Synthesis and photophysical properties of helical carbon nanohoops with twisted acene panels

Abstract

Two helical carbon nanohoops, [7]CPPNap_1,5 and [7]CPPAn_1,5, which can be viewed as finite molecular models of chiral [9,7] or [10,6]CNTs with different chiral angles were designed and synthesized. The structures were confirmed by HR-MS, NMR, and X-ray diffraction analysis ([7]CPPNap_1,5 only). Changing the connection positions from 2,6-linkage to 1,5-linkage with the acene in the cyclic structure makes the racemization process easier through fast rotation of the acene around the C–C single bonds, as disclosed by transition-state calculations. The ring strains were calculated and further visualized to provide the strain distributions. Photophysical investigations revealed that acene-inserted carbon nanohoops showed multiple and widened absorption profiles with non-forbidden S₁ absorptions.