Synthesis of zigzag-type carbocationic nanobelts

Belt[n]arenes correspond the shortest belt segments of zigzag carbon nanotubes. Their closed cyclic π-conjugated topologies and distinct size-dependent electronic configurations render them platforms for the construction of quantum materials and devices. Here, we report the synthesis of a fully conjugated carbocationic zigzag-type belt consisting of four linearly fused benzotropylium units. Belt[4]arene[4]tropylium salt was synthesized from resorcin[4]arene via a sequence featuring fjord-stitching olefin metathesis reactions, selective bromination and heterolytic C–Br bond cleavage reaction. Single crystal X-ray diffraction analysis confirms that the synthesized molecule is a rigid C4v-symmetric belt with all positively charged seven-membered rings adopting a boat conformation. Combined evidence from 1H and 13C nuclear magnetic resonance spectra, electronic absorption spectra, single crystal structural characterization and theoretical calculations demonstrates the global aromatic nature of belt[4]arene[4]tropylium.