Supramolecular Order of 2,5-Bis(dodecanoxy)phenyleneethynylene–Butadiyne Oligomers in the Solid State
2015
Vergara, Edgar | Arias, Eduardo | Moggio, Ivana | Gallardo-Vega, Carlos | Ziolo, Ronald F. | Jiménez-Barrera, Rosa M. | Navarro, Damaso | Rodriguez, Oli | Fernández Ramírez, Salvador | Herrera, Manolo
The supramolecular order of a 2,5-bis(dodecanoxy)phenyleneethynylene–butadiyne series of rod-like 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 π–π 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.
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