[n]Helicenes with Red to Near-Infrared (NIR) Emissions and Circularly Polarized Luminescence

The access to various [n]helicenes holds significant values in synthetic chemistry and materials science due to the unique helically chiral structures and potential applications in chiroptoelectronic materials. Particularly, one of the challenges and current interests as well in this area is to construct new chiral systems that can promise intriguing light-emitting properties and long-wavelength circularly polarized luminescence (CPL). In general, the luminescence and CPL spectra have proved to be effectively tuned into the far-red and near-infrared (NIR) regions with reasonably high emission quantum efficiency via extension of π-conjugation or fused-ring expansion. As the other proof-of-concept, heteroatom doping of main-group elements (e.g., O, S, N, B) has also served to enable the precise modulation of molecular electronic structures with reduced HOMO-LUMO energy gaps, leading to the improved performance of NIR CPL. Our minireview offers an overview of rapid progress recently achieved in these emerging chiroptical materials together with extensive discussions on the design strategy and chiroptics both for carbo[n]helicenes and for hetero[n]helicenes, which may provide some new insights into the further pursuit of high-performance NIR-active chiral luminescent materials.