Configuration and conformation of poly(3-carbazolylacetylene) including cis and trans radicals revealed by ESR spectroscopy

π-Conjugated cis and trans radicals of poly(N-isobutyl-3-carbazolylacetylene), P(iBCzA), were stereospecifically prepared using the [Rh(norbornadiene)Cl]2-triethylamine catalyst in toluene as the polymerization solvent at room temperature, and their geometric structures were determined using the electron spin resonance (ESR) method. The deuterated analogue, P(iBCzA-d1), with vinyl protons replaced with deuterium, D–C, was used to corroborate the structures together with the simulation of the observed ESR spectra and the calculation of the spin densities of the two radicals. The cis and trans radicals were generated at 1 : 1 ratio with spin densities delocalized on the main chain rather than the side-chain, unlike other substituted polyacetylenes, which have relatively small side-chains. This finding indicates that the large and planar carbazole moieties of the two radicals were perpendicular to the π-conjugated main-chain and that fairly stiff π-conjugated main chains were generated.