According to crystal structures, these materials favor twisted conformations with perfect mirror symmetry as exemplified by S/R-BNPCN-o-TBCP (Supplementary Fig. ). Close molecular packing is prevented in these materials, which is conducive to suppressing strong intermolecular interaction and alleviating emission quenching and exciton annihilation in film state. They have high decomposition temperatures of 437-446 o C, indicative of good thermal stability. A high glass-transition temperature of 225 o C observed for S-BNPCN-p-TBCP suggests its good morphological stability (Supplementary Fig. ). They also exhibit good electrochemical stability, as evidenced by reversible oxidation and reduction processes in cyclic voltammetry experiment (Supplementary Fig. ). The energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are calculated as -5.46∼-5.66 and -2.48∼-2.58 eV, respectively, from onset potentials of oxidation and reduction waves.