Nanographene-Fused Expanded Carbaporphyrin Tweezers

Abstract

A nanographene-fused expanded carbaporphyrin (<b>5</b>) and its BF₂ complex (<b>6</b>) were synthesized. Single-crystal X-ray structures revealed that <b>5</b> and <b>6</b> are connected by two hexa-<i>peri</i>-hexabenzocoronene (HBC) units and two dipyrromethene or BODIPY units, respectively. As prepared, <b>5</b> and <b>6</b> both show nonaromatic character with figure-of-eight carbaoctaphyrin (1.1.1.0.1.1.1.0) cores and adopt tweezers-like conformations characterized by a partially confined space between the two constituent HBC units. The distance between the HBC centers is >10 Å, while the dihedral angles between the two HBC planes are 30.5 and 35.2° for <b>5</b> and <b>6</b>, respectively. The interactions between <b>5</b> and <b>6</b> and fullerene C₆₀ were studied both in organic media and in the solid state. Proton NMR spectral titrations of <b>5</b> and <b>6</b> with C₆₀ revealed a 1:1 binding mode for both macrocycles. In toluene-<i>d</i>₈, the corresponding binding constants were determined to be 1141 ± 17 and 994 ± 10 M^-1 for <b>5</b> and <b>6</b>, respectively. Single-crystal X-ray diffraction structural analyses confirmed the formation of 1:1 fullerene inclusion complexes in the solid state. The C₆₀ guests in both complexes are found within triangular pockets composed of two HBC units from the tweezers-like receptor most closely associated with the bound fullerene, as well as an HBC unit from an adjacent host. Femtosecond transient absorption measurements revealed subpicosecond ultrafast charge separation between <b>5</b> (and <b>6</b>) and C₆₀ in the complexes. To the best of our knowledge, the present report provides the first example wherein a nanographene building block is incorporated into the core of a porphyrinic framework.