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An optically active poly(phenylacetylene), poly{2-(R)-methyl-2-[4 0 -(tetradecyloxy)biphenyl-4-yloxy]propyl 4-ethynylbenzoate} (P1) is synthesized in a high yield with a high molecular weight (1.3 � 10 6 g/ mol) by [Rh(nbd)Cl]2 catalyst. The chemical structure of the polymer is characterized by IR and NMR spectroscopies with satisfactory analysis data. The polymer is soluble in many common organic solvents. It shows circular dichroism (CD) band in the absorption region of the polyacetylene backbone, indicating that P1 is chiroptical owing to the formation of helical conformation with an excess screw sense. Combining the results of CD and light scattering experiments, we find that addition of poor solvent can induce the neighboring helical segments within a single polymer strand to become closer, resulting in exciton coupling prior to polymer precipitation. The exciton coupling can be kept in the solid state after solvent evaporation.

The phase structures and transition behaviors of a series of side-chain liquid crystalline (LC) polymethacrylates based on p-methoxyazobenzene (PMnAzs, n ¼ 6, 8, 10, 12) were studied using differential scanning calorimetry, one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction, and Fourier transform infrared spectroscopic experiments. The LC phase transition of PMnAz follows the sequence of smectic A (SmA)4 nematic (N)4 isotropic (I). For PM10Az and PM12Az, the transition of SmA-to-N is not complete upon heating. In the low-temperature SmA phase, the polymers adopt a fully interdigitated side-chain packing with the smectic layer period almost identical to the side-chain length. For all the four samples, the first-order diffraction of the SmA structure only renders when the temperature approaches the transition of SmA 4 N, with the intensity much lower than that of the second-order diffraction. The absence of the first-order diffraction at low temperatures is ascribed to the possible matching of the electron densities between the center portion of the side-chain sublayer and the main-chain sublayer of the SmA structure. Since only the mesogens from the same main-chain sublayer can stack parallel together, the distribution of the azobenzene domains may cause some sort of density undulation within the smectic layer. Among the samples, PM6Az presents the strongest undulation with some additional orders. We also examined the annealing effect on the H-aggregation of PMnAzs. It is found that isothermal annealing at a temperature slightly higher than the T g of PM8Az and PM10Az can significantly enhance