Structure-property relationships for photoconduction in substituted polyacetylenes

New photoconductive materials are explored from three groups of polyacetyle nes: poly(phenylacetylenes) -[HC=C(C6H5-p-R)](n)-, poly(3-thienylacetylenes ) -[HC=C(3-C4H2S-beta-R')](n)-, and poly(1-alkynes) -{HC-C[(CH2)(m)R "]}(n) -, where R = CH3 (2), CO2(CH2)(6)OCO-Biph-OC7H15 (Biph = 4,4'-biphenylyl; 3 ); R' = Si(CH3)(3) (4), Br (5); and R " = CO2(CH2)(6)OCO-Biph-OC9H19 (m = 2 ; 6), 9-carbazolyl (m = 3; 7) and OCO-Biph-OC7H15 (m = 9; 8). Photoconducti on in the polyacetylenes under illumination of visible light is investigate d using photoinduced xerographic discharge technique. In the pure (undoped) state, all the polyacetylenes except 5 show higher photosensitivity than d o poly(phenylacetylene) (R = H; 1), a well-studied photoconducting polyacet ylene, and poly(9-vinylcarbazole), the best-known photoconducting vinyl pol ymer. Among the polyacetylenes, photoconduction performance of the polymers with electron-donating and/or hole-transporting moieties is superior to th ose with electron-accepting ones. The liquid crystalline polymer 6 exhibits very high photosensitivity, probably due to the formation of crystalline a ggregates of its mesogenic pendants induced by the thermal treatment in the photoreceptor preparation process. C-60 acts as a photoconductivity enhanc er when doped tal amorphous 3, but functions as a crystallinity-breaking pl asticizer when doped to liquid crystalline g, leading to a large decrease i n photoconductivity. While 3 shows a low photosensitivity (2.8 x 10(-3) 1x( -1) s(-1)) to a 573 nm light in the undoped state, doping with I-2 and sens itization with crystal violet (CV) dramatically increase its photosensitivi ty (up to 41.2 x 10(-3) 1x(-1) s(-1)). The CV-sensitized 4 exhibits high ph otoconductivity in the near-infrared spectral region, which may find techno logical applications in the digital photoimaging systems.