Regulation of Circularly Polarized Emission Properties of Oxabora[6]Helicene by Inducing Dual-Emission Properties Using o -Carborane Introduction

Circularly polarized luminescence (CPL)-active materials have been attracting attention as a platform for establishing next-generation optoelectrical technologies and applications, such as a security ink for anti-counterfeiting techniques. Here we report manipulation of CPL properties of oxabora[6]helicene by introducing a boron and carbon cluster, o-carborane. In addition to the locally-excited (LE) emission band from the helicene moiety, the electron-accepting o-carborane unit can contribute to the formation of intramolecular charge-transfer (ICT)-excited states through donor‒acceptor interaction, resulting in dual-emission consisting of LE and ICT emission bands. We also found that by introducing the o-carborane cluster into the heterohelicene moiety, moderate emission efficiency can be obtained, while maintaining dual-emission properties. Oxabora[6]helicene itself showed CPL attributable to the intrinsic LE emission, while the o-carborane derivative exhibited sign-inverted CPL in the ICT emission region. According to the theoretical calculations, the inversion of CPL sign can be explained by the spatial orientational changes of transition dipole moments between o-carborane and the oxabora[6]helicene moiety in the LE and ICT states.