The trefoil is known as the simplest nontrivial molecular knot. The C₃₀ carbyne trefoil knot studied is intertwined by the sp hybridized (C≡C—)₁₅ chain, which is topologically chiral and belongs to D₃ point-group of symmetry. Density functional theory (DFT) calculations have been carried on the molecular knot at the RB3LYP/6-31G(D) levels. Based on the optimized geometry, the vibrational spectra, natural bond orbital (NBO) and orbital energy level analysis for C₃₀ carbyne trefoil knot have been calculated at the same level, and compared with the cyclo-C₃₀ carbyne molecule. The results show that the electronic structure possesses three primary attributes: C≡C nonplanar conjugated structure, inherently helical structure and highly strained crossing bonds, and the molecular orbitals are also twisted. Furthermore, the tied trefoil knot has less conjugation property and Jahn-Teller effect but higher total energy than the cyclo-C₃₀ carbyne, that is, the process of “tied” could increase the energy of molecules.

Key words: C₃₀ carbyne trefoil knot, cyclo-C₃₀ carbyne, vibrational spectrum, natural bond orbital (NBO), orbital energy level