A phenylacetylene bearing an n-butylsulfoxide group, i.e., p-(n-butylsulfoxide)phenylacetylene (1) was prepared in high yields using the [Rh(norbornadiene)Cl](2)-NEt3 catalyst in the presence of various solvents under mild conditions. The resulting polymer, poly [p-(n-butylsulfoxide)phenylacetylene] (poly(1)), was characterized in detail by H-1 NMR, ESR, laser Raman, and diffuse reflective UV-vis methods. The data clearly showed that cis-to-trans isomerization of the polymer can be induced when pressure is imposed to the polymer at room temperature, rotationally breaking the cis C=C bonds to generate the cis and trans radicals. Further, the spin density in the cis radical was migrated from the main-chain to the sulfoxide moiety as the side chain of the phenyl ring to magnetically interact with the first two methylene protons in the n-butyl group giving a triplet line ESR spectrum with an extremely large g value, g = 2.0081. (c) 2007 Elsevier Ltd. All rights reserved.