<title>Liquid crystalline polyacetylenes: a new class of mesomorphic materials with novel optical and electronic properties</title>

A large number (more than 20 different kinds) of new polyacetylenes with general molecular structures of -[HC equals C(C<SUB>6</SUB>H<SUB>4</SUB>-mesogen)]<SUB>p</SUB>- [poly(arylacetylene) type] and -{HC equals C[(CH<SUB>2</SUB>)<SUB>n</SUB>-mesogen]}<SUB>p</SUB>- [poly(alkylacetylene) type] are designed and synthesized. Pendant interaction and backbone rigidity in the polymers are tuned through systematic molecular engineering endeavor, and liquid crystalline polyacetylenes (LCPAs) with novel mesomorphic, optical, and electronic properties are successfully developed. The rigid polyacetylene backbones enable ready alignments of the LCPA molecules by simple mechanical perturbations. Upon photoexcitation, the LCPAs with the poly(alkylacetylene) skeleton structure emit strong blue light clearly observable by naked eyes under normal room illumination conditions. The shape and position of the emission peaks and the color of the emitted light can be manipulated by the application of external electrical fields. The LCPAs exhibit excellent intrinsic photoconductivity in the visible spectral region in the undoped (pure) states, and doping with electron acceptor/donor further increases the photoconduction efficiency of the LCPAs.