Synthesis of π-expanded O-chelated boron–dipyrromethene as an NIR dye

A π-expanded BODIPY dye with an intramolecular boronate skeleton was synthesized by retro Diels–Alder reaction of the bicyclo[2.2.2]octadiene (BCOD)-fused BODIPY and the subsequent O-chelation. The photophysical and electrochemical properties were examined by UV–vis, fluorescence, CV measurements, and DFT calculation. This BODIPY exhibited the absorption and emission over a visible–NIR region at 600–850 nm. O-chelated BODIPY showed a bathocromic shift compared to F-BODIPYs. This dye showed a bright fluorescence emission at 733 nm with the high Φ value of 0.58.