Electronic properties of hyperbranched compounds derived by pyrrole

• Hyperbranched molecules containing pyrrole units were synthetized.
• These hyperbranched molecules show large electronic delocalization.
• Theoretical results show that para-hyperbranched polymer has an uncommon symmetry.
• The conductivity measurements indicated an energy band gap of 0.2 eV.
• Microscopy studies identify two phases where self-assembling is important.

The electronic structure of hyperbranched polymers obtained from para-diaminodiphenyldiacetylenes as AB2 type monomers by one-step polymerization is studied using DFT calculations. Five generations are modelled with optimization at each step. As the molecule grows it shows a helical shape conserving the C2 symmetry with wing like fragments covering the backbone. There is accidental degeneracy of the HOMO with the HOMO-1 and of the HOMO-2 with the HOMO-3. The LUMO is always located at the backbone and the HOMO set at the dianyline-pyrrole fragment. The HOMO–LUMO gap decreases as the molecule grows. Conductivity measurements as well as microscopy studies of para-hyperbranched polymer were carried out. Conductivity measurements as a function of temperature show semiconductor behavior. Optical microscopy reveals a macroscopic crystalline structure of this hyperbranched polymer.

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