Synthesis and physical properties of doubly-annulated [10]cycloparaphenylene

Abstract

Abstract A doubly annulated cycloparaphenylene (CPP), in which two [N]paraphenylenes share one benzene unit by meta (m)-connection, m-,m-phenylene-[2N]CPP with N = 5 (2a), was synthesized by double annulation between a CPP precursor and 1,5-dibromo-2,4-diiodobenzene followed by reductive aromatization. The structure of 2a was confirmed by NMR, mass spectroscopy, and single crystal X-ray diffraction analysis. As 2a has a figure-eight structure, it can have a twisted Möbius topology. However, the X-ray analysis clearly reveals a non-twisted Hückel topology in a solid state. The photophysical and electrochemical properties of 2a were also clarified. The studies proved that, while 2a can also be seen as ortho (o)-,o- or para (p)-,p-connected [10]CPP, 2a has an meta (m)-,m-connected electronic structure. The theoretical calculations also support this conclusion.