High Thermally Stable n‑Type Semiconductor up to 850 K Based on Dianionic Naphthalenediimide Derivative

Electrostatic cation–anion interaction is effective to form a tightly bounded π-molecular assembly, which enhances the thermal stability and carrier transport property. Dianionic bis­(benzenesulfonate)–naphthalenediimide (BSNDI^2–) formed simple 2:1 cation–anion pairs of (Na⁺)₂(BSNDI^2–) (1), (K⁺)₂(BSNDI^2–) (2), and (NH₄⁺)₂(BSNDI^2–) (3), and their redox behaviors, thermal stabilities, crystal structures, electron transport properties, and dielectric constants were compared to those of neutral bis­(phenyl)–naphthalenediimide (4). Crystals 1, 2, and 3 had quite high thermal stabilities up to 850, 810, and 600 K, respectively, even though organic molecules. A two-dimensional (2D) n-type electron transport layer consisting of NDI π cores was sandwiched between networks of highly polarized electrostatic cation–anion pairs showing 2D herringbone (1), one-dimensional π-stacking (2), and brickstone-like 2D π-stacking (3) interactions. The values of electron mobility in polycrystalline 1, 2, 3, and 4 reached 0.22, >0.0003, 0.036, and >0.028 cm² V^–1 s^–1, respectively, according to flash-photolysis time-resolved microwave conductivity measurements. The electron mobility of crystal 1 was 1 order of magnitude higher than those of crystals 2, 3, and 4 owing to the tight intermolecular interactions within the 2D transport layer. The real part dielectric constants of crystals 1, 2, 3, and 4 were ∼4, ∼50, ∼20, and ∼4 at 450 K, respectively, which affected the electron transport property. The chemical design of highly polarized electrostatic cation–anion pair formed the 2D transport layer and also has high thermal stability up to ∼850 K in the ionic n-type semiconducting materials.