Polycyclic aromatic hydrocarbons (PAHs) refer to compounds in which two or more benzene rings are linked together, mainly fused-ring aromatic hydrocarbons. Common parent compounds include naphthacene, pentacene, and pyrene. All carbon-based compounds such as pyrene, indece, fluorene, azulene, and rubicene, as well as complex fused-ring molecules doped with heteroatoms such as S, Se, and N. Such molecules usually have excellent and unique optoelectronic properties, and the study of the structure-activity relationship of PAHs materials is crucial for improving semiconductor properties, so it is a research hotspot in the field of organic semiconductor materials. However, even PAHs with simple structures still have the problem of lengthy synthetic routes, and in addition, they involve high energy consumption and low-yield stuck-neck reaction steps. The overall yield is generally low, and the material cost remains high.

        The team of Prof. Hui Huang/Associate Prof. Qinqin Shi from the University of Chinese Academy of Sciences used polysubstituted alkenes as important synthetic intermediates and combined multiple dehydrogenation strategies to synthesize three types of heteroatom-doped PAHs with a two-step total yield of 40 -70%, a significant improvement compared to traditional synthesis methods.

        For the synthesis of polysubstituted alkenes, the authors used acylhydrazone nucleophiles, which are safer to handle than metal nucleophiles. Through the modulation of substituents, the authors achieved efficient introduction of alkyl and aryl chains. In addition, the introduction of asymmetric groups also lays the foundation for the synthesis of complex macromolecules. Finally, the authors synthesized three different types of fused-ring PAHs, rubicene, ABT and IDT, respectively, by Scholl oxidation off ring, optical off ring and Fick off ring.

       The optoelectronic properties of heteroatom-doped rubicene are rarely reported. X-ray single crystal diffraction results show that the doping of heteroatoms is very important for regulating molecular planarity. First, the twist angle of heteroatom-doped rubicene molecules is generally lower than 20 degrees, which is smaller than that of all carbon-based rubicene molecules. Second, the degree of planarity can be adjusted by doping control of heteroatoms. For example, the twist angle of thiophenes is generally less than 10 degrees, the molecular π-π stacking is good, and the intermolecular distance is short; while the selenophenol-based rubicene almost does not observe π-π stacking. This difference leads to a much higher hole mobility of thiophene rubicene than selenophene rubicene in single crystal field effect transistors. At the same time, the heavy atom effect of selenium and the twisted structure of selenophene rubicene will reduce the energy difference between the singlet state and triplet state of the molecule, and promote intersystem crossing. Through the study of transient absorption on the lifetime of various exciton excited states, it is found that the yield of the triplet state of selenium phenophene rubicene can reach 100%, which is relatively rare in organic semiconductor materials, and has potential application prospects in luminescence and cancer treatment. .

        This achievement was recently published in Angewandte Chemie International Edition. The first author of the article is Associate Professor Shi Qinqin of the University of Chinese Academy of Sciences, and the corresponding authors are Professor Huang Hui and Associate Professor Shi Qinqin of the University of Chinese Academy of Sciences and Simon B. Blakey of Emory University.