Poly(p‐phenylene vinylene) Derivatives with Different Contents of cis‐Olefins and their Effect on the Optical Properties

Soluble poly[(2,5‐dihexyloxy‐1,4‐phenylene vinylene)‐alt‐(2,5‐diphenyl‐1,4‐phenylene vinylene)] (DPO‐PPV) with a majority of cis‐vinylenes (>87%) has been synthesized by the Wittig reaction. A series of DPO‐PPV derivatives with different contents of cis‐olefins from approximately 0.05% to 87% was successfully prepared using the photoisomerization technique. On the basis of ¹H NMR, Fourier transform IR (FTIR), ultraviolet (UV), and photoluminescence (PL) spectroscopy, as well as fluorescence quantum efficiency measurements, the effect of cis‐olefins on the optical properties of the polymer in solution and in film was systemically studied. The results indicate that with a cis‐configuration above 75%, the luminescence of DPO‐PPV is decayed due to cis‐trans isomerization with rotational motions of the double bonds; however, the luminescence is dramatically improved on increasing of the trans‐configuration.

     

Poly[(para‐halogenated)phenylacetylene]s Prepared with a [Rh(norbornadiene)Cl]2 Catalyst: Syntheses and Structure Elucidation

Summary: pXPAs were stereospecifically polymerized using [Rh(nbd)Cl]₂ as catalyst in the presence of a mixed solvent, i.e., ethanol and triethylamine, at 20 °C. The resulting PpXPAs were characterized in detail in order to predict geometrical structures concerning cis and trans configurations in the main‐chain C?C bonds using ¹H NMR, laser Raman, XRD, and ESR methods. The data showed that the PpXPAs have an extremely high content of the cis‐transoid form. Immobile unpaired electrons, ca. 1.2–3.1 × 10¹⁷ spins · g^?1, called the cis radicals, were found to be stabilized even in the pristine cis PpXPAs. The observed g values of the pristine PpXPAs could be correlated with the spin‐orbit coupling constant ζ of the halogen atom at the para position of the phenyl.

Second derivative ESR spectra of PpIPA observed (a) before and (b) after compression, and the suggested respective structures.     

Columnar Assemblies of Aliphatic Poly(acetylene ester)s Prepared with a [Rh(norbornadiene)Cl]2 Catalyst. 1H and 13C NMR,X‐Ray Diffraction and AFM Studies

Alkyl propiolates: HC≡CCOOn‐C_mH_2m+1(m = 2˜4), acetylene esters were polymerized with a [Rh(norbornadiene)Cl]₂ catalyst in methanol as the polymerization solvent to produce poly(n‐alkyl propiolate)s, PAPAs, called polyacetylene esters, in relatively high yields. The resulting PAPAs were characterized in detail using ¹H and ¹³C NMR spectroscopy, X‐ray diffraction, and atomic force microscope methods. The data showed that the resulting polymers selectively have cis‐transoid form. The cis‐transoid isomer is not amorphous but holds a pseudohexagonal structure called a columnar assembly the diameter of which agrees with those estimated by the semiempirical calculation method (AM1). The crystalline ratios of the columnar assemblies were also estimated to be ca. 60 ˜ 70%. In the case of poly(ethyl propiolate), PEPA, the crystalline size was found to approximately agree with that estimated from the AFM images of the cast film of PEPA.