OXY-P-PHENYLENE)ETHYNYLENE-P-PHENYLENEETHYNYLENE)S AND THEIR MODEL COMPOUNDS

Poly((2, xyloxy)-p-phenylene)ethynylene-p-phenyleneethynyl) (1a), poly ((2, 5-bis oxy)-p-phenylene)ethynylene-p-phenyleneethynylene) (1b), 1, 4-diphenylethynylene-2, 5-bis(n-hexyloxy)benzene (2a), and 1, 4-diphe nylethynylene-2, 5-bis(n-dodecyloxy)benzene (2b) have been prepared by the Heck reaction. The X-ray crystal structures of 2a and 2b show tha t the overlap between aryl rings in neighboring molecules is small for 2a but large for 2b. 2a and 2b have similar electronic absorption spe ctra, and emission spectra in dilute solution, but the thin film emiss ion of 2b is red shifted about 40 nm, perhaps due to excimer cluster f ormation or aggregation. Likewise, polymers 1a and 1b have similar abs orption spectra and emission spectra in solution, but in the solid sta te the emission of Ib is significantly red shifted, also consistent wi th aggregation.