Novel Thiophene–Phenylene–Thiophene Fused Bislactam-Based Donor–Acceptor Type Conjugate Polymers: Synthesis by Direct Arylation and Properties

Three new donor–acceptor copolymers based on thiophene–phenylene–thiophene fused bislactam and various donors (3,4-dodecylthiophene, 4,4′-didodecyl-2,2′-bithiophene, and ethylenedioxythiophene) were synthesized, characterized, and used in field-effect transistors. Polycondensation was performed using nonactivated thiophene derivatives by employing palladium-catalyzed direct arylation under phosphine-free conditions. This method is superior to traditional cross-coupling polymerization because it requires fewer synthetic operations and does not employ toxic organometallic intermediates. Regioselective polymers can also be generated by using β-substituted thiophene derivatives. The studied polymers were tested in a bottom gate top contact thin film transistor (OTFT) architecture. The best electronic performance was shown by polymer <b>P3</b>, with enhanced π-conjugation due to the appearance of intramolecular attractive interactions

Phenyl- and Thienyl-Ended Symmetric Azomethines and Azines as Model Compounds for n‑Channel Organic Field-Effect Transistors: An Electrochemical and Computational Study

The formation energy and stability of radical anions in a series of 12 phenyl- and 2-thienyl-ended linear, symmetric azomethines and azines were investigated by cyclic voltammetry. Replacing 1,4-phenylene with 2,5-thienylene cores and substitution with cyano or methyl moieties have allowed the lowering of lowest unoccupied molecular orbital energy levels even by 1 eV. Methyl capping stabilizes electron carriers (radical anions) toward dimerization, and the mechanism of such radical anion dimerization has been clarified by cyclic voltammetric kinetic analysis. The results have been compared with optical parameters and supported by density functional theory calculations

Dialkoxybithiazole: A New Building Block for Head-to-Head Polymer Semiconductors

Polymer semiconductors have received great attention for organic electronics due to the low fabrication cost offered by solution-based printing techniques. To enable the desired solubility/processability and carrier mobility, polymers are functionalized with hydrocarbon chains by strategically manipulating the alkylation patterns. Note that head-to-head (HH) linkages have traditionally been avoided because the induced backbone torsion leads to poor π–π overlap and amorphous film microstructures, and hence to low carrier mobilities. We report here the synthesis of a new building block for HH linkages, 4,4′-dialkoxy-5,5′-bithiazole (<b>BTzOR</b>), and its incorporation into polymers for high performance organic thin-film transistors. The small oxygen van der Waals radius and intramolecular S­(thiazolyl)···O­(alkoxy) attraction promote HH macromolecular architectures with extensive π-conjugation, low bandgaps (1.40–1.63 eV), and high crystallinity. In comparison to previously reported 3,3′-dialkoxy-2,2′-bithiophene (<b>BTOR</b>), <b>BTzOR</b> is a promising building block in view of thiazole geometric and electronic properties: (a) replacing (thiophene)­C–H with (thiazole)N reduces steric encumbrance in <b>–BTzOR–Ar–</b> dyads by eliminating repulsive C–H···H–C interactions with neighboring arene units, thereby enhancing π–π overlap and film crystallinity; and (b) thiazole electron-deficiency compensates alkoxy electron-donating characteristics, thereby lowering the <b>BTzOR</b> polymer HOMO versus that of the <b>BTOR</b> analogues. Thus, the new <b>BTzOR</b> polymers show substantial hole mobilities (0.06–0.25 cm²/(V s)) in organic thin-film transistors, as well as enhanced <i>I</i>_on:<i>I</i>_off ratios and greater ambient stability than the <b>BTOR</b> analogues. These geometric and electronic properties make <b>BTzOR</b> a promising building block for new classes of polymer semiconductors, and the synthetic route to <b>BTzOR</b> reported here should be adaptable to many other bithiazole-based building blocks

Extending Hexaazatriphenylene with Mono-/Bithiophenes in Acceptor–Donor Diads and Acceptor–Donor–Acceptor Triads

Three new hexaazatriphenylene (HAT)-based electron-accepting molecules with octupolar disc-like symmetry that combine the HAT core with six branches of electron-donor thiophenes in two modalities have been synthesized: (i) with six donor thiophenes and bithiophenes delineating a six-donor-to-one-acceptor (6–1) profile and (ii) with six donor–acceptor branches configuring a 6–6–1 acceptor–donor–acceptor triad. The 6-fold accumulation of donors and acceptors in the periphery of the HAT core is expected to tune the molecular electronic and optical properties. An exhaustive analysis of these properties as a function of the 6–1 and 6–6–1 stoichiometry of the molecules is described by combining a palette of experimental spectroscopic techniques such as electronic absorption (from the ground electronic and excited states), emission (fluorescence and phosphorescence), ultraviolet photoelectron spectroscopy, spectroelectrochemistry, and vibrational Raman have been implemented, all combined with electrochemistry and molecular theoretical modeling. A particular focus on the charged species and the charge distribution around the 6–1 and 6–6–1 patterns is conducted. Structure–property relationships have been outlined. The complete understanding of all these properties might help to design improved chromophores based on the HAT structure and to anticipate new properties

