Tether-entangled conjugated helices

A new design concept, tether-entangled conjugated helices (TECHs), is introduced for helical polyaromatic molecules. TECHs consist of a linear polyaromatic ladder backbone and periodically entangling tethers with the same planar chirality. By limiting the length of tether, all tethers synchronously bend and twist the backbone with the same manner, and change it into a helical ribbon with a determinate helical chirality. The 3D helical features are customizable via modular synthesis by using two types of synthons, the planar chiral tethering unit (C 2 symmetry) and the docking unit (C 2h symmetry), and no post chiral resolution is needed. Moreover, TECHs possess persistent chiral properties due to the covalent locking of helical configuration by tethers. Concave-type and convex-type oligomeric TECHs are prepared as a proof-of-concept. Unconventional double-helix π-dimers are observed in the single crystals of concave-type TECHs. Theoretical studies indicate the smaller binding energies in double-helix π-dimers than conventional planar π-dimers. A concentration-depend emission is found for concave-type TECHs, probably due to the formation of double-helix π-dimers in the excited state. All TECHs show strong circularly polarized luminescence (CPL) with dissymmetric factors (|g lum|) generally over 10-3. Among them, the (P)-T4-tBu shows the highest |g lum| of 1.0 × 10-2 and a high CPL brightness of 316 M-1 cm-1.

Recent Advances in Selenophene-Based Materials for Organic Solar Cells

Due to the low cost, light weight, semitransparency, good flexibility, and large manufacturing area of organic solar cells (OSCs), OSCs have the opportunity to become the next generation of solar cells in some specific applications. So far, the efficiency of the OSC device has been improved by more than 20%. The optical band gap between the lowest unoccupied molecular orbital (LUMO) level and the highest occupied molecular orbital (HOMO) level is an important factor affecting the performance of the device. Selenophene, a derivative of aromatic pentacyclic thiophene, is easy to polarize, its LUMO energy level is very low, and hence the optical band gap can be reduced. In addition, the selenium atoms in selenophene and other oxygen atoms or sulfur atoms can form an intermolecular interaction, so as to improve the stacking order of the active layer blend film and improve the carrier transport efficiency. This paper introduces the organic solar active layer materials containing selenium benzene in recent years, which can be simply divided into donor materials and acceptor materials. Replacing sulfur atoms with selenium atoms in these materials can effectively reduce the corresponding optical band gap of materials, improve the mutual solubility of donor recipient materials, and ultimately improve the device efficiency. Therefore, the sulfur in thiophene can be completely replaced by selenium or oxygen of the same family, which can be used in the active layer materials of organic solar cells. This article mainly describes the application of selenium instead of sulfur in OSCs.

Accessing the Ene-Imine Motif in 1H-Isoindole, Thienopyrrole, and Thienopyridine Building Blocks

A pathway to a range of diverse heterocycles was developed using a nucleophilic cyclization strategy. Lactams and ene-imines are accessed in a few steps from a common precursor, and these moieties are further elaborated to directly provide pyrroles or pyridines with extended conjugation. Reaction conditions are mild, and a broad range of structural types are available within a few steps.

New fused conjugated molecules with fused thiophene and pyran units for organic electronic materials

Rigid and planar conjugated molecules have substantial significance due to their potential applications in organic electronics. Herein we report two highly fused ladder type conjugated molecules, TTCTTC and TTTCTTTC, with up to 10 fused rings in which the fused-thiophene rings are fused to the chromeno[6,5,4-def]chromene unit. Both molecules show high HOMO levels and accordingly they can be oxidized into their radical cations with absorptions extending to 1300 nm in the presence of trifluoroacetic acid. Thin films of TTCTTC and TTTCTTTC exhibit p-type semiconductor properties with hole mobilities up to 0.39 cm² V⁻¹ s⁻¹. Moreover, TTCTTC shows a high fluorescence quantum yield of up to 16.5% in the solid state.

Fused conjugated molecules TTCTTC and TTTCTTTC with up to ten heterocycles were constructed by fusing fused-thiophene to the chromeno[6,5,4-def]chromene unit.

Recent Advances in Wide-Bandgap Photovoltaic Polymers

The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials.

Accessing pyrrolones and pyridinones: controlling 5-exo and 6-endo ring closures in heterocyclic alkynylamides

Competitive 5-exo and 6-endo anionic intramolecular cyclization reactions in heterocyclic alkynylamides were explored via experimental and computational analysis. The 5-exo-dig cyclization pathway is usually disfavoured in heterocyclic systems, and 6-endo products are often both the kinetic and thermodynamic products. However, we’ve found that it is possible to shift selectivity toward the 5-exo-dig pyrrolone products away from the less strained pyridinone products that are produced via the 6-endo-dig cyclization. Parameters such as identity of heteroatom, heteroatom positioning within the heterocycle, and functionality on the alkyne were investigated and, in many cases, were found to strongly influence product ratios. A series of computational studies was performed to provide further insight into the 5-exo-dig and 6-endo-dig pathways in these heterocyclic systems. Theoretical predictions were found to reproduce experimental results, highlighting the predictive capabilities of the computations in determining preferred products.

D–A copolymers with the benzo[1,2-b:4,5-c′]dithiophene-4,8-dione acceptor unit for polymer solar cells

D–A copolymers with the benzo[1,2-b:4,5-c′]dithiophene-4,8-dione acceptor unit and the thiophene or thieno[3,2-b]thiophene donor unit were developed. PThBDTD:PC₇₁BM and PTTBDTD:PC₇₁BM solar cells gave PCEs of 6.32% and 6.00%, respectively.

The effect of fluorination on the photovoltaic performance of the D–A copolymers containing naphtho[2,3-c]thiophene-4,9-dione and bithiophene moieties

Fluorine improves the planarity of the polymer backbone via its lock-up function. Polymer PFNTDFBT shows a high mobility and its solar cells gave a PCE of 7.79%.

Influence of aromatic heterocycle of conjugated side chains on photovoltaic performance of benzodithiophene-based wide-bandgap polymers

The influence of conjugated side chains on photovoltaic performance of benzodithiophene-based wide-bandgap polymers is studied by traversing chalcogen heterocycles.

A pentacyclic building block containing an azepine-2,7-dione moiety for polymer solar cells

A pentacyclic building block containing an azepine-2,7-dione moiety (TTA) was developed. PTTABDT:PC₇₁BM solar cells gave a higher PCE of 5.46%, resulting from higherV_ocand ideal morphology.

A simple strategy to the side chain functionalization on the quinoxaline unit for efficient polymer solar cells

A new tetrafluoridequinoxaline electron accepting block-ffQx from a quinoxaline core was designed. A new copolymer (PBDTT-ffQx) was synthesized from tetrafluoridequinoxaline and benzodithiophene and a high PCE of 8.6% was obtained.

Comparison of selenophene and thienothiophene incorporation into pentacyclic lactam-based conjugated polymers for organic solar cells

In this work, we compare the effect of incorporating selenophene versus thienothiophene spacers into pentacyclic lactam-based conjugated polymers for organic solar cells.