Semiconducting and conducting transition of covalent-organic polymers induced by defects.

The chemical doping method is often adopted to obtain metal-free conducting materials. To date, it is still a great challenge to controllably prepare metal-free semiconducting and conducting materials by tuning the inherent structure of a material. In this work, a class of novel one-dimensional (1D) covalent-organic polymer (COP) has been designed, whose cross-sections are triangular, tetragonal, pentagonal and hexagonal, and their electronic properties are explored. The tetragonal 1D COP exhibits unique phenomena in electronic properties, i.e. the tetragonal COPs with mono- or trilayer defects (odd defects) show semiconducting properties, while they become conductors for the two cases of non- or bilayer defects (even defects). This observation indicates that they comply with the characteristics of semiconducting and conducting switches induced by the odd-even defects. Therefore, we infer that for the tetragonal configuration, the odd-even defects could potentially manipulate the electrical behavior of the COP material. The discovery provides a new direction for the targeted synthesis of semiconducting and conducting materials by tuning the inherent structure of materials, which is entirely different from the chemical doping method yielding metal-free conducting materials.