Photo-Assisted Bottom-Up Synthesis of Orange Phosphorus

A tubular strand of phosphorus composed of vectorially aligned pentagons has been theoretically predicted as a new allotrope of phosphorus with a polar structure, expecting potential applications. However, it has not been successfully synthesized yet due to the difficulty of creating isolated strands to avoid interchain bonding. Here, such an allotrope named "orange phosphorus" was successfully produced using a photo-assisted synthesis from an amorphous film of solution-processable Na₂P₁₆ precursors. A green laser irradiation initiated the phase transition of precursors, inducing chemical reactions like topochemical polymerization and rearrangement, creating a 1D chain of orange phosphorus. 3D electron diffraction crystallography showed that the molecular structure of orange phosphorus consists of one-dimensional polar pentagonal-tubes made up of [P8]P2[ repeat units. Orange phosphorus demonstrates excellent piezoresistivity due to its high strain-sensitive 1D chain structure, showing strain-induced Raman shifts. Its gauge factor exceeds those of 2D materials such as black phosphorus and transition metal dichalcogenides. These findings indicate that orange phosphorus has great potential for use in strain sensor applications.