Origin of the color of π‐conjugated columnar polymers: Poly(p‐n‐octylthiophenyl)acetylene prepared using a [Rh(norbornadiene)Cl]₂ catalyst

Abstract

Highly stereospecific polymerization of a novel sulfur containing aromatic acetylenes, that is, (p-n-octylthiophenyl)acetylene (pOctSPA), was successfully performed using the Rh complex, [Rh(norbornadiene)Cl] 2 -TEA, catalyst in the presence of various solvents under mild conditions. The resulting polymers were characterized in detail by 1 H NMR, ESR, laser Raman, diffuse reflective UV-Vis (DRUV-Vis), and wide angle X-ray diffraction methods. The data showed that the resulting polymers bear cis-transoid form, which can induce the cis-to-trans isomerization when the cis polymers are subjected to pressure at room temperature under vacuum, breaking rotationally the cis C¼ ¼C bonds in the main-chain giving two kinds of -radicals, the so-called cis radical and trans radical as the origin of a polymer magnet like a novel spin glass material. Further, the resulting cis poly(acetylene)s were found to have a helical main-chain, which is packed in pseudohexagonal crystal called -conjugated columnar or nano -conjugated columnar as a novel color controllable material.

SEC/DAD and1H NMR Study of Molecular Weight and Configurational Stability of Poly(2,4-difluorophenylacetylene) and Polyphenylacetylene Prepared with Rh Catalyst

“…Let us now assume the cis-to-trans isomerization proceeding (at least partly) via the rotational scission of the mainchain double bonds that leads to the increase of the content of unpaired electrons on the isomerized polymer chains [69][70][71][72][73]86] as it is known from the pressure-induced cis-to-trans isomerization of polyarylacetylenes. Assuming that the degradation of PdFPhA and PPhA is initiated by reaction of O 2 with the unpaired electrons on polymer chains, the isomerized cis/trans macromolecules should be more prone to the degradation compared to the high-cis microstructurally unperturbed macromolecules with a lower unpaired electrons content.…”

“…Isomerization proceeding by itself should lead to formation of more conjugated cis/trans main-chain sequences that should be manifested by a red shift in the visible spectrum. [69][70][71][72][73] If both processes proceed simultaneously and if the increase in conjugation due to cisto-trans isomerization overwhelms the declension in conjugation due to degradation the red shift in the visible spectrum may be expected.…”

“…The subject of particular interest in this field has been the pressureinduced cis-to-trans isomerization of these polymers in the solid state. [69][70][71][72][73][74] This phenomenon is manifested by (i) red shift in the UV-Vis spectra due to the increase in the effective conjugation length and (ii) a significant increase in the concentration of mobile unpaired electrons (solitons) on the polymer chains. [69] Since this process usually leads to the decrease in polymer solubility no reliable data is available on the eventual changes in MW accompanying cis-to-trans isomerization.…”

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

“…It is also noteworthy, therefore, that even in the ESR spectrum of other aromatic polyacetylenes having a hetero atom other than halogen, two peaks may be separately observed as those of cis and trans geometrical isomers when the pristine cis polymer was prepared with the Rh complex catalyst under quite mild polymerization conditions followed by compression as reported before. [27,28] As we have already shown above when the PpIPA was compressed we can have two ESR peaks which are assigned to the cis and trans radicals. Therefore, if two points using the g values, 2.0067 and 2.0024 due to cis and trans radicals are depicted in the Figure 5 and these points were connected with the vertical line at g % 2.0024 we will be able to deduce the cis or trans geometries of the compressed polymer.…”

Molecular weight and configurational stability of poly(phenylacetylene) prepared with Rh catalyst

“…The subject of great interest in this field has been the pressure-or temperature-induced cis-to-trans isomerisation of these polymers in the solid state [74e79]. This phenomenon is manifested by (i) red shift in the vis spectra due to the increase in the effective conjugation length and (ii) significant increase in the concentration of mobile unpaired electrons (solitons) on the polymer chains (up to 20-fold) [74]. Since this process usually leads to the decrease in polymer solubility no reliable data is available on the eventual changes in MW accompanying cis-to-trans isomerisation.…”