Molecular modelling of hyperbranched polyacetylene

Ab initio and density functional theory calculations carried out on linear and dendritic polyacetylenic (PA) oligomers of different size showed that a cetylenic dendrimers are less stable than trans-PA oligomers and that the i nstability increases with molecular weight reflecting the strain in crowded hyperbranched structures. However, the energy difference between linear an d dendritic structure is rather small and tends to a limit with molecular w eight. Twisting of the double bonds decreases the conjugation in hyperbranc hed PA compared to linear trans-PA. However, the conjugation though less ef fective than in trans-PA is extended up to the 4(th) or 5(th) generation of dendrimers. It was shown that bromine end groups strongly affect the elect ronic properties of acetylenic dendrimers decreasing even more the conjugat ion due to the: sterical hindrances, however, highly polarizable bromine at oms reduced significantly the adiabatic potentials of ionization to be very close to that for trans-PA oligomers.