Constructing a mixed π-conjugated bridge to effectively enhance the nonlinear optical response in the Möbius cyclacene-based systems

Abstract

Using density functional theory computations, employing the concept of a mixed π-conjugated bridge can effectively improve the first hyperpolarizability (β₀) of Möbius cyclacene (MC)-based systems with a D–π–A framework. This mixed π-conjugated bridge is constructed by applying a –(CHCH)_x–NH₂ or –(CHCH)_x–NO₂ chain to modify [8]MC, which can lead to a considerable β₀ value (e.g. [8]MC–(CHCH)₁₂–NO₂ (9.87 × 10⁵ au) with only a certain chain length), much larger than the sole [8]MC (261 au) and the corresponding NH₂/NO₂-modified polyethylene chain with the same π-conjugated length. It is revealed that the substituent sites and the chain length can play a crucial role in improving β₀ values of these MC–chain systems, where the β₀ value can monotonically increase with increasing –(CHCH)_x– length, and the substituent electron-withdrawing –(CHCH)_x–NO₂ chain is superior to the parallel electron-donating –(CHCH)_x–NH₂. These appealing findings can provide valuable insights into the design of novel NLO materials based on MC.