화학공학소재연구정보센터
Langmuir, Vol.31, No.24, 6909-6916, 2015
Supramolecular Order of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiyne Oligomers in the Solid State
The supramolecular order of a 2,5-bis(dodecanoxy)phenyleneethynylene-butadiyne series of rodlike oligomers with 2, 4, 6, and 8 phenyleneethynylene moieties was studied in the solid state by differential scanning calorimetry (DSC), temperature-dependent small- and wide-angle X-ray scattering (SWAXS), selected area electron diffraction (SAED), polarized optical microscopy (POM), high-resolution transmission microscopy (HRTEM), and scanning tunneling microscopy (STM). It was found that all of the oligomers self-assemble in blocks of molecules that resemble bricks that are randomly oriented. These oligomers are described as sanidic liquid crystals as a term to classify their mesomorphic behavior because of their brick or board-like structure. The strong pi-pi interaction that governs the package of conjugated backbones was evidenced by the reiterative distances of 0.36 +/- 0.017 nm found by SWAXS and 0.32 +/- 0.017 nm found by HRTEM. A STM study of a cast film of the tetramer deposited on highly oriented pyrolitic graphite (HOPG) allowed for the visualization and determination of the conjugated backbone length of 2.48 nm and a phenyl-phenyl distance of 0.34 nm, suggesting that the molecules are stacked in lamellae perpendicularly aligned to the substrate.