Theoretical investigation on nonlinear optical properties of carbon nanotubes with Stone–Wales defect rings

Based on (6, 0) zigzag carbon nanotubes (ZCNTs), a Stone–Wales defect ring ([5.7]3) is constructed at one end of the ZCNTs, forming a novel nanostructure [5.7]3ZCNT. The introduction of [5.7]3 breaks the centrosymmetry of the nanotube and remarkably changes electronic and magnetic properties of the nanotube. Unlike the (6, 0)ZCNT which has an open-shell singlet ground state, the [5.7]3ZCNT has a closed-shell singlet ground state with a large dipole moment, polarizability, and first hyperpolarizability. Interestingly, the [5.7]3ZCNT itself has a donor–π–acceptor framework, in which the Stone–Wales defect ring serves as an electron donor (D) while the zigzag nanotube works as an electron acceptor (A) and a conjugated bridge (π). Moreover, increasing both the tube diameter and tube length could enhance second-order nonlinear optical (NLO) responses, with the former being more effective than the latter.