Theoretical Insights into the Formation and Optical Properties of C₆₀ ^out and C₆₀ ⁱⁿ Supramolecular Isomerism

This work investigates how the spatial arrangement of host-guest complexes influences their nonlinear optical (NLO) responses, focusing on the isomerism of cycloparaphenylene (CPP) and fullerene (C₆₀) systems. Using density functional theory (DFT), we compare the geometry and NLO properties of C₆₀ located inside (C₆₀ ⁱⁿ) and outside (C₆₀ ^out) of boron- and nitrogen-doped nanorings (BCP and NCP). C₆₀ ⁱⁿ form is more stable due to strong dispersion interactions, while C₆₀ ^out isomers yield significantly higher first hyperpolarizabilities (β_tot). This performance difference arises from the distinct charge-transfer (CT) pathways, where C₆₀ ^out@BCP exhibits large intramolecular CT within the host, whereas C₆₀ ^out@NCP induces a new intermolecular CT process from the host to the guest. Furthermore, C₆₀ ^out form exhibits high sensitivity to external electric fields, allowing for effective modulation of second-order NLO responses. These findings propose that C₆₀ ^out form is distinct from the traditional C₆₀@[10]CPP, offering new idea for designing high-efficiency organic optoelectronic materials.