Poly((2,5-dialkoxy-p-phenylene)ethynylene-p-phenyleneethynylene)s and their model compounds

Poly((2, 5-bis(n-hexyloxy)-p-phenylene)ethynylene-p-phenyleneethynyl) (1a), poly((2, 5-bis (n-dodecyloxy)-p-phenylene)ethynylene-p-phenyleneethynylene) (1b), 1, 4-diphenylethynylene-2, 5-bis(n-hexyloxy)benzene (2a), and 1, 4-diphenylethynylene-2, 5-bis(n-dodecyloxy)benzene (2b) have been prepared by the Heck reaction. The X-ray crystal structures of 2a and 2b show that the overlap between aryl rings in neighboring molecules is small for 2a but large for 2b. 2a and 2b have similar electronic absorption spectra, and emission spectra in dilute solution, but the thin film emission of 2b is red shifted about 40 nm, perhaps due to excimer cluster formation or aggregation. Likewise, polymers 1a and 1b have similar absorption spectra and emission spectra in solution, but in the solid state the emission of Ib is significantly red shifted, also consistent with aggregation.