Incorporating a pyridinium into a cycloparaphenylene: a cationic donor-acceptor nanohoop with reversible redox properties
摘要
Py[10]CPP+ is a fully conjugated pyridinium-incorporated [10]cycloparaphenylene ([10]CPP) derivative that differs from previously reported nitrogen-doped CPPs, with its cationic nitrogen positioned at the aromatic linkage site. Single-crystal X-ray diffraction reveals that its rigid structure and dimensions are comparable to [10]CPP. Photophysical spectroscopy and DFT calculations indicate that Py[10]CPP+ adopts a donor-acceptor architecture, exhibiting a small HOMO–LUMO energy gap of 2.26 eV among cycloparaphenylene derivatives. The cationic macrocycle can be reversibly reduced to an anionic form, accompanied by a geometric change indicated by calculations, resulting in a droplet-like shape. Furthermore, the cavities of Py[10]CPP+ facilitate the formation of 1:1 host-guest complexes with C60, as confirmed by X-ray crystallography. This study not only provides a useful method for incorporating cationic nitrogen into a strained conjugated macrocyclic framework but also highlights the importance of functionalizing cycloparaphenylenes with pyridinium.