Tuning optical properties of π-conjugated double nanohoops under external electric field stimuli-responsiveness

Carbon nanorings have attracted substantial interest from synthetic chemists due to their unique topological structures and distinct physical properties. An intriguing π-conjugated double-nanoring structure, denoted as [8]CPP-[10]cyclacene, was constructed via the integration of [8]cycloparaphenylene ([8]CPP) into [10]cyclacene. Using the external electric field stimuli-responsiveness of [8]CPP-[10]cyclacene, directional charge transfer can be induced, resulting in the emergence of intriguing properties. The effects of the external electric field in three specific directions were explored, vertically in the [8]CPP unit (F), vertically in the [10]cyclacene unit (F), and horizontally along the double nanorings diameter (F). Interestingly, the external electric field vertically to the [10]cyclacene unit significantly enhanced the first hyperpolarizability (β_tot) compared to that vertically to the [8]CPP unit. Notably, [8]CPP-[10]cyclacene under F exhibited significantly larger the β_tot values (1.48 × 10⁵ a.u.) than those of vertical F and F. This work opens up a wide range of nonlinear optics, making it a compelling area to explore in the field of carbon nanomaterials.