Fused Thiophene Rings Research Articles

Synthesis and Structure of Bull’s Horn-Shaped Oligothienoacene with Seven Fused Thiophene Rings

A novel bull's horn-shaped oligothienoacene with seven fused thiophene rings (1) based on dithieno[2,3-b:2',3'-d]thiophene (2) was efficiently synthesized. X-ray diffraction data indicate that 1 possesses an extraordinary compressed sandwich-herringbone arrangement and shows strong intermolecular S···C and S···S interactions. In addition, the UV/vis properties, theoretical calculations, and cyclic voltammetry behaviors of 1 are also described.

Thienoacene‐Based Organic Semiconductors

Thienoacenes consist of fused thiophene rings in a ladder-type molecular structure and have been intensively studied as potential organic semiconductors for organic field-effect transistors (OFETs) in the last decade. They are reviewed here. Despite their simple and similar molecular structures, the hitherto reported properties of thienoacene-based OFETs are rather diverse. This Review focuses on four classes of thienoacenes, which are classified in terms of their chemical structures, and elucidates the molecular electronic structure of each class. The packing structures of thienoacenes and the thus-estimated solid-state electronic structures are correlated to their carrier transport properties in OFET devices. With this perspective of the molecular structures of thienoacenes and their carrier transport properties in OFET devices, the structure-property relationships in thienoacene-based organic semiconductors are discussed. The discussion provides insight into new molecular design strategies for the development of superior organic semiconductors.

Optoelectronic and Charge Transport Properties of Oligomers Based on Phenylethynylene Units Linked to Thieno-acenes: A DFT Study

The geometries and electronic properties of a series of π-conjugated oligomers, as possible precursors of n-type materials, have been studied with the help of density functional theory. The selected compounds are based on phenylethynylene moieties alternated with thieno-acene units containing up to four fused thiophene rings, PhEtTx=1−4. The optoelectronic properties and conducting capability were investigated through the HOMO→LUMO excitation energies, LUMO energy levels, electron affinities, intramolecular reorganization energies, and electronic coupling. All studied properties agree that oligomers based on PhEtTx=1−4 show adequate values concerning electron affinities, LUMO levels, and intramolecular reorganization energy to be considered n-type semiconductor candidates. Besides, the optical bandgaps are close to 2 eV, which is the threshold for a material to be considered as potentially suitable in the field of solar cells.

Theoretical Study of Bis(phenylethynyl)thienoacenes as Precursors of Molecular Wires for Molecular Electronics

The geometries and electronic properties of a series of bis(phenylethynyl)thienoacenes as precursors of n-type materials with desirable (opto)electronic properties have been studied from a theoretical perspective: 2,5-bis-phenylethynyl-thiophene (PhEtT), 2,5-bis-phenylethynyl-thieno[3,2-b]thiophene (PhEtT2), 2,6-bis-phenylethynyl-dithieno[3,2-b;2′,3′-d]thiophene (PhEtT3), and 2,6-bis-phenylethynyl-3,4,7,8-tetrathia-dicyclopenta[a,e]pentalene (PhEtT4). This has allowed performance of a comparative study of the influence of the number of fused thiophene rings on the studied properties. The (opto)electronic properties and conducting capability were investigated through the HOMO → LUMO excitation energy, bond length alternation (BLA), LUMO energy, electron affinity, and intramolecular reorganization energy. Also, the influence of planarity on electrical conductivity has been analyzed by means of the natural bond orbital (NBO) approach together with the theory of atoms in molecules (AIM). From this study it follows that the increase in the number of fused thiophene rings does not significantly affect those properties related to aromaticity such as BLA, rotational barriers, or charge transference between the different aromatic rings, while that increase leads to an easier charge injection and brings on an enhancement of the n-type character.

FT Raman and DFT Study on a Series of All‐anti Oligothienoacenes End‐Capped with Triisopropylsilyl Groups

Herein, we study the pi-conjugational properties of a homologous series of all-anti oligothienoacenes containing four to eight fused thiophene rings by means of FT Raman spectroscopy and DFT calculations. The theoretical analysis of the spectroscopic data provides evidence that selective enhancement of a very limited number of Raman scatterings is related to the occurrence in these oligothienoacenes of strong vibronic coupling between collective nu(C=C) stretching modes in the 1600-1300 cm(-1) region and the HOMO/LUMO frontier orbitals (HOMO=highest occupied molecular orbital; LUMO=lowest unoccupied molecular orbital). The correlation of the Raman spectroscopic data and theoretical results for these all-anti oligothienoacenes with those previously collected for a number of all-syn oligothienohelicenes gives further support to the expectation that cross-conjugation is dominant in heterohelicenes. Fully planar all-anti oligothienoacenes display linear pi conjugation which seemingly does not reach saturation with increasing number of annulated thiophene rings in the oligomeric chain at least up to the octamer.

