Double Heterohelicenes Composed of Benzo[b]- and Dibenzo[b,i]phenoxazine: A Comprehensive Comparison of Their Electronic and Chiroptical Properties

Heterohelicenes are potential materials in molecular electronics and optics because of their inherent chirality and various electronic properties originating from the introduced heteroatoms. In this work, we comprehensively investigated two kinds of double NO-hetero[5]helicenes composed of 12H-benzo[b]phenoxazine (BPO) and 13H-dibenzo[b,i]phenoxazine (DBPO). Both heterohelicenes were easily synthesized by oxidative dimerization of BPO or DBPO followed by the oxidative ring fusion, and the yield of BPO-double heterohelicene was much improved compared to the previously reported DBPO-analogue. These helicenes exhibit good electron donor property reflecting the electron-rich character of their monomers and were demonstrated to work as p-type semiconductors. The enantiomers of these helicenes do not racemize at room temperature and show the largest class of dissymmetry factors for circularly polarized luminescence (CPL) (|gCPL| > 10−2) among the previously reported helicenes. Interestingly, the signs of CPL are opposite between BPO- and DBPO-double helicenes of the same helicity. The origin of the large gCPL values and the inversion of the CPL signs was addressed by analysis of the transition electronic dipole moments (TEDM) and transition magnetic dipole moments (TMDM) based on the TD-DFT calculations.