N,O‑Chelated Organoboron Complexes with Seven-Membered Rings

Organoboron complexes have gained considerable attention owing to their versatile chemical structures and excellent optical properties. Nevertheless, stable seven-membered organoboron complexes have rarely been reported because of their challenging synthesis. Herein, seven-membered N,O-boron-chelated dyes, whose photophysical properties have been thoroughly studied via spectroscopic tests and theoretical calculations, were synthesized from commercially available materials via a facile method. Single-crystal X-ray diffraction studies provided evidence of their seven-membered ring N,O-boron-chelated skeleton. These complexes produced singlet oxygen species under laser irradiation, endowing them with potential application as a photosensitizer to treat superficial tumors (B16 cells). Our study provided a new skeleton to construct versatile organoboron compounds and offered a strategy to design heavy-atom-free photosensitizers.