New Alternative Donor−Acceptor Arranged Poly(Aryleneethynylene)s and Their Related Compounds Composed of Five-Membered Electron-Accepting 1,3,4-Thiadiazole, 1,2,4-Triazole, or 3,4-Dinitrothiophene Units:  Synthesis, Packing Structure, and Optical Properties

Abstract

A series of new poly(aryleneethynylene)-type π-conjugated copolymers, which consist of an electron-accepting 1,3,4-thiadiazole, 4-alkyl-1,2,4-triazole, or 3,4-dinitrothiophene unit and an electron-donating 1,4-didodecyloxybenzene or N-dodecylpyrrole unit, were prepared in 81−93% yields by palladium-catalyzed polycondensation. Their related model compounds (PhC≡C−Ar−C≡CPh; Ar = the electron-accepting unit) were also synthesized. GPC traces of the polymers gave number average molecular weights (Mn's) of 6900−29 700. The polymers formed a molecular assembly and a birefringent phase as revealed by powder X-ray diffraction (XRD) analysis and polarized light optical microscopy (POM). They formed an aligned structure on a platinum plate. The UV−vis peaks of the polymers appeared in the range of 385−522 nm in solutions, and the peak was shifted by 10−44 nm to a longer wavelength in films, according to intermolecular electronic interaction. The density functional theory (DFT) calculations supported the presence of strong intermolecular interaction between the polymer molecules. The polymers composed of a 1,3,4-thiadiazole or a 1,2,4-triazole unit exhibited photoluminescence with quantum yields of about 50% in chloroform. The polymers were electrochemically active and showed the reduction peak in a range of −1.1 through −2.2 V vs Ag+/Ag