Dually Switchable Heterotetracenes: Addressing the Photophysical Properties and Self-Organization of the P−S System

New ladder-type, phosphorus- and sulfur-based heterotetracenes were synthesized, which allowed the engineering of the materials’ properties by exploitation of the different reactivities between sulfur and phosphorus. 31P NMR spectroscopy and X-ray crystallographic studies revealed that the different electronic effects of the secondary heteroatom, sulfur, influence not only the conjugation in the heterotetracene core but also the behavior of the phosphorus center. UV−vis and fluorescence spectroscopy showed that the scaffold’s band gap is mainly controlled by the electronic nature of sulfur, while the fluorescence quantum yield highly depends on the electronic nature of phosphorus. Cyclic voltammetry indicated that the redox properties of the system could be altered by selective modification of the respective heteroatom (oxidation of sulfur and/or functionalization of trivalent phosphorus). Importantly, oxidation of the phosphorus center results in enhanced reduction features of the heterotetracene system, and oxidation of the sulfur center further enhances the electron acceptor character of the core. Theoretical calculations provided insights on both selectivity of phosphorus chemistry and communication between the two heteroatoms (sulfur and phosphorus). Macroscopic self-organization of the heterotetracenes was observed when the tetracene core is functionalized with pendant functional groups. Preliminary results showed that extension of the molecule with an alkyl chain along the long axis of molecules induces the formation of 1D microfibers, which was confirmed by fluorescence microscopy and scanning electron microscopy.本研究合成了一类新型含磷与硫的梯型杂并四苯，可通过利用硫与磷间的反应活性差异，实现材料性能的精准调控。通过31P核磁共振波谱（31P NMR）与X射线晶体学研究发现，次要杂原子硫所带来的不同电子效应，不仅会影响杂并四苯核心的共轭结构，还会改变磷中心的行为特性。紫外-可见（UV-vis）吸收光谱与荧光光谱分析显示，该骨架的带隙主要由硫的电子特性决定，而荧光量子产率则高度依赖于磷的电子特性。循环伏安法测试表明，通过对相应杂原子进行选择性修饰（如硫的氧化、三价磷的官能化），可调控该体系的氧化还原特性。尤为关键的是，磷中心的氧化会强化杂并四苯体系的还原特性，而硫中心的氧化则进一步提升了核心的电子受体能力。理论计算为磷化学的选择性调控以及两种杂原子（硫与磷）间的电子耦合效应提供了理论见解。当并四苯核心接枝悬挂官能团时，可观察到这类杂并四苯的宏观自组装行为。初步研究结果显示，沿分子长轴引入烷基链对分子进行修饰，可诱导形成一维微米纤维，该结果通过荧光显微镜与扫描电子显微镜（SEM）得到了验证。