Synthesis and Characterization of 5-Octylthieno[3,4-c]pyrrole-4,6-dione Derivatives As New Monomers for Conjugated Copolymers

A Four-Component Reaction for the Synthesis of Thienopyrrolediones under Transition Metal Free Conditions

A three-starting-material four-component reaction strategy is described to construct thienopyrrolediones (TPDs) from the simplest raw materials, elemental sulfur, aldehydes, and β-ketoamides, under transition metal free conditions. Compared with traditional multistep reaction sequences, this process is simple, efficient, environmentally friendly, and atom-economic and has laid the foundation for further development of an easily synthesized TPD unit.

Acceptor Modulation Strategies for Improving the Electron Transport in High-Performance Organic Field-Effect Transistors

High-performance ambipolar and electronic type semiconducting polymers are essential for fabricating various organic optoelectronic devices and complementary circuits. This review summarizes the strategies of improving the electron transport of semiconducting polymers via acceptor modulation strategies, which include the use of single, dual, triple, multiple, and all acceptors as well as the fusion of multiple identical acceptors to obtain new heterocyclic acceptors. To further improve the electron transport of semiconducting polymers, the introduction of strong electron-withdrawing groups can enhance the electron-withdrawing ability of donors and acceptors, thereby facilitating electron injection and suppressing hole accumulation. In addition, the relationships between the molecular structure, frontier molecular orbital energy levels, thin film morphology, microstructure, processing conditions, and device performances are also comprehensively discussed. Finally, the challenges encountered in this research area are proposed and the future outlook is presented.

Scaffold Hopping Strategy to Identify Prostanoid EP4 Receptor Antagonists for Cancer Immunotherapy

Cancer cells can effectively suppress the natural immune response in humans, and prostaglandin E₂ (PGE₂) is a key mediator in the development of tumor cell resistance to immunotherapy. As a major contributor to PGE₂-elicited immunosuppressive activity, the EP4 receptor promotes tumor development and progression in the tumor microenvironment, and the development of selective and potent EP4 receptor antagonists should have promising potential for tumor immunotherapy. Aiming at improving the drug-like properties, a series of 4,7-dihydro-5H-thieno[2,3-c]pyran derivatives were designed and synthesized through a scaffold hopping strategy. The most promising compound 47 exhibited good EP4 antagonistic activity and excellent subtype selectivity, as well as favorable drug-like properties. It effectively suppressed the expression of multiple immunosuppression-related genes in macrophages. Meanwhile, oral administration of compound 47, alone or in combination with anti-PD-1 antibody, significantly enhanced the antitumor immune response and inhibited tumor growth in the mouse CT26 colon carcinoma model.

Molecular Weight Engineering in High-Performance Ambipolar Emissive Mesopolymers

Mesopolymers with high solubility, free of structural defects, and negligible batch-to-batch variation open a new avenue for organic optoelectronics. Organic light emitting transistors that combine the functions of organic light-emitting diodes and organic field-effect transistors. However, charge transport ability and light emitting strength are contradictory within one conjugated polymer. Herein, three low-molecular-weight mesopolymers with thienopyrroledione-benzothiadiazole repeating units (meso-TBTF) were obtained. The mesopolymers show strong solid-state emission and high ambipolar carrier mobility. The molecular weights of meso-TBTF can be tuned by polymerization temperature. The mesopolymers have photoluminescence quantum yields (PLQY) of about 50 % in solution and 10 % in solid state. Polymer light emitting diodes of this material are fabricated to explore its potential use in optoelectronic devices.

Capturing Mobile Lithium Ions in a Molecular Hole Transporter Enhances the Thermal Stability of Perovskite Solar Cells

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3-bis(5-(4-(bis(4-methoxyphenyl) amino)phenyl)thieno[3,2-b]thiophen-2-yl)-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (coded HL38) is reported. Hole mobility of 1.36 × 10^-3 cm² V^-1 s^-1 and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine as additives. Interface engineering with 2-(2-aminoethyl)thiophene hydroiodide (2-TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive-containing 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD)-based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38-based PSC retains 85.9% of the initial PCE, while the spiro-MeOTAD-based PSC degrades unrecoverably from 21.1% to 5.8%. Time-of-flight secondary-ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro-MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole-transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non-conventional MHTs.

