Local electronic excitation mechanism for nanofabrication of polydiacetylene molecular wire

Mechanism of electron-excitation-induced polymerization from diacetylene monomer to polydiactylene was studied theoretically. The single electron configuration interaction (SE-CI) method based on abinitio Hartree-Fock crystal orbital theory was used for the calculation. Potential energy curves of electronically excited singlet and triplet states along a hypothetical reaction coordinate were calculated. The lowest triplet state of miss-aligned diacetylene monomer was found to be metastable, which agrees with experiments. The local electronic excitation mechanism found in this polymerization reaction was discussed in the context of the polymerization initiated by scanning tunneling microscope (STM).