Synthesis of Perylene Imide Diones as Platforms for the Development of Pyrazine Based Organic Semiconductors

There is a great interest in peryleneimide (PI)-containing compounds given their unique combination of good electron accepting ability, high abosorption in the visible region, and outstanding chemical, thermal, and photochemical stabilities. Thus, herein we report the synthesis of perylene imide derivatives endowed with a 1,2-diketone functionality (<b>PIDs</b>) as efficient intermediates to easily access peryleneimide (PI)-containing organic semiconductors with enhanced absorption cross-section for the design of tunable semiconductor organic materials. Three processable organic molecular semiconductors containing thiophene and terthiophene moieties, <b>PITa</b>, <b>PITb</b>, and <b>PITT</b>, have been prepared from the novel <b>PIDs</b>. The tendency of these semiconductors for molecular aggregation have been investigated by NMR spectroscopy and supported by quantum chemical calculations. 2D NMR experiments and theoretical calculations point to an antiparallel π-stacking interaction as the most stable conformation in the aggregates. Investigation of the optical and electrochemical properties of the materials is also reported and analyzed in combination with DFT calculations. Although the derivatives presented here show modest electron mobilities of ∼10^–4 cm²V^–1s^–1, these preliminary studies of their performance in organic field effect transistors (OFETs) indicate the potential of these new building blocks as n-type semiconductors

Mobility versus Alignment of a Semiconducting π‑Extended Discotic Liquid-Crystalline Triindole

The p-type semiconducting properties of a triphenylene-fused triindole mesogen, have been studied by applying two complementary methods which have different alignment requirements. The attachment of only three flexible alkyl chains to the nitrogen atoms of this π-extended core is sufficient to induce columnar mesomorphism. High hole mobility values (0.65 cm² V^–1 s^–1) have been estimated by space-charge limited current (SCLC) measurements in a diode-like structure which are easily prepared from the melt, rendering this material a good candidate for OPVs and OLEDs devices. The mobility predicted theoretically via a hole-hopping mechanism is in very good agreement with the experimental values determined at the SCLC regime. On the other hand the hole mobility determined on solution processed thin film transistors (OFETs) is significantly lower, which can be rationalized by the high tendency of these large molecules to align on surfaces with their extended π-conjugated core parallel to the substrate as demonstrated by SERS. Despite the differences obtained with the two methods, the acceptable performance found on OFETs fabricated by simple drop-casting processing of such an enlarged aromatic core is remarkable and suggests facile hopping between neighboring molecular columns owing to the large conducting/isolating ratio found in this discotic compound

Bithiopheneimide–Dithienosilole/Dithienogermole Copolymers for Efficient Solar Cells: Information from Structure–Property–Device Performance Correlations and Comparison to Thieno[3,4‑<i>c</i>]pyrrole-4,6-dione Analogues

Rational creation of polymeric semiconductors from novel building blocks is critical to polymer solar cell (PSC) development. We report a new series of bithiopheneimide-based donor–acceptor copolymers for bulk-heterojunction (BHJ) PSCs. The bithiopheneimide electron-deficiency compresses polymer bandgaps and lowers the HOMOsessential to maximize power conversion efficiency (PCE). While the dithiophene bridge progression R₂Si→R₂Ge minimally impacts bandgaps, it substantially alters the HOMO energies. Furthermore, imide <i>N</i>-substituent variation has negligible impact on polymer opto-electrical properties, but greatly affects solubility and microstructure. Grazing incidence wide-angle X-ray scattering (GIWAXS) indicates that branched <i>N</i>-alkyl substituents increased polymer π–π spacings vs linear <i>N</i>-alkyl substituents, and the dithienosilole-based <b>PBTISi</b> series exhibits more ordered packing than the dithienogermole-based <b>PBTIGe</b> analogues. Further insights into structure–property–device performance correlations are provided by a thieno­[3,4-<i>c</i>]­pyrrole-4,6-dione (<b>TPD</b>)–dithienosilole copolymer <b>PTPDSi</b>. DFT computation and optical spectroscopy show that the <b>TPD</b>-based polymers achieve greater subunit–subunit coplanarity via intramolecular (thienyl)­S···O­(carbonyl) interactions, and GIWAXS indicates that <b>PBTISi-C8</b> has lower lamellar ordering, but closer π–π spacing than does the <b>TPD</b>-based analogue. Inverted BHJ solar cells using bithiopheneimide-based polymer as donor and PC₇₁BM as acceptor exhibit promising device performance with PCEs up to 6.41% and <i>V</i>_oc > 0.80 V. In analogous cells, the <b>TPD</b> analogue exhibits 0.08 V higher <i>V</i>_oc with an enhanced PCE of 6.83%, mainly attributable to the lower-lying HOMO induced by the higher imide group density. These results demonstrate the potential of <b>BTI</b>-based polymers for high-performance solar cells, and provide generalizable insights into structure–property relationships in <b>TPD</b>, <b>BTI</b>, and related polymer semiconductors