Ladder‐type Heteroarenes: Up to 15 Rings with Five Imide Groups

Dithienothiapyran: An Excellent Donor Block for Building High-Performance Copolymers in Nonfullerene Polymer Solar Cells

In this work, a new but excellent donor block dithienothiapyran (DTTP) was developed for constructing highly efficient wide band gap copolymer donors. Compared to dithienopyran (DTP), DTTP features weaken electron-donating ability and more planar-conjugated backbones. Polymer-fluorinated benzotriazole (FBTA) based on DTTP exhibits lower highest occupied molecular orbital level (-5.30 vs -5.21 eV), higher molar extinction coefficient (1.54 × 10⁵ vs 8.65 × 10⁴ M^-1 cm^-1), and better crystallinity than -FBTA based on DTP, thus producing a higher device performance of 10.51% in binary blend nonfullerene polymer solar cells (NF-PSCs) blended with IT-M. To improve the absorption strength of PDTTP-FBTA: devices in the shorter wavelength range and further optimize the blend morphology, a small molecule of , which has strong absorption at short wavelength (300-600 nm), was incorporated. Finally, the performance of the ternary blends was successfully enhanced to 11.57% and a very high fill factor of 76.5%. Our work provided a new but excellent donor block for building high-performance conjugated copolymers to achieve highly efficient NF-PSCs.

Extraordinary Redox Activities in Ladder-Type Conjugated Molecules Enabled by B ← N Coordination-Promoted Delocalization and Hyperconjugation

The introduction of B ← N coordinate bond-isoelectronic to C-C single bond-into π-systems represents a promising strategy to impart exotic redox and electrochromic properties into conjugated organic molecules and macromolecules. To achieve both reductive and oxidative activities using this strategy, a cruciform ladder-type molecular constitution was designed to accommodate oxidation-active, reduction-active, and B ← N coordination units into a compact structure. Two such compounds (BN-F and BN-Ph) were synthesized via highly efficient N-directed borylation. These molecules demonstrated well-separated, two reductive and two oxidative electron-transfer processes, corresponding to five distinct yet stable oxidation states, including a rarely observed boron-containing radical cation. Spectroelectrochemical measurements revealed unique optical characteristics for each of these reduced/oxidized species, demonstrating multicolor electrochromism with excellent recyclability. Distinct color changes were observed between each redox state with clear isosbestic points on the absorption spectra. The underlying redox mechanism was elucidated by a combination of computational and experimental investigations. Single-crystal X-ray diffraction analysis on the neutral state, the oxidized radical cation, and the reduced dianion of BN-Ph revealed structural transformations into two distinct quinonoid constitutions during the oxidation and reduction processes, respectively. B ← N coordination played an important role in rendering the robust and reversible multistage redox properties, by extending the charge and spin delocalization, by modulating the π-electron density, and by a newly established hyperconjugation mechanism.

Drastic Effects of Fluorination on Backbone Conformation of Head-to-Head Bithiophene-Based Polymer Semiconductors

This study shows that the backbone conformation of head-to-head type 3,3'-dialkyl-2,2'-bithiophene can be tuned via fluorination of the neighboring benzothiadiazole (BTz). Without fluorination, the polymer backbone is highly twisted, whereas difluorination of BTz produced a coplanar backbone. Monofluorination of BTz yielded a tunable polymer backbone conformation depending on the film annealing temperature. In organic thin-film transistors, the polymer with the head-to-head linkages showed a remarkable hole mobility of >0.5 cm² V^-1 s^-1 upon attaining a planar backbone. Thus, the head-to-head linkage does not necessarily lead to backbone nonplanarity, and achieving planar conformation of 3,3'-dialkyl-2,2'-bithiophene has profound implications in materials design for organic semiconducting devices, yielding good solubility, reduced materials synthetic steps, and improved opto-electrical properties.

Fused Isoindigo Ribbons with Absorption Bands Reaching Near-Infrared

Through fusing isoindigo (IID) units at 6,7;6',7'-positions, a series of new near-infrared (NIR) absorbing and stable ribbon-like conjugated molecules, namely nIIDs in which n represents the number of IID units, have been synthesized. The optical band gaps of the molecules are lowered from 2.03 eV of 1IID to 1.12 eV of 6IID with the increase of the conjugation length. 3IID, 4IID, and 6IID have strong absorption in the NIR region and exhibit photothermal conversion efficiencies of greater than 50 % under laser irradiation at λ=808 nm.

Dibenzothienopyrrolo[3,2-b]pyrrole: The Missing Member of the Thienoacene Family

Dibenzothienopyrrolo[3,2-b]pyrrole and the corresponding bis(S,S-dioxide) were synthesized by using a concise synthetic strategy. Despite the presence of six fused aromatic rings, π-expanded pyrrolo[3,2-b]pyrroles of this type absorb and emit at relatively short wavelengths, which reflects inefficient π conjugation due to the angular arrangement of the aromatic rings. They exhibit interesting and complex electrochemical behavior, which highlights their potential in organic electronics. Both heteroacenes undergo two-stage oxidation while retaining the independence of each 1-phenyl-1H-[1]benzothieno[3,2-b]pyrrole, which was proved by in situ electron spin resonance measurements. Interestingly, electrochemically generated dicationdiradicals are not only distributed over the pyrrolo[3,2-b]pyrrole scaffold, but also over the phenyl substituents located on nitrogen atoms.

An Imide-Based Pentacyclic Building Block for n-Type Organic Semiconductors

A new electron-deficient unit with a fused 5-membered heterocyclic ring was developed by replacing a cyclopenta-1,3-diene from electron-rich donor indacenodithiophene (IDT) with a cyclohepta-4,6-diene-1,3-diimde unit. The imide bridge endows dithienylbenzenebisimide (BBI) with a fixed planar configuration and low energy levels for both the highest occupied molecular orbital (HOMO; -6.24 eV) and the lowest unoccupied molecular orbit (LUMO; -2.57 eV). Organic field-effect transistors (OFETs) based on BBI polymers exhibit electron mobility up to 0.34 cm²  V^-1  s^-1 , which indicates that the BBI is a promising n-type building block for optoelectronics.

Extended Ladder-Type Benzo[k]tetraphene-Derived Oligomers

Well-defined, fused-ring aromatic oligomers represent promising candidates for the fundamental understanding and application of advanced carbon-rich materials, though bottom-up synthesis and structure-property correlation of these compounds remain challenging. In this work, an efficient synthetic route was employed to construct extended benzo[k]tetraphene-derived oligomers with up to 13 fused rings. The molecular and electronic structures of these compounds were clearly elucidated. Precise correlation of molecular sizes and crystallization dynamics was established, thus demonstrating the pivotal balance between intermolecular interaction and molecular mobility for optimized processing of highly ordered solids of these extended conjugated molecules.