Tetraazahexacene Diimides with Ultralow LUMO Levels

Abstract

Azaacene diimides are expected to possess deep LUMO levels and narrower band gaps 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 of up to 65 h under ambient conditions. Furthermore, single-crystal structural elucidation revealed the nearly planar geometry, with 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.

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