Dicyanomethylene-quinoid vs. dicyanovinyl-benzenoid organic semiconductors: Understanding structure-property correlations in mesomerism-like forms

• Two mesomerism-like forms based on BDT units are synthesized.
• DCM-Q-BDT has higher electron mobility and better air stability than DCV-B-BDT.
• We demonstrated experimentally physical and electronic properties of two n-type small molecules.

Understanding two mesomerism-like forms (quinoid vs. benzenoid structures) over organic semiconductors (OSCs) is essential for achieving high electronic device performance. Herein, we report the synthesis as well as the comparative physicochemical, microstructural, and charge-transporting analysis of dicyanomethylene-quinoid versus dicyanovinyl-benzenoid OSCs based on benzo[1,2-b:4,5-b′]dithiophene (BDT) units (DCM-Q-BDT and DCV-B-BDT). The electron-deficient nature of the quinoid structure in DCM-Q-BDT can lower the LUMO level and bandgap relative to the benzenoid analogy DCV-B-BDT. Top-gate/bottom-contact (TG/BC) field-effect transistors (OFETs) based on DCM-Q-BDT show not only the maximum electron mobility up to 0.23 cm2/V.s without requiring post-annealing treatments, but also demonstrate excellent air stability (half-life times of drain current ≈ 35 h) without any encapsulation. The superior n-channel performance for DCM-Q-BDT is due to the anisotropic orientation, high degree of the crystallinity, and low-lying LUMO induced by the quinoid structure. Our study shows underlying structure–property relationships in quinoid over benzenoid OSCs while demonstrating promise in n-channel OFETs.

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