We synthesized a series of carbon nanohoops, [n]CPP-BODIPY (n = 6, 7, and 9), by embedding boron dipyrromethene (BODIPY) dye into cycloparaphenylene scaffolds. Due to the unique size effect and intramolecular charge transfer (ICT) character within carbon nanohoops, these compounds exhibit a distinct dark green color in the solid state, as well as in solutions.

Abstract

Molecules that absorb red or near-infrared (NIR) light have been widely utilized in various fields with most reported NIR-absorbing materials focusing on planar conjugated molecules and polymers. However, the potential of curved carbon nanohoops as NIR absorbers has yet to be investigated. In this present study, for the first time, we synthesize a series of novel carbon nanohoops [n]CPP-BODIPY (n = 6, 7, and 9) by embedding boron dipyrromethene (BODIPY) dye into cycloparaphenylene scaffolds. These compounds exhibit an exclusive dark green color in the solid state. Remarkably, the absorption maxima of [n]CPP-BODIPY (n = 6, 7, and 9) exhibited a redshift over 140–170 nm compared to the BODIPY monomer and even > 300 nm compared to their corresponding CPP nanohoops, extending absorption features into the first NIR window. This establishes them as a novel class of carbon nanohoops with the most significant redshifted absorption to date. The successful application of this approach introduces a novel concept for synthesizing NIR absorbers based on CPP structures.