Tetraazahexacene Diimides with Ultralow Lowest Unoccupied Molecular Orbital Levels

Azaacene diimides are expected to possess deep lowest unoccupied molecular orbital (LUMO) levels and narrower bandgaps while maintaining excellent solubility and enhanced stability compared to their parent acenes. However, the synthesis of fully conjugated azaacenes has posed a long-term challenge. In this study, we report a stepwise oxidation approach to successfully synthesize a series of fully conjugated tetraazahexacene diimides (TAHDIs). Through periphery engineering, the targeted TAHDIs, featuring electron -donating ethylenedioxy rings, exhibited significantly enhanced stability, with a half-life time (tau 1/2) of up to 65 h under ambient conditions. Furthermore, single -crystal structural elucidation revealed a nearly planar geometry, with the imide rings slightly deviating from the skeleton plane. Notably, the LUMO levels were determined to be as low as -4.68 eV for TAHDI-ad and could be noticeably elevated to -4.53 eV through the attachment of electron -donating groups (TAHDI-ce). This work represents a rare example of an experimetally evidenced low-lying LUMO level, providing an alternative strategy for developing higher fully conjugated azacene diimides, which have great promise in electronics and molecular electronics.