From Red to Green Luminescence via Surface Functionalization. Effect of 2-(5-Mercaptothien-2-yl)-8-(thien-2-yl)-5-hexylthieno[3,4-c]pyrrole-4,6-dione Ligands on the Photoluminescence of Alloyed Ag-In-Zn-S Nanocrystals

A semiconducting molecule containing a thiol anchor group, namely 2-(5-mercaptothien-2-yl)-8-(thien-2-yl)-5-hexylthieno[3,4-c]pyrrole-4,6-dione (abbreviated as D-A-D-SH), was designed, synthesized, and used as a ligand in nonstoichiometric quaternary nanocrystals of composition Ag_1.0In_3.1Zn_1.0S_4.0(S_6.1) to give an inorganic/organic hybrid. Detailed NMR studies indicate that D-A-D-SH ligands are present in two coordination spheres in the organic part of the hybrid: (i) inner in which the ligand molecules form direct bonds with the nanocrystal surface and (ii) outer in which the ligand molecules do not form direct bonds with the inorganic core. Exchange of the initial ligands (stearic acid and 1-aminooctadecane) for D-A-D-SH induces a distinct change of the photoluminescence. Efficient red luminescence of nanocrystals capped with initial ligands (λ_max = 720 nm, quantum yield = 67%) is totally quenched and green luminescence characteristic of the ligand appears (λ_max = 508 nm, quantum yield = 10%). This change of the photoluminescence mechanism can be clarified by a combination of electrochemical and spectroscopic investigations. It can be demonstrated by cyclic voltammetry that new states appear in the hybrid as a consequence of D-A-D-SH binding to the nanocrystals surface. These states are located below the nanocrystal LUMO and above its HOMO, respectively. They are concurrent to deeper donor and acceptor states governing the red luminescence. As a result, energy transfer from the nanocrystal HOMO and LUMO levels to the ligand states takes place, leading to effective quenching of the red luminescence and appearance of the green one.

Influence of Bridging Groups on the Photovoltaic Properties of Wide-Bandgap Poly(BDTT- alt-BDD)s

To further advance polymer solar cells requires the fast evolution of π-conjugated materials as well as a better understanding of their structure-property relationships. Herein, we present three copolymers (PT1, PT2, PT3) made through tuning π-bridges (without any group, thiophene, and 3-hexylthieno[3,2- b]thiophene) between electron-rich (D: BDTT) and -deficient (A: BDD) units. The comparative studies reveal the unique correlation that the tune of π-bridge on the polymeric backbone governs the solid stacking and photovoltaic properties of resultant poly(BDTT- alt-BDD)s, which provide an effective way to deliver new and efficient polymer with feasible processability. That is, polymers with either twist zigzag backbone (PT1) or with linear coplanar backbone (PT2) result in inferior photovoltaic performance upon simple solution casting. Among them, PT3 with extended zigzag backbone and planar segments exhibits suitable processability and retains good efficiency in nonfullerene solar cells through a single-solvent cast without involving tedious treatments. This work illustrates that the tuning of the D-π-A polymer backbone facilitates efficient materials with feasible processability, promising for scale-up fabrication.

Efficient Near-Infrared Electroluminescence at 840 nm with "Metal-Free" Small-Molecule:Polymer Blends

Due to the so-called energy-gap law and aggregation quenching, the efficiency of organic light-emitting diodes (OLEDs) emitting above 800 nm is significantly lower than that of visible ones. Successful exploitation of triplet emission in phosphorescent materials containing heavy metals has been reported, with OLEDs achieving remarkable external quantum efficiencies (EQEs) up to 3.8% (peak wavelength > 800 nm). For OLEDs incorporating fluorescent materials free from heavy or toxic metals, however, we are not aware of any report of EQEs over 1% (again for emission peaking at wavelengths > 800 nm), even for devices leveraging thermally activated delayed fluorescence (TADF). Here, the development of polymer light-emitting diodes (PLEDs) peaking at 840 nm and exhibiting unprecedented EQEs (in excess of 1.15%) and turn-on voltages as low as 1.7 V is reported. These incorporate a novel triazolobenzothiadiazole-based emitter and a novel indacenodithiophene-based transport polymer matrix, affording excellent spectral and transport properties. To the best of knowledge, such values are the best ever reported for electroluminescence at 840 nm with a purely organic and solution-processed active layer, not leveraging triplet-assisted emission.

Copper catalyzed synthesis of conjugated copolymers using direct arylation polymerization

As an effort to replace palladium catalysts, we report the first example of a Copper-catalyzed Direct Arylation Polymerization (DArP).

Highly efficient polymer solar cells with a thienopyrroledione and benzodithiophene containing planar random copolymer

A new random copolymer based on thienopyrroledione and benzodithiophene units with a high degree of planarity was developed for high-performance organic solar cells.

Bithienopyrroledione vs. thienopyrroledione based copolymers: dramatic increase of power conversion efficiency in bulk heterojunction solar cells

Bithienopyrroledione (bi-TPD) based polymers P1 and P2 are designed and synthesized.

