Isomerically Pure Oxindole‐Terminated Quinoids for n‐Type Organic Thin‐Film Transistors Enabled by the Chlorination of Quinoidal Core

Abstract

Quinoidal compounds have great potential utility as high‐performance organic semiconducting materials because of their rigid planar structures and extended π‐conjugation. However, the existence of E and Z isomers adversely affects the charge‐transport properties of quinoidal compounds. In this study, three isomerically pure oxindole‐terminated quinoids were developed by introducing chlorine atoms in the quinoidal core. The synthesized quinoids were confirmed to have a Z,Z configuration by means of 1H NMR spectroscopy, density functional theory calculations, and single‐crystal X‐ray analysis. Importantly, the strategy of chlorination allowed to maintain low‐lying frontier molecular orbital energy levels and ensure favorable intermolecular packing. Consequently, all three quinoidal compounds showed n‐type transport characteristics in organic thin‐film transistors, with electron mobilities up to 0.35 cm2 V−1 s−1, which is the highest value reported to date for oxindole‐terminated quinoids. Our study can provide new guidelines for the design of isomerically pure quinoids with high electron mobilities.

Convergent Synthesis of the Precursors to Thiophene-Based Quinoids

“…Like thiophene-based quinoids reported in the literature, , configurational isomers were also observed in our research. Previous reports have shown that these isomers can be interconverted via diradical intermediates, and the isomerization process can be controlled by introducing steric repulsion or intramolecular noncovalent interactions. , Indeed, after exerting steric effects by incorporating an alkyl or alkoxy substituent on the thiophene ring, we found the isomers of our synthesized quinoids changed significantly. For example, three isomers, Q1-a ( E,E ), Q1-b ( Z,E ), and Q1-c ( Z , Z ), were observed in Q1 , with an approximately 2:2:1 ratio as estimated from integration of the respective resonance in the 1 H NMR spectrum (Figure S1), whereas Q2 showed only E , E and Z , E isomers with a ratio of 7:1 (Figure S2).…”

Recent Research Progress in Indophenine-Based-Functional Materials: Design, Synthesis, and Optoelectronic Applications

“…p-type semiconductors compound 14 exhibited excellent unipolar hole mobility up to 0.15 cm 2 V −1 s −1 . Geng’s group further proposed the chlorination strategy for the conformation of the locked indophenine derivatives [ 51 ]. The energy gap among 7a – 7c was determined by DFT calculations to be less than 1 kcal/mol, and this variation was significantly enhanced by the insertion of a chlorine atom.…”

“…As previously discussed, the contact of S⋯O highlights the role of intramolecular non-covalent interactions in the conformational lock. The role of intramolecular interactions to induce conformational lock was further demonstrated in di-chlorinated bithiophene bridge in indophenine (compounds 15a–c ) [ 51 ]. The presence of intramolecular Cl⋯H and S⋯O non-covalent interactions in Figure 16 h contributes to the stabilization of the Z , Z conformation.…”