Naphthalene Diimide-Embedded\nDonor–Acceptor\nCarbon Nanohoops: Photophysical, Photoconductive, and Charge Transport\nProperties

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