Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

Abstract

Angle-selection experiments of a spin soliton in randomly oriented ladder polydiacetylene were carried out by pulsed electron paramagnetie resonance (EPR) at W-band. EPR measurement using 94 GHz mierowaves increased the difference in the resonance field due to g anisotropy of the spin soliton to allow the orientation dependence of transient nutation, electron nuclear double resonance (ENDOR) and spin relaxations to be investigated. The shape of the g anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the [3 protons (HI3) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence in the Tt and T z processes was found in terms of isotropy of the H~-hyperfine interaction.

Conjugated Polymers and Aromaticity

“…When s = 2, the system can be called a diacetylene coupled polydiacetylene ladder (DACPDAL, 40 ), which is the only one that has been obtained experimentally so far . This system has also been extensively studied by a series of spectroscopic techniques. − The properties of the ladder can be further tuned by substitutions at the side group R. Generally, one would expect that the couplings through the oligoyne units add extra conjugation pathways for these ladder polymers, relative to the parent pair of PDAs . This coupling would be qualitatively different from the case of polyacene, as discussed before, because in that case the frontier orbitals are localized on the edge carbons.…”