Structure−Property Relationships for Photoconduction in Substituted Polyacetylenes

New photoconductive materials are explored from three groups of polyacetylenes: poly(phenylacetylenes) [HC C(C 6 H 5 - p -R)] n, poly(3-thienylacetylenes) [HC C(3-C 4 H 2 S- β -R‘)] n, and poly(1-alkynes) {HC C[(CH 2 ) m R‘ ‘]} n, where R = CH 3 ( 2 ), CO 2 (CH 2 ) 6 OCO-Biph-OC 7 H 15 (Biph = 4,4‘-biphenylyl; 3 ); R‘ = Si(CH 3 ) 3 ( 4 ), Br ( 5 ); and R‘ ‘ = CO 2 (CH 2 ) 6 OCO-Biph-OC 9 H 19 ( m = 2; 6 ), 9-carbazolyl ( m = 3; 7 ) and OCO-Biph-OC 7 H 15 ( m = 9; 8 ). Photoconduction in the polyacetylenes under illumination of visible light is investigated using photoinduced xerographic discharge technique. In the pure (undoped) state, all the polyacetylenes except 5 show higher photosensitivity than do poly(phenylacetylene) (R = H; 1 ), a well-studied photoconducting polyacetylene, and poly(9-vinylcarbazole), the best-known photoconducting vinyl polymer. Among the polyacetylenes, photoconduction performance of the polymers with electron-donating and/or hole-transporting moieties is superior to those with electron-accepting ones. The liquid crystalline polymer 6 exhibits very high photosensitivity, probably due to the formation of crystalline aggregates of its mesogenic pendants induced by the thermal treatment in the photoreceptor preparation process. C 60 acts as a photoconductivity enhancer when doped to amorphous 3, but functions as a crystallinity-breaking plasticizer when doped to liquid crystalline 6, leading to a large decrease in photoconductivity. While 3 shows a low photosensitivity (2.8 × 10 - 3 lx - 1 s - 1 ) to a 573 nm light in the undoped state, doping with I 2 and sensitization with crystal violet (CV) dramatically increase its photosensitivity (up to 41.2 × 10 - 3 lx - 1 s - 1 ). The CV-sensitized 4 exhibits high photoconductivity in the near-infrared spectral region, which may find technological applications in the digital photoimaging systems.