Alkylsubstituted Thienothiophene Semiconducting Materials: Structure−Property Relationships

A family of conjugated polymers with fused structures consisting of three to five thiophene rings and with the same alkyl side chains has been synthesized as a means to understand structure-property relationships. All three polymers showed well-extended conjugation through the polymer backbone. Ionization potentials (IP) ranged from 5.15 to 5.21 eV; these large values are indicative of their excellent oxidative stability. X-ray diffraction and AFM studies suggest that the polymer with the even number of fused thiophene rings forms a tight crystalline structure due to its tilted side chain arrangement. On the other hand, the polymers with the odd number of fused thiophene rings packed more loosely. Characterization in a field-effect transistor configuration showed that the mobility of the polymer with the even number of rings is 1 order of magnitude higher than its odd-numbered counterparts. Through this structure-property study, we demonstrate that proper design of the molecules and properly arranged side chain positions on the polymer backbone can greatly enhance polymer electronic properties.

チオフェン縮環トリフェニレン誘導体の合成、構造、および物性評価

チオフェン縮環トリフェニレン誘導体の合成、構造、および物性評価

Effect of ring fusion on the amplified spontaneous emission properties of oligothiophenes

We report the observation of amplified spontaneous emission (ASE) in oligothienoacenes, oligothiophenes composed solely of fused thiophene rings, doped into polystyrene films. The effect of ring fusion on the ASE properties has been investigated by comparing the performance of a pentathienoacene derivative, 2,6-bis-triisopropylsilanyl-α-pentathienoacene (BT-PTA), with that of its corresponding non-fused oligothiophene, 5,5″-bis-triisopropylsilanyl-α-terthiophene (BT-α3T), whose synthesis is also reported here. The spectral properties of both systems have been studied by UV-vis optical absorption and photoluminescence in solution at both room and low temperature and interpreted by means of density functional theory (DFT) and time dependent DFT quantum chemical calculations. The dependence of ASE in terms of threshold, linewidth and emission wavelength on the concentration of active material in the films has been investigated in detail, allowing for optimization of the ASE performance. The best results were obtained for oligomer concentrations between 10 and 30 wt%. BT-PTA-doped films show ASE thresholds as low as 10 kW·cm−2, one order of magnitude lower than those of films doped with BT-α3T. These results indicate that the materials are good candidates as active laser materials and that their performance can be improved by adjusting the concentration of material in the film.

Tetrathienoacene Copolymers As High Mobility, Soluble Organic Semiconductors

Increasing the rigidity of the thiophene monomer through the use of an alkyl-substituted core that consists of four fused thiophene rings is shown to be a promising route toward high-performance organic semiconductors. We report on a dialkylated tetrathienoacene copolymer that can be deposited from solution to yield ordered films with a short pi-pi distance of 3.76 A and with a field-effect hole mobility that exceeds 0.3 cm2/V.s. This polymer enables simple transistor fabrication at relatively low temperatures, which is particularly important for the realization of large-area, mechanically flexible electronics.

Fourier Transform Raman and DFT Study of Three Annulated Oligothiophenes with Different Molecular Shapes

Herein, we study the conjugation properties of three different thienoacenes, each of which has three or four fused thiophene rings, by means of Fourier transform Raman spectroscopy. The B3LYP/6-31G** vibrational analysis of all of the collected spectroscopic data evidences that the selective enhancement of a limited number of Raman scatterings is related to the occurrence in the three thienoacenes of a vibronic coupling between the lowest unoccupied frontier molecular orbital (LUMO) and some Raman-active skeletal nu(C==C) stretching modes of 1600-1300 cm(-1).

Combined Quantum Chemical Density Functional Theory and Spectroscopic Raman and UV−vis−NIR Study of Oligothienoacenes with Five and Seven Rings

In this article, we report the characterization of novel oligothienoacenes with five and seven fused thiophene rings, materials with potential applications in organic electronics. In contrast to usual alpha-linked oligothiophenes, these fused oligothiophenes have a larger band gap than most semiconductors currently used in the fabrication of organic field-effect transistors (OFETs) and therefore they are expected to be more stable in air. The synthesis of these fused-ring oligomers was motivated by the notion that a more rigid and planar structure should reduce defects (such as torsion about single bonds between alpha-linked units or S-syn defects) and thus improve conjugation for better charge-carrier mobility. The conjugational properties of these two molecular materials have been investigated by means of FT-Raman spectroscopy, revealing that conjugation still increases in passing from the five-ring oligomer to that with seven-rings. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G level, to assess information regarding the minimum-energy molecular structure, topologies, and absolute energies of the frontier molecular orbitals (MOs.) around the gap, vibrational normal modes related to the main Raman features, and vertical one-electron excitations giving rise to the main optical absorptions.