Pyrrole[3,2-d:4,5-d′]bisthiazole-bridged bis(naphthalene diimide)s as electron-transport materials

Abstract

A series of materials with 2,6-disubstituted-N-alkyl-pyrrole[3,2-d:4,5-d′]bisthiazole (PBTz) with triisopropylsilyl- (TIPS), bromo- and naphthalene diimide (NDI) groups were synthesized. The electronic properties of 2,6-bis-TIPS- and 2,6-dibromo-N-hexyl-PBTz were studied by cyclic voltammetry and by density functional theory (DFT) calculations, and their solid-state packing was examined by the single crystal X-ray structural analysis. DFT calculations and the electrochemical data revealed that this core is both a weak donor and a weak acceptor. Small molecules with bis(NDI)-substituted N-alkyl-PBTz architecture were studied by differential pulse voltammetry, UV-vis absorption spectroscopy, and differential scanning calorimetry, and their electrical properties were examined in n-channel organic field-effect transistors using solution-processed films. The electron mobility value μ_e as high as 0.13 cm² V⁻¹ s⁻¹ with a I_on/I_off ratio of 5 × 10⁵ and threshold voltage V_th = 4.9 V was observed for PBTz-bridged bis(naphthalene diimide) with hexyl chains on pyrrole and NDI nitrogen atoms, while the material with longer dodecyl groups showed μ_e up to 0.19 cm² V⁻¹ s⁻¹ with a I_on/I_off ratio of 7 × 10⁴ and V_th = 7.9 V in a 1 : 1 polystyrene matrix. Finally, compounds with electron-withdrawing acetyl groups at position 6 of the NDI units were examined by electrochemistry and in OFET configurations.