Theoretical Studies on the Electronic Structure of Nano-graphenes for Applications in Nonlinear Optics

In this work, azulene is introduced into nano-graphene with coronene center to enhance the second-order nonlinear optical (NLO) properties. The sum-over-states(SOS) model based calculations demonstrate that dipolar contributions are larger than octupolar contributions to the static first hyperpolarizability() in most nano-graphenes except those with high symmetry(e.g., a C-2v nano-graphene has octupolar contributions phi(J=3) up to 59.0% of the ). Nano-graphenes containing two parallel orientating azulenes (i.e., Out-P and Out-P-s) have large dipole moments, while their ground state is triplet. Introducing B/N/BN atoms into the positions with a high spin density transfers the ground state of Out-P and Out-P-s to closed-shell singlet, and the Out-P-s-2N has a large of 1621.67x10(-30) esu. Further addition of an electron donor(NH2) at the pentagon end enhances the to 1906.22x10(-30) esu. The two-dimensional second-order NLO spectra predicted by using the SOS model find strong sum frequency generations and difference frequency generations, especially in the near-infrared and visible regions. The strategies to stabilize the electronic structure and improve the NLO properties of azulene-defect carbon nanomaterials are proposed, and those strategies to engineer nano-graphenes to be semiconducting while maintaining the pi-framework are extendable to other similar systems.

Automated summary

Azulene is introduced into nano-graphene to enhance NLO properties, with dipolar contributions being larger than octupolar contributions in most cases. Strategies to stabilize electronic structure and improve NLO properties are proposed, along with the potential for engineering nano-graphenes to be semiconducting while maintaining the pi-framework.