Rigid Rod Conjugated Polymers for Nonlinear Optics. 3. Intramolecular H Bond Effects on Poly(phenyleneethynylene) Chains

Abstract

This paper describes the synthesis and the X-ray and the optical characterization of conjugated soluble polymers in which the planarity of the backbone has been improved by intramolecular H bonds. The solubility of the polymers was enhanced by increasing the number of alkyl chains on the aryl group. The electron density on the phenyl ring was also modified by the amino and ester groups, introducing electron-donor or electron-acceptor groups, which also increase the polarizability. The polymers have been synthesized by polycondensation using a palladium-catalyzed coupling reaction, between a bromoaryl and an ethynylaryl unit, with HBr elimination. This method allows the insertion of a triple bond between two phenyl groups. It was initially used in our laboratory to obtain oligomers or high molecular weight polymers, having important nonlinear susceptibilities. The new polymers have been characterized by UV−visible and Raman spectroscopies, as well as nonlinear optical measurements of the third-order susceptibilities (χ(3)). These measurements allowed us to show the influence of the H bonds between the aryl groups on the absorption wavelength. In addition, the nonlinear optical measurements show that the χ(3) value of the pPY (6.8 × 10-10 esu) is close to the highest values obtained in acetylenic polymers such as polydiacetylenes.

Investigation on the synthesis and reaction of new aniline derivatives in Pd-catalyzed cross-coupling

“…The assignment of the ethynyl-H to the 5-position was determined by NOESY. These experimental results are in agreement with those of Moroni et al They isolated the 2,5-diethynyl-4-(didodecylamino)-N -dodecylaniline monomer only in a low yield, too [13]. We assume that the steric hindrance together with the known negative effect that electron-donating groups have in the Pd-catalyzed cross-coupling causes these phenomena.…”

“…Kieselgel 60 by Merck was used for column chromatography. 13 C-NMR spectra were recorded on a Bruker DRX 400 and a Bruker AC 250. CDCl 3 , DMSO-D 6 , and acetone-D 6 were used as solvents.…”

Transport and Electro‐Optical Properties in Polymeric Self‐Assembled Systems

“…Comb-shaped regioregular poly(4-alkylquinoline-2,6-diyl)s show lamellar structures and p-stacking and emit yellow light at 542-557 nm [313]. Finally, it is pointed that the planarity can be controlled by supramolecules interactions [314,315].…”

New oligomers with alternating phenylene ethynylene pyridinylene structure

“…In order to increase the solubility of these rigid, linear polymers alkyl or alkoxy groups have been introduced. To our knowledge, only monoalkylamino substituents were used [8,9]. This is surprising, since Scheme 1.…”