Nanographene-Fused Expanded Carbaporphyrin Tweezers

Abstract

A nanographene-fused expanded carbaporphyrin (5) and its BF2 complex (6) were synthesized. Single-crystal X-ray structures revealed that 5 and 6 are connected by two hexa-peri-hexabenzocoronene (HBC) units and two dipyrromethene or BODIPY units, respectively. As prepared, 5 and 6 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 & Aring;, while the dihedral angles between the two HBC planes are 30.5 and 35.2 degrees for 5 and 6, respectively. The interactions between 5 and 6 and fullerene C-60 were studied both in organic media and in the solid state. Proton NMR spectral titrations of 5 and 6 with C-60 revealed a 1:1 binding mode for both macrocycles. In toluene-d(8), the corresponding binding constants were determined to be 1141 +/- 17 and 994 +/- 10 M-1 for 5 and 6, respectively. Single-crystal X-ray diffraction structural analyses confirmed the formation of 1:1 fullerene inclusion complexes in the solid state. The C-60 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 5 (and 6) and C-60 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.