[3]CycloBODIPY: A Highly Strained Cyclic BODIPY Trimer with Effective Macrocyclic Conjugation.

Cyclic oligomers containing porphyrinic chromophores have attracted significant attention in broad areas of science as artificial models for photosynthetic light-harvesting antennae due to their structural and functional resemblance to natural chlorophyll arrays. Here, the synthesis of a macrocyclic [3]cycloBODIPY derivative, which consists of only boron-dipyrromethene (BODIPY) units, via an Au-mediated macrocyclization protocol is reported. While this [3]cycloBODIPY derivative exhibits a high total strain energy of 86.4 kcal mol-1, part of the intrinsic strain is effectively dispersed due to the flexible boron centers. Furthermore, this [3]cycloBODIPY derivative exhibits near-infrared (NIR) absorption reaching 1050 nm as the result of two electronic modulation factors, i.e., deformation of the BODIPY subunits and effective π-conjugation over the entire macrocycle.