An ab initio study of structural stability of poly(phenylacetylene) dimers and trimers

The energies of various stable isomers of poly(phenylacetylene) dimers and trimers were optimized by ab initio methods. The calculations were performed by using the 3-21G and 6-31G* basis sets. The stability of the dimers was predicted to increase in the order: dimer 2 > dimer 3 > dimer 1. From the calculated energies, dimer 2 (trans) is predicted to be about 2 kcal mol^-1 lower in energy than dimer 3 (cis). The cis - trans (structures 1 and 3), and trans - trans (structures 5 and 6) trimers, were predicted to have the most stable isomers. Only trimer 3 can be formed from dimer 2. Thus, the polymer formation is most likely to occur based on this trimer with a tail - head - tail - head addition.