High performance thin film transistors based on bi-thieno[3,4-c]pyrrole-4,6-dione-containing copolymers: tuning the face-on and edge-on packing orientations

The tuning of face-on and edge-on packing structures of TPD-containing copolymers was achieved and the relationship between the packing structures and device performance was investigated.

A conformational locking strategy in linked-acceptor type polymers for organic solar cells

The concept of introducing intramolecular noncovalent conformational locks into the polymer main chain was implemented to improve the coplanarity of the linked-acceptor polymers. As a result, the novel polymer shows the best power conversion efficiency of 8.18%.

Linked-Acceptor Type Conjugated Polymer for High Performance Organic Photovoltaics with an Open-Circuit Voltage Exceeding 1 V

A linked-acceptor type conjugated polymer is designed and sythesized based on 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (BDTT) and linked-thieno[3,4-c]pyrrole-4,6-dione (LTPD). This polymer uses alkyl-substituted thiophene as a bridge. The PBDTT-LTPD includes two TPD units in one repeating unit, which can enhance acceptor density in the polymer backbone and lower the highest occupied molecular orbital (HOMO) level. By contrast, variable alkyl substitutions in the thiophene-bridges ensure the subtle regulation of polymer properties. The solar cells based on PBDTT-LTPD display an open-circuit voltage (Voc) that exceeds 1 V, and a maximum power conversion efficiency (PCE) of 7.59% is obtained. This PCE value is the highest for conventional single-junction bulk heterojunction solar cells with Voc values of up to 1 V. Given that PBDTT-LTPD exhibits a low HOMO energy level and a band gap equivalent to that of poly(3-hexylthiophene), PBDTT-LTPD/phenyl-C61-butyric acid methyl ester may be a promising candidate for the front cell in tandem polymer solar cells.

Small molecules based on thieno[3,4-c]pyrrole-4,6-dione for high open-circuit voltage (VOC) organic photovoltaics: effect of different positions of alkyl substitution on molecular packing and photovoltaic performance

Two different thienopyrroledione (TPD)-based small molecules (SMs) with different alkyl substitution positions were synthesized, and their photovoltaic properties are measured and compared to examine the effect of the alkyl substitution position on their optical, electrochemical, and photovoltaic properties. The use of TPD as an electron-accepting unit in conjugated SMs effectively lowers the highest occupied molecular orbital (HOMO) energy levels of the conjugated SMs and leads to high open-circuit voltage (VOC). The two SMs with n-hexyl group substituted at different positions exhibit almost identical optical and electrochemical properties in the pristine state. However, the crystallographic and morphological characteristics of the two SMs are significantly different, because they are blended with PC71BM. The SM in which n-alkyl groups are substituted at the central accepting unit exhibits a power conversion efficiency (PCE) of 6.0% with VOC=0.94 V, which is among the highest PCE values of TPD-based SM devices, whereas the SM with n-alkyl groups being substituted at the chain ends shows a moderate PCE value of 3.1%.

Semi-random vs Well-Defined Alternating Donor-Acceptor Copolymers

The influence of backbone composition on the physical properties of donor-acceptor (D-A) copolymers composed of varying amounts of benzodithiophene (BDT) donor with the thienoisoindoledione (TID) acceptor is investigated. First, the synthesis of bis- and tris-BDT monomers is reported; these monomers are subsequently used in Stille copolymerizations to create well-defined alternating polymer structures with repeating (D-A), (D-D-A), and (D-D-D-A) units. For comparison, five semi-random D-A copolymers with a D:A ratio of 1.5, 2, 3, 4, and 7 were synthesized by reacting trimethyltin-functionalized BDT with various ratios of iodinated BDT and brominated TID. While the HOMO levels of all the resultant polymers are very similar, a systematic red shift in the absorbance spectra onset of the D-A copolymer films from 687 to 883 nm is observed with increasing acceptor content, suggesting the LUMO can be fine-tuned over a range of 0.4 eV. When the solid-state absorbance spectra of well-defined alternating copolymers are compared to those of semi-random copolymers with analogous D:A ratios, the spectra of the alternating copolymers are significantly more red-shifted. Organic photovoltaic device efficiencies show that the semi-random materials all outperform the well-defined alternating copolymers, and an optimal D:A ratio of 2 produces the highest efficiency. Additional considerations concerning fine-tuning the lifetimes of the photoconductance transients of copolymer:fullerene films measured by time-resolved microwave conductivity are discussed. Overall, the results of this work indicate that the semi-random approach is a powerful synthetic strategy for fine-tuning the optoelectronic and photophysical properties of D-A materials for a number of systematic studies, especially given the ease with which the D:A ratios in the semi-random copolymers can be tuned.