Halogen bond-modulated solid-state reordering and symmetry breaking of azahelicenes
Juncong Liang, Fuwei Gan, Guoli Zhang, Chengshuo Shen, Huibin Qiu
Abstract
Spontaneous symmetry breaking predominately occurs during the aggregation of discrete molecules in solution. Herein, we report a unique solid-state symmetry breaking process of dynamically chiral aza[4]helicenes that emerged in vacuum-driven transformation of halogen bond-woven crystals. Due to the weak feature of the halogen bonding, the halides in the cocrystals can be completely removed under vacuum at an elevated temperature. Interestingly, the aza[4]helicene molecules released from the halogen bond network solely adopt one chiral conformation upon reordering and symmetry breaking instantly occurs in a solid state. The Cotton effects gradually increase with the extension of vacuum–heating treatment, indicating a unidirectional transformation of the chiral conformations and an amplification of symmetry breaking during the solid-state reorganization. Moreover, the use of aza[6]helicene as a chiral inducer further enables a precise manipulation for the absolute configuration of the solid-state symmetry breaking, paving a distinctive route to chiral organic materials from achiral/racemic precursors. Spontaneous symmetry breaking predominately occurs during the aggregation of discrete molecules in solution. Herein, the authors report a solid-state symmetry breaking process of dynamically chiral aza[4]helicenes that emerges in vacuum-driven transformation of halogen bond-woven crystals.