An Extremely-High-Strain All-BODIPY-Based Nanohoop

Highly strained π-conjugated nanohoops present significant synthetic challenges but offer interesting platforms for exploring unique physical properties. Here, we report the synthesis of β-β directly connected strained cyclic Boron-dipyrromethene (BODIPY) tetramer [4]CBDP, with its structure unambiguously confirmed by single-crystal X-ray diffraction. Importantly, the radially conjugated architecture narrows the HOMO-LUMO gap, yielding panchromatic absorption spanning the visible spectrum with an edge extending into the NIR-I window, and results in a large Stokes shift (77 nm). Computational results indicate that [4]CBDP exhibits an extremely-high-strain energy of 155 kcal/mol, which is the highest among various reported nanohoops; yet it remains stable under ambient conditions (air/light) in both solution and the solid state.