Spiral Graphene Nanoribbons with Azulene Defects as Potential Nonlinear Optical Materials

Inducing new nonlinear optical (NLO) properties while keeping the thermal stability of carbon-based nanomaterials paves a new path for the application of carbon nanomaterials in optoelectronics. In the present work, azulene units are introduced to spiral carbon nanoribbons to enhance the polarity of the charge distribution in spiral carbon nanoribbons, significantly enhancing the first hyperpolarizabilities of those nanoribbons and making the nanoribbons potential nonlinear optical materials. For example, the static first hyperpolarizability of azulene-defected spiral graphene nanoribbon with eight units (ADSGN8) is 2499.0 × 10–30 esu, whereas that of azulene spiral graphene nanoribbon (SGN8) is only 12.0 × 10–30 esu. The two-dimensional second-order NLO spectra predicted by the sum-over-states model reveal the strong second-order NLO responses of the nanomaterials under external fields, particularly within the visible region of approximately 600.0 nm. The origin of the first hyperpolarizability of azulene-defected spiral carbon nanoribbons is scrutinized and further improvement on the NLO responses of those systems is proposed.