Helicene Covalent Organic Frameworks for Robust Light Harvesting and Efficient Energy Transfers

Abstract

Helicenes represent a class of fascinating π compounds with fused yet folded backbones. Despite their broad structural diversity, harnessing helicenes to develop well‐defined materials is still a formidable challenge. Here we report the synthesis of crystalline porous helicene materials by exploring helicenes to synthesize covalent 2D lattices and layered π frameworks. Topology‐directed polymerization of [6]helicenes and porphyrin creates 2D covalent networks with alternate helicene‐porphyrin alignment along the x and y directions at a 1.5‐nm interval and develops [6]helicene frameworks through reversed anti‐AA stack along the z direction to form segregated [6]helicene and porphyrin columnar π arrays. Notably, this π configuration enables the frameworks to be highly red luminescent with benchmark quantum yields. The [6]helicene frameworks trigger effieicnt intra‐framework singlet‐to‐singlet state energy transfer from [6]helicene to porphyrin and facilitate intermolecular triplet‐to‐triplet state energy transfer from frameworks to molecular oxygen to produce reactive oxygen species, harvesting a wide range of photons from ultraviolet to near‐infrared regions for light emitting and photo‐to‐chemical conversion. This study introduces a new family of extended frameworks, laying the groundwork for exploring well‐defined helicene materials with unprecedented structures and functions.