Density Functional Theory Studies of B/N-Doped Phenalenyl Nanorings with C₆₀ for Tuning Second-Order Nonlinear Optical Properties

A series of triangular nanorings, denoted BnN3–n-CPLY3 (n = 0, 1, 2, and 3), are designed by incorporating boron-/nitrogen-doped phenalenyl (B/N-PLY) units into cycloparaphenylene. These nanorings exhibit appropriate cavity size and shape complementarity to encapsulate fullerene (C60), resulting in the formation of supramolecular complexes termed BnN3–n-CPLY3@C60 (n = 0, 1, 2, 3). The geometric and electronic structures of nanorings and supramolecular complexes are investigated by density functional theory. Importantly, the self-assembly strategy effectively enhances the second-order nonlinear optical (NLO) response of the supramolecular complexes. The findings demonstrate that the first hyperpolarizabilities of BnN3–n-CPLY3@C60 (n = 0, 1, 2) are higher compared to that of B3-CPLY3@C60, which is attributed to the intra- and intermolecular charge transfer (CT) regulated by adjusting the amount of the B/N-PLY unit. By absorption spectrum analysis, the absorption peaks of BnN3–n-CPLY3@C60 (n = 0, 1, 2) are attributed to the host–guest interaction between BnN3–n-CPLY3 and C60. Furthermore, CT spectroscopy, main electron transition, and CT properties are studied to gain insights into the optical properties of BnN3–n-CPLY3@C60. This work not only emphasizes the importance of the B/N-PLY unit in supramolecular complexes to improve NLO properties but also shows that the BnN3–n-CPLY3@C60 complexes are important materials for optoelectronic applications.