Morphological alignment of liquid crystalline conducting polyacetylene derivatives

We have synthesized novel liquid crystalline conducting polymers by introducing liquid crystalline group into acetylene monomer and polymerizing them with Ziegler-Natta [Fe(acac)(3) - ALEt(3)] and metathesis [MoCl5 - Ph(4)Sn] catalysts. The liquid crystalline group is composed of a phenylcyclohexyl (PCH) or biphenyl (BP) moiety as a mesogenic core, a trimethylene chain [-(CH2)(3)-] as a spacer, and an alkyl chain (-CnH2n+1, n = 2, 3, 5 similar to 8) as a terminal group. The polymers are abbreviated as PPCHn03A and PBPn03A. All polymers prepared exhibited solubility in organic solvents and smectic liquid crystallinity characterized with fan-shaped texture in polarizing optical microscopy. Phase transitions and the corresponding enthalpy changes were also evaluated by means of differential scanning calorimetry (DSC). Macroscopic alignments of the polymers were performed in the liquid crystalline phase by shear-stress or magnetic force field of 0.7 similar to 1.0 tesla, which resulted in an enhancement by two orders in electrical conductivity of iodine-doped cast films. Changes of the electronic and geometrical structures of the polymer upon the iodine-doping were elucidated by examining the effective conjugation length of a polyene chain, cis and trans thermal isomerization, and spin distribution of unpaired electrons through ultraviolet/visible (UV-Vis) and electron spin resonance (ESR) measurements.