New substituted polyacetylenes with phenyleneethynylene side groups [-(C6H4-C C)(n)-(SiPr3)-Pr-i; n=1, 2]: Synthesis, characterization, spectroscopic, and photoelectric properties

The selective, terminal triple bond polymerization of HC=C-C6H4-C=C-(SiPr3) -Pr-i (1) and HC=C-C6H4-C=C-C6H4-C=C-(SiPr3)-Pr-i (2) yields soluble, high- MW polyacetylenes P1 and P2 with phenyleneethynylene-type pendant chains. T he [Rh(cod)(OCH3)](2)- and MoCl5-based catalysts show 100% polymerization s electivity to terminal triple bonds and give high-cis (NMR: Rh, 94% cis; Mo , 70% cis) polymers having a medium extent of pi-conjugation. WOCl4-based c atalysts reacting in benzene marginally also insert internal triple bonds a nd give low-cis polymers (<10% cis) having a high extent of conjugation. Ad dition of 1,4-dioxane to the WOCl4-based catalyst considerably reduces or e ven eliminates the internal triple bond insertion and increases the polymer molecular weight, cis-unit content (approximate to 35% cis) and extent of pi-conjugation. The pi-pi* band of P1 pendant groups is closely correlated with the polymer microstructure: the cis-unit content in P1 can be reliably ascertained from the A(292)/A(268) UV-absorbance ratio. Raman bands of the main-chain v(C=C) mode exhibit both frequency and intensity dispersion wit h extent of conjugation. On the other hand, only intensity dispersion is co nclusively observed for the v(Ph-C-chain) band at 1341 cm(-1) that, upon co rrection to the dispersion effect, is in a good correlation with the cis-un it content obtained from NMR spectra. Xerographic and transient photoconduc tivity measurements have shown that the photogeneration in these polymers p roceeds through the side group excited states, and the charge carrier's (ho les) transport is controlled by hopping between the main chain conjugated s equences.