Naphthalene Diimide-Embedded Donor–Acceptor Carbon Nanohoops: Photophysical, Photoconductive, and Charge Transport Properties

Designing the architecture of donor-acceptor (D-A) pairs is an effective strategy to tailor the electronic structure of conjugated macrocycles for optoelectronic devices. Herein, we present the synthesis of three D-A nanohoops <b>NDI-[<i>n</i>]CPP</b> (<i>n</i> = 7, 8, 9) containing a naphthalene diimide (NDI) unit as an acceptor and [<i>n</i>]cycloparaphenylenes ([<i>n</i>]CPPs) moieties as donors. The D-A characteristics of <b>NDI-[7-9]CPPs</b> were substantiated through absorption and fluorescence spectroscopic studies, electrochemical investigations, and computational analysis. The device investigations demonstrated that the D-A nanohoops <b>NDI-[7-9]CPPs</b> can serve as the photoconductive layer and demonstrate a significant generation of photocurrent with a fast response upon exposure to light. The magnitude of photocurrent shows high dependence on the size of their rings, with an increasing tendency as the ring size decreases. The generation of photocurrent in free acceptor-based CPP has rarely been reported in the previous literature. Significantly, the C₆₀ complexes of <b>NDI-[7-9]CPPs</b> exhibited a marked enhancement in photocurrent under identical conditions; in particular, the photocurrent of <b>C</b>_<b>60</b><b>⊂NDI-[7]CPP</b> is ca. 3.5 times greater than that of <b>NDI-[7]CPP</b> alone. Furthermore, the potential applications of <b>NDI-[7-9]CPPs</b> in electron- and hole-transport devices have also been explored, revealing the clear evidence of their bipolar behavior as an active charge transport layer.