Fig. 2. General structural characterization for o-PP derivatives.

a Chemical structures for o-PP-2SMe, o-PP-2CN, and o-TP-2Py, respectively. b Single crystals for o-PP-2SMe, o-PP-2CN, and o-TP-2Py, respectively. The orange dashed lines refer to the distances between sulfur atoms with exact values in orange. The blue dashed lines refer to the closest interplane distances between two biaryl groups with exact values in blue. c ¹H NMR spectrum at −5 °C of o-PP-2SMe in AA conformer (500 MHz, CD₂Cl₂) with major peaks assigned to specific protons of o-PP-2SMe in AA conformer. Asterisks: the minor signals from AB conformer. The insets include the schematic structure of o-PP-2SMe with certain letters referring to specific protons and numbers referring to the aryl rings, and two distinguishable conformers in the NMR analysis, the AA conformer corresponding to the major signals and the AB conformer corresponding to the minor signals. The two internal dihedral angles φ₂ and φ₃ are also labeled in the inset.