Polymorphism of 2,5-Diphenyl-1,4-distyrylbenzene with Two cis Double Bonds: The Essential Role of Aromatic CH/π Hydrogen Bonds

Three polymorphs of 2,5-diphenyl-1,4-distyrylbenzene with two cis double bonds (cis-DPDSB) have
been prepared by altering the crystal growth conditions. The crystal data reveal that there are in total four
crystallographically independent conformations of the molecule in the three polymorphs and the backbone of cis-DPDSB largely deviates from a plane with large torsion angles in each conformation. For the three-dimensional
conformations of the molecules, there is no face-to-face stacking in all polymorphs. The aromatic CH/π hydrogen
bonds, which are identified as the main driving force for the crystal packing with interaction distances about 2.7−3.1 Å, are the origin of the variable conformations and polymorphic formations during the crystal growth processes.
Temperature-dependent IR spectra have shown that the intermolecular aromatic CH/π hydrogen bonds influence
the aromatic C−H vibrations, and the interactions become slightly decoupled when the temperature is elevated.