The synthesis mechanism of 3-octylthien-2,5-ylenediethynylene-co-benzo[c]-1',2',5'-thiadiazo- 3,6-ylenedi(2,5-thienylene) with PdCl₂(PPh₃)₂-catalyzed is investigated by density functional theory (DFT) at the GGA/PW91/DNP level. The geometric configurations of reactants, intermediates, transition states, and products are optimized. The energy analysis calculation approves the authenticity of intermediates and transition states. Additionally, the synthesis mechanism of 3-octylthien-2,5-ylenediethynylene-co-benzo[c]- 1',2',5'-thiadiazo-3,6-ylenedi(2,5-thienylene) without PdCl₂(PPh₃)₂-catalyzed is studied employing the same functional and basis set. The computational results show that the activation barrier with PdCl₂(PPh₃)₂- catalyzed is lower than the activation barrier without PdCl₂(PPh₃)₂-catalyzed, which demonstrates that the catalyst of PdCl₂(PPh₃)₂ possesses catalytic activity. Moreover, the density functional theory and periodic slab model are used to investigate the product (P) adsorption on TiO₂(100) surface. The Mulliken charge and frontier orbital of the TiO₂(100)-P are also discussed. The results reveal that the charge of 0.692 e transfers from the P to the TiO₂(100) surface and the energy gap becomes narrow when the adsorption occurs. It is found that the above-mentioned theoretical calculations agree well with the experiment results.

Key words: 3-octylthien-2,5-ylenediethynylene-co-benzo[c]-1',2',5'-thiadiazo-3,6-ylenedi(2,5-thienylene), density functional, synthesis mechanism, electronic structure