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 πcores 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.