synergistic effects allow reaching power conversion efficiencies of approximately 1.20% under simulated AM 1.5 solar irradiation at 100 mW cm(-2).

X-Shaped Oligothiophenes as a New Class of Electron Donors for Bulk-Heterojunction Solar Cells

Four X-shaped oligothiophenes with different conjugation length were investigated as novel electron donors in single-layer bulk-heterojunction solar cells. The UV-vis absorption spectra of blends of compounds 1-4 with 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C(61) show a remarkably red shift and broadening with increasing thiophene number at each of the four branches. The performance of the photovoltaic cells varied significantly with molecular structures of the four oligothiophenes. Conversion efficiencies increased from 0.008% to 0.8% with changing the electron donors from 1 to 4. The maximum incident photon-to-current conversion efficiency of the device based on 4 reaches 31.6%, much higher than those of three other compounds 1-3. Remarkable improvement of the device performance was achieved with increasing the substituted thiophene number. The results show that the photovoltaic effect is dependent on the structural characteristics and the film forming abilities of the X-shaped thiophenes.