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 B n N 3– n -CPLY 3 ( 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 (C 60 ), resulting in the formation of supramolecular complexes termed B n N 3– n -CPLY 3 @C 60 ( 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 B n N 3– n -CPLY 3 @C 60 ( n = 0, 1, 2) are higher compared to that of B 3 -CPLY 3 @C 60, 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 B n N 3– n -CPLY 3 @C 60 ( n = 0, 1, 2) are attributed to the host–guest interaction between B n N 3– n -CPLY 3 and C 60 . Furthermore, CT spectroscopy, main electron transition, and CT properties are studied to gain insights into the optical properties of B n N 3– n -CPLY 3 @C 60 . 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 B n N 3– n -CPLY 3 @C 60 complexes are important materials for optoelectronic applications.