4nπ Stable Multitasking Azapentacene: Acidochromism, Hole Mobility, and Visible Light Photoresponse

Herein, we describe the synthesis, characterization, and optoelectronic investigation of a stable 4nπ dihydrotetraazapentacene derivative. The neutral dihydrotetraazapentacene contains a 24π-conjugated N-heteroacene core with two phenyl pendants appended thereof. The exceptional stability of this formally antiaromatic π-system is attributed to the fused dihydropyrazine ring, which has ethenamine (enamine) conjugations, and hence, the π-electrons delocalize over the nearly planar azapentacene core to endow with a global aromatic characteristic. The embedded dihydropyrazine also offers an additional Clar’s sextet with enhanced aromaticity. The present dihydrotetraazapentacene can be considered as a multitasking N-heteroacene, which showed photoresponsive nature under visible light illumination, acidochromism in solution, and p-type charge transport with an appreciable field-effect hole mobility of 0.02 cm2 V–1 s–1 and a bulk p-type mobility of 0.98 × 10–4 cm2 V–1 s–1 in the space charge-limited regime of operation measured in the hole-only device. Nucleus-independent chemical shift calculation, anisotropy of the induced current density plot, and anisotropic mobility calculation were performed to support the experimental findings.

本文报道了一种稳定的4nπ型二氢四氮并五苯衍生物的合成、表征及光电性能研究。该中性二氢四氮并五苯含有一个24π共轭的氮杂并苯（N-heteroacene）母核，其上连有两个苯基侧基。该形式上属于反芳香性的π体系所具备的优异稳定性，源于其稠合的二氢吡嗪环所具有的烯胺（ethenamine）共轭结构；因此π电子可在近乎平面的氮杂并五苯母核上离域，赋予体系全局芳香性特征。嵌入的二氢吡嗪环还可提供额外的克拉六重态（Clar’s sextet），进一步提升体系芳香性。本研究中的二氢四氮并五苯可被视为一种多功能氮杂并苯，其在可见光照射下表现出光响应特性，在溶液中呈现酸致变色行为；同时具备p型电荷传输性能：在空穴单极器件测试的空间电荷限制传输区下，其场效应空穴迁移率可达0.02 cm²·V⁻¹·s⁻¹，体相p型迁移率为0.98 × 10⁻⁴ cm²·V⁻¹·s⁻¹。通过核独立化学位移（Nucleus-independent chemical shift, NICS）计算、感应电流密度各向异性（anisotropy of the induced current density, AICD）作图及各向异性迁移率计算，佐证了实验结果。