Synthesis of novel optically active poly(thiophenyleneethynylenephenylene)s. Effects of chirality competition and cooperation at the side chains on higher order structures

Novel poly(thiophenyleneethynylenephenylene)s having optically inactive/active amide groups were synthesized by the Sonoghashira-Hagihara coupling polymerization of 3-substituted 2,5-dibromothiophene 1 with 1-substituted 3,5-diethynylbenzenes 2N, 2R, 2S derived from glycine and d-/ʟ-alanines. Poly(1–2S) exhibited an intense Cotton effect based on negative exciton chirality at 405 and 366 nm. On the other hand, poly(1–2N) exhibited a Cotton effect similar to that of poly(1–2S) but weaker, and poly(1–2R) exhibited a weak Cotton effect based on positive exciton chirality. The chiral secondary structures of the polymers were dependent on chirality cooperation and chirality competition of the side chains. The trend of the circular dichroism (CD) signs and intensities of the polymers can be explained by the concepts of “chiral cooperation” and “chiral competition” between the optically active thiophene unit and optically inactive/active phenylene unit. These polymers formed aggregate structures with increasing MeOH content of CHCl3/MeOH mixed solvents, with accompanying decrease of the UV–vis absorptions and photoluminescence (PL) intensities. [Display